Human Uniqueness: a General Theory Author(S): Paul M

Human Uniqueness: A General Theory Author(s): Paul M. Bingham Source: The Quarterly Review of Biology, Vol. 74, No. 2 (Jun., 1999), pp. 133-169 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/2665093 Accessed: 25/11/2009 12:57

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http://www.jstor.org VOLUME 74, No. 2 JUNE 1999 THE QUARTERLYREVIEW of B JOLOGY

HUMAN UNIQUENESS: A GENERAL THEORY

PAUL M. BINGHAM Departmentof Biochemistryand CellBiology, State Universityof New York StonyBrook, New York11 794 USA E-MAIL: [email protected]

ABSTRACT The extensive, persistent ecological dominance of humans is unprecedented. We display a highly derived social adaptation involving uniquely extensive cooperationamong nonclosekin. Further, humans possess adaptive capabilities, including language, high cognitivefunction, and technological virtuosity not previously seen on this planet. Moreover,this suite of propertiesemerged and was refinedvery rapidly on a geological time scale. Thesediversefeatures of humans presentwhat is referredto as the "humanuniqueness problem. "A theoreticalinterpretation ofthesephenomena is one of the largestremaining challengesto the scientific enterprise.While many interpretationshave beenproposed- several containing important individual insights-none has yet proven robustor complete. A straightforwardresolution of the human uniqueness problemis proposed.It is argued that coalitional enforcement is necessaryand sufficient to allow extensivenonkin cooperation,leading to all majorelements of human uniqueness. Coalitional enforcementarose uniquely in humans when the animals thatfounded the Homo clade acquiredthe ability to kill or injure conspecificsfrom a substantial distance. This resultedfrom the evolution of hominid virtuosity at accurate, high-momentumthrowing and clubbing, previously supposed to be adaptations for hunting, predator defense or individual aggression. No previous animal could reliablykill or injure conspecificsremotely. This ability dramaticallyreduced the individual cost ofpunishing noncooperativebehavior by allowing thesecosts to be distributed among multiple cooperators.The capacityfor coalitional enforcementdrove the evolution of a cooperativesocial adaptation stably and autocatalyticallyfrom the origin of incipient Homo about 2 million years ago through to the present moment-including socially supported,ultimately spectacular, refinementsin weaponryand social monitoring, with attendant increases in efficiencyof coalitional enforcementand thus in the extent of human cooperation.Its details renderedthis evolutionaryprocess very rapid. This theoryis believedto be robust and relatively complete.For example, coalitional enforcementis necessaryand sufficient to allow for the evolution of language in an ape. Further, given the likelyfunctional organization of the ancestral vertebratemind, the coalitional enforcementhypothesis predicts, in addition to genetic information, the emergence of a second streamof design informationin Homo, susceptibleto Darwinian selection.A novel source of design information has long beensuspected on empiricaland intuitive grounds to be responsiblefor the uniquely high level of human adaptive sophistication. The unprecedentedcognitive power of human minds is also predictedby theseimplica- tions of the theory.Lastly, the "cognitiveexplosion" associated with the relatively recent appearance of behaviorally modernhumans is predictedby the theory,as is the increasing size of human political units. The coalitional enforcementhypothesis and its immediateimplications now enable theformerly elusive unification of diversefields of study, including human biology,psychology, linguistics, paleontology, archaeology,anthropology, history,and economics.

133 134 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

[Excerpts from DianaJean Schemo's story "Lynch-MobJustice Grows in Caracas" in the May 13, 1996 issue of the Nezv YorkTimes. It describes a killing in El Encanto, a poor suburb of Caracas, Venezuela, in which the formal state police presence is minimal.] ... when threestrangers attacked some residents on their way to work,stripping themof money,tools and even clothes, the responsewas swift and deadly. "Idon 't know if we all thoughitthe same thing. .. "said Giovanni, 29, afather of two. He zvasamong thefive residentsforced to the ground by the attackers,who slashed their arms and backswith scissors [and] batteredthem zvith a rifle . . . Eventually, Giovanni yanked the rifie away and, finding that it was not real, screamedforhelp. Neighborscame running. Two of the muggersescaped, but a third,Jose HortensioFigueira Reyes,31, was maroonedat the centerof a growing mob of local residents,who rained blows, kicks and stones on him until he was dead. "Wedidn't decideto kill him, "said a 36-year-oldcarpenter named Ruffino . . . It was somethingthat just happened. But afterwardeverybody said, 'At least this way they won't mess with us again '. "Fortwo months they [the muggers] wereholding upfour orfive people a day, said Ruffino the carpenter. Said Giovanni, the victim whofought back, "This was like the sixth time that they had ambushedpeople going to work.People got tired of it. "... Thepolice investigating the [killing] in El Encanto received. . . a statement.with150 signaturesclaiming responsibility. "Idon't feel therecan be any judgment, "Ruffino said, "becauseit was the entire community,not one person. When theyscreamed for help I ran, and many othersdid too. First therewere 50 people, and then morethan 200. "Everyoneagreed that it was well we did it," [Giovanni] said. "Thefeeling of people zvas, 'Lets unite '

M ATURE CONTEMPORARYHUMANS combinations that produce cooperation pref- are highly adept at deceptive manipula- erentially among entities likely to share such tion, and these behaviors exert significant ef- alleles by recent common descent can have a fects on various aspects of human social orga- substantial selective advantage (Hamilton 1964; nization. However, such deception can persist Maynard Smith 1964). These are referred to only as a contingent, minority strategy in the as inclusive fitness effects, and such behaviors context of a larger cooperative social adapta- are said to be kin- selected. Humans show nu- tion. As incomplete and ambivalent as human merous, apparently kin-selected cooperative cooperation commonly is, it is nonetheless far behaviors (see, for example, Daly and Wilson more extensive than among any other large ani- 1988). Moreover, relatedness-based family units mals. It is the ultimate source of human ecologi- have presumably been a characteristic of hom- cal dominance. I focus here on this characteris- inids throughout their evolutionary history. tic and fundamental cooperation in humans. These behaviors are not unique to humans, In spite of their ecological power and capac- however, and they will be of only secondary ity to enhance the fitness of cooperating ani- concern here. mals, highly cooperative social adaptations are Cooperation between animals that are not nonetheless rare, creating the superficial ap- closely related presents a more complex prob- pearance of a paradox. Ground-breaking ear- lem. I will argue below that all major elements lier investigation has substantially clarified the of human uniqueness follow directly from our background to this putative contradiction (Hal- unprecedented levels of nonkin cooperation. dane 1932; Hamilton 1964; Maynard Smith Thus, solving the human uniqueness problem 1964; Williams 1966; Trivers 1971; Dawkins is equivalent to solving the problem of cooper- 1976; Wilson 1978; Symons 1979; Axelrod 1984; ation between nonclose kin. Betzig 1986; Alexander 1987; Daly and Wilson Cooperation between two unrelated ani- 1988; Barkow et al. 1992). Below, I briefly re- mals can produce significant mutual benefit. view the context to the present work that these Commonly such cooperation involves invest- seminal studies provide. ment, in the sense that the cooperating parties Many cases of animal cooperation involve must pay some individual costin return for the closely related individuals. These are inter- individual benefitthat arises from a cooperative pretable as a straightforward extension of the act. When the benefits exceed these costs, co- same simple evolutionary logic that lies be- operation is potentially adaptive. But when such hind cooperation among the cells of a multi- cooperative adaptations arise, they frequently cellular organism; that is, alleles and allelic create a new niche that is even more favorable JUNE 1999 HUMAN UNIQUENESS 135 to individuals than cooperation; it is occupied Although the capacity for remote killing, by those who gain the benefits of cooperation injury is necessary for fully developed coali- while evading its attendant costs. This niche tional enforcement, it is not sufficient. Also has long been recognized from diverse theo- required are cognitive and behavioral devices retical points of view, and its occupants are that control and permit cooperative punish- variously referred to as "social parasites," "free ment in response to parasitic behavior. I will riders," "defectors," or "cheaters," depending refer to these collectively as social monitoring on local intellectual context. devices. I will argue that the acquisition of the As a result of individuals who occupy the capacity for remote killing/injury in early Homo social parasite niche, the cost/benefit ratio for produced-immediately and in a straightfor- cooperators is increased and the adaptive ad- ward way-very strong selection for improved vantage of cooperation is reduced, frequently social monitoring, and thus effective coalitional to the point where the cooperative behavior is enforcement. individually maladaptive. As predicted by these The emergence of coalitional enforcement considerations, nonhuman animals show exis expected to have initiated an autocatalytic tremely limited cooperation between nonclose process in which nonkin cooperation (in addi- kin (reviewed in Taylor and McGuire 1988; tion to its many other adaptive consequences) Dugatkin 1997). supported continuous improvements in wea- Mathematical modeling studies suggest a pon performance and social monitoring. This, formal solution to the social parasite problem in turn, improved the efficiency of coalitional (Maynard Smith 1983; Axelrod 1988; Boyd enforcement, leading to successive and con- and Richerson 1992; Clutton-Brock and Par- tinuous increases in cooperation. It is my hy- ker 1995; Gachter and Fehr 1997, and refer- pothesis that this has been the central process ences therein). Specifically, if a cooperating in the evolution of Homo, beginning some 2 individual can impose a net cost (punishment) million years ago and continuing through to on a parasite that exceeds the net benefits of the present moment. parasitism, then the parasitic strategy ceases The capacity for coalitional enforcement to be adaptive and cooperation can evolve. creates a unique situation in which cooperation However, the fundamental difficulty with such among nonrelatives can consistently promote models is that punishment itself can be costly the inclusive fitness interests of individual ani- to the punishing cooperator (see Maynard mals. Note that many behaviors shaped by this Smith 1982). When the costs of imposing pun- process will be superficially similar to those ex- ishment exceed the benefits of avoiding social pected on theoretically uncertain group-selec- parasitism, punishment and attendant coop- tion models (critiqued in Williams 1966). This eration cannot evolve. misleading fit between the predictions of group- I argue below that this "cost-of-punishment selection models and behaviors produced by problem" has represented the insurmount- enforcement administered by coalitions of self- able barrier to highly cooperative adaptations interested individuals may explain the persis- in all large animals before the origin of Homo. tent intuitive attractiveness of group- selection I further the argue that antecedents of the models for human evolution {also see section Homo solved the lineage cost-of-punishment 3C; section cross-references will be enclosed problem-initially inadvertently-for the first in curved brackets throughout}. time in history by developing the ability to kill or injure conspecifics at a distance by using projectile and clubbing weapons. The ability INTRODUCTION for remote killing/injury permitted a collec- In this article, sections 1 to 4 contain a pri- tion of self-interested individuals to effectively marily analytical development of the coali- and simultaneously attack another conspe- tional enforcement hypothesis and its most di- cific individual. This capability, in turn, sup- rect implications, followed by Sections 5 to 8, ported the emergence of cooperative punish- which review a sample of the extensive empiri- ment-at a greatly reduced individual cost-in cal evidence that supports the theory. Before the context of what I will refer to as coalitional proceeding, it is important to be aware of sev- enforcement. eral points. 136 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

First, the scope and potential generality of 1. DERIVATION OF THE THEORY the theory are large. An adequate sampling of IA. COOPERATION AND COST OF PUNISHMENT the supporting empirical evidence requires a There are several largely independent ways wide range across many traditional disciplin- in which the theory of coalitional enforce- ary boundaries, which obviously carries the in- ment can be derived. One relatively direct der- escapable risk of controversies-many trivial, ivation follows. For simplicity this discussion is but a few that are potentially substantive. More- restricted to a specific subset of cooperative over, because of the massive materials that behaviors involving pairs of conspecific but bear upon the theory, it has frequently been unrelated individuals. necessary to reference the secondary (review) First, in some cooperative behaviors, only literature rather than the primary literature. cooperators can receive the benefits of the be- These references have been carefully chosen havior. I will refer to these as primary mutualis- to provide interested readers with convenient tic behaviors. Mating in many animals is based points of entry to the corresponding primary on primary mutualism. literatures. More commonly, however, it is not only pos- Second, in order to cover the broad scope sible for two animals to cooperate and gener- in this of the theory a short format, paper must ate a mutual benefit, but also for an animal be relatively terse and dense; high attention to pursue an alternative, parasitic strategy in to detail is required to fully appreciate its mes- which some or all of the benefits of coopera- sage. tion are obtained without paying some or all Third, the theory proposed provides a sub- of the cost (investment) necessary to produce stantially new perspective on the available the benefit. Under these conditions, it can be evidence. Under these circumstances, some in the interest of a cooperating individual to elements of evidence and local, empirical gen- inflict an additional cost (punishment) on a erality that were previously thought to be of parasitic individual in order to forestall para- marginal significance (or even irrelevant) be- sitic behavior. Reciprocally, it can be in the come centrally important, and vice versa. Fur- interest of the parasitic individual to inflict ad- ther, this new perspective sometimes suggests ditional cost (extortion) on the cooperating in- different interpretations of individual elements dividual in order to forestall punishment or of evidence than are currently popular. For withholding of cooperation. For simplicity, specialists in some of the relevant areas-such the costs of punishment to each party are as- as history, paleontology, archaeology and an- sumed to be generally similar. Thus, for exam- thropology-such alternative interpretations ple, the cost to the cooperatorof administering may sometimes be initiallyjarring. This initial an individual act of punishment will generally reaction should not be allowed to obscure the be roughly the same as the cost to the parasite possibility of new insight. It will be necessary of experiencing that act. for specialists who wish to confront this work In the second class of cooperative behav- seriously to take the time to understand the iors, the net benefitto the cooperator (defined totality of the theory, rather than merely re- as the gross benefitminus the investment cost of acting to the isolated cases of interpretation the cooperative interaction) exceeds the in- of empirical evidence that are at variance with vestment cost itself. Under these circumstances, older, more local perspectives. the cost of punishment that the cooperator is Fourth, though many elements of available willing to incur will exceed the cost of extor- empirical evidence provide compelling support tion the parasite is willing to incur. for the coalitional enforcement hypothesis, A simple quantitative example illustrates this evidence was originally collected within this. Suppose a cooperative behavior requires traditional theoretical frameworks. Such evi- the investment of 2 units of cost by each coop- dence is inevitably less than optimal for a test erator and generates 5 units of benefit to each of new theory. It will therefore require the fu- cooperator, or 5 units of benefit to a parasite ture efforts of many scholars to fully test and and none to the parasitized cooperator (the refine the coalitional enforcement hypothesis suckerin game theory nomenclature). Under for human uniqueness. these conditions, the cooperator will be will- JUNE 1999 HUMAN UNIQUENESS 137 ing to incur additional cost in the form of pun- lB. COST OF PUNISHMENT AND THE ishment up to incrementally less than 3 units, ORIGIN OF Homo leaving a small residual net benefit. In con- Low-return cooperative behaviors can be- trast, the potential parasite will be willing to come mutualistic if the cost/benefit logic of incur no more than incrementally less than 2 cooperation and punishment can be changed. units of cost in extortion. Under these condi- There is apparently only one straightforward tions, parasitism is a less fit strategy than coop- way to do this. Implicit in the treatment above eration, and thus cooperation can potentially is the assumption that the cost of a punish- evolve. I will refer to the resulting cooperative ment event is borne exclusively by a single co- behaviors as seconda?ymutualism. operator. This is likely to be the case for non- In the third class of cooperative behaviors, human animals {1D}. However, if the cost of the net benefit is less than the investment cost. punishment can be distributed among multi- Under these circumstances, the cost of extor- ple cooperators, this cost to individual cooper- tion that the parasite is willing to incur will ators can be reduced. exceed the cost of punishment the potential I will argue in detail below that such an abil- of Homo as a cooperator is willing to incur. ity arose uniquely at the origin result of the development-initially for other Again, a simple quantitative example will il- purposes-of efficient throwing and clubbing lustrate this. Suppose a cooperative behavior {2; 5A}. Early species of Homo could thereby reli- requires the investment of 4 units of cost by ably kill or injure conspecifics at some distance each cooperator to generate 5 units of benefit away.This ability for killing or injuring remotely to each cooperator or 5 units of benefit exclu- in turn allows a coalition of animals to cooper- sively to the parasite. Under these conditions atively punish parasitic behavior at low individ- the cooperator will be willing to invest up to ual cost-a capacity apparently not possessed incrementally less than 1 unit of cost in pun- by any other animal in history. Below and in ishment, but the parasite will be willing to in- the following subsection {lc}, I develop the vest up to incrementally less than 4 units of formal theoretical framework for this solution cost in extortion. Under these conditions the to the cost-of-punishment problem. cooperative behavior cannot evolve. Such be- Before continuing, it is important to recog- haviors are thus, in practice, altruistic. nize the context in which the solution arose. The only cooperative behaviors among non- Judging from the common properties of chimps, kin that can evolve are those that are fre- bonobos and humans, their last common an- quently mutualistic. Behaviors that are consis- cestor most likely lived in relatively small, sta- tently altruistic, of course, cannot evolve. There ble groups in which animals recognized one are two crucial implications in this context. another as distinct individuals {2}. These ances- First, many potentially cooperative behaviors tral groups are thought to be the products of will involve a modest return on a relatively kin-selected behavior and natural selection for large investment-as in the case in the preced- primary and secondary mutualism. The cost/ ing example. I will refer to these as low-return benefit logic of punishment is expected to evolve in such animals on the basis of some cooperative behaviors. These will not evolve assessment of the aggregatefuture costsof para- within groups of nonkin under the above con- sitism at the hand of each potential punish- ditions. ment target. Second, it is likely that many, if not most, In such a social environment, the aggregate cooperative behaviors in a highly developed future cost of parasitic behavior to any individ- social adaptation will be low-return cooperative ual is generally the same, whether punishment behaviors. Thus, for animals constrained to is individually or cooperatively administered. behave as described in the model above, the However, the individual cost of punishment is cost/benefit structure of cooperation must be profoundly affected by whether punishment such that a highly developed social adaptation is individually or cooperatively dispersed. involving groups of nonkin will be inacces- As a simple quantitative example, consider sible. the cooperative behavior described in section 138 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

IA, in which the cost to cooperators was 4 units of parasites and declining frequencies of co- and the benefit to cooperators or to a parasite operators until the fitness of the parasites is was 5 units. When punishment is individually reduced below that of individuals in other administered, the sustainable cost of punish- populations where coalitional enforcement is ment (about 1 unit) is much less than the sus- the dominant strategy. Thus, coalitional ex- tainable cost of extortion (about 4 units), and tortion is expected to evolve only as a contin- the behavior cannot evolve. But if five cooper- gent, minority strategy-as it is, in fact, in con- ators can distribute the cost of punishment temporary humans. among themselves, the cost to cooperative individuals can remain below 1 unit, while the cost Ic. LANCHESTER'S LAW AND to the parasitic individual can exceed 4 units. COALITIONAL ENFORCEMENT Under these changed conditions of cost/ More detailed treatment demonstrates that benefit, formerly altruistic behaviors can arise the adaptive opportunity presented by coali- as mutualistic strategies. I will refer to cooper- tional enforcement is substantially greater ative behaviors of this form as tertiary mutu- than may be immediately apparent from the alism, and to such cooperative punishment as preceding section. I propose that Lanchester's coalitional enforcement. Coalitional enforcement Square Law, which describes attrition during behavior can be individually adaptive and, un- contemporary mechanized warfare (Lanches- der conditions permitting it, should evolve. As ter 1916; reviewed in Lepingwell 1987), is also long as cooperators engaging in coalitional applicable to conflict with simple weaponry enforcement are in a substantial majority, par- such as thrown projectiles and clubs. If so, the asites will be driven to or near extinction. cost/risk to individual cooperative punishers Coalitional enforcement in the example de- decreases as an exponentialfunction of the ef- scribed above is itselfa primarymutualistic behav- fective ratio of punishers to target. ior. That is, under these specific circumstances, This effect arises as follows. First, increasing the benefit of the cooperative behavior (pun- the relative number of punishers decreases ishment) can be had by any of the cooperating the time required to disable or kill the tar- individuals, but only if all cooperating individ- get(s), thereby terminating the conflict. Sec- uals punish. This may represent the rudimen- ond and simultaneously, when the relative tary form of the behavior. Once initially estab- number of punishers is increased, the risk of return or lished, however, coalitional enforcement is defensive fire from the target(s) is perforce distributed among more punishers. expected to expand to punishing not only par- The following simple quantitative examples asites, but also cooperators who refuse to pun- illustrate this. In one-on-one conflict, each party ish {see subsection ic for details}. Under these will generally have about an equal chance of circumstances, it will be a robust and stable being disabled or killed, thus terminating the strategy. conflict. In contrast, with ten effective punish- Note that a converse of coalitional strategy ers and one target, the target will almost cer- extortion,where coalitions extort contributions tainly be killed or disabled (with a nearly 100% from other individuals without correspond- probability) in about one-tenth the time re- ing reciprocity, is also possible. There are fun- quired in a one-on-one conflict. Moreover, the damental differences between coalitional en- risk of return fire from the single target is dis- forcement and coalitional extortion though. tributed among ten punishers. Conflict dura- Coalitional enforcement is self-sustaining. In tion is reduced tenfold anddefensive fire from contrast, local populations in which coalitional the target is distributed among ten punishers, extortion is a common strategy are dynami- producing a net one-hundredfold effect. The cally unstable. Coalitional extortion is highly probability that any individual punisher is fit only when the frequency of cooperators- killed or disabled by return fire from the target i.e. parasitic targets-is high enough to support is thus reduced to less than 1% with a ten-to- parasitism, but low enough to prevent coali- one punisher-to-target ratio. Analogously, with tional enforcement from driving the extortion a 100-to-i punisher to target ratio, the risk of to extinction. Coalitional extortion under these disability or death to any individual punisher conditions will lead to increasing frequencies is less than one in 10,000 per episode. JUNE 1999 HUMAN UNIQUENESS 139

These properties of projectile weapon pun- throughout the some 2-million-year history of ishment have the following crucial, interre- the Homo clade. lated implications. First, there will be strong selection for punishing cooperators to induce 1D. ENFORCEMENT IN NONHUMAN ANIMALS nonpunishing cooperators to punish, thereby To see that the above treatment accurately producing the exponential reduction in indi- reflects the enforcement problem in nonhu- vidual risk. man animals, consider punishment as it actu- Second, as a result of these exponentially ally occurs. Individual acts of punishment take declining risks, there will be only relatively diverse forms, including the denial of future weak selection for cooperators to resist pun- access to a resource (such as food), inflicting ishing. Thus, nonpunishing cooperators will injury or death on a juvenile relative of the be a minor rather than a major impediment target individual, or inflicting injury or death to the emergence of coalitional enforcement directly on the target individual. However, and tertiary mutualism. These two implications, even in cases where the primary sanction is not collectively, indicate that the emergence of the injury or death to the target individual, this capacity for remote killing/injury of conspecif- sanction will generally require a threat of such ics is the key to the solution not only of the injury or death. For example, threats will gen- cost-of-punishment problem itself, but also of erally be required to repulse the target individ- the crucial subsidiary problem of why exten- ual's advances toward a resource. In turn, for sive punishing of nonpunishers arose uniquely threats of injury or death to be credible they in humans. [See Maynard Smith (1983), Axel- must be generally realistic (Dawkins and Krebs rod (1988) and Boyd and Richerson (1992) 1978; Grafen 1990; Zahavi and Zahavi 1997, for general, formal discussions of the back- and references therein). ground to this subsidiary theoretical problem.] Thus, all capacity to punish is limited by the Third, there will be strong selection for actual capacity of the punishing animal to de- punishing cooperators to improve coordina- liver injury or death to the target animal. This tion of punishment episodes in order to max- constraint is severe for nonhuman animals, imize exponentially reduced individual risk. for the simple reason that their strategies for Improved social monitoring permits this. injuring and killing are proximal; in order to Fourth, as a result of decreased punishment kill or injure a conspecific, any nonhuman ani- costs, the number and consistency of tertiary mal, no matter how individually formidable, mutualistic behaviors will tend to increase as must inevitably engage in a struggle at close an exponential function of social monitoring quarters with an animal of very similar capabil- efficiency and projectile weapon range. ity. Such proximal strategies produce onlyvery In summary, I propose that coalitional en- limited capacities for more than one animal forcement has been an inaccessible adapta- to participate in killing or injuring another tion for all animals before the emergence of conspecific animal. Under these conditions, humans. The capacity to use clubbing and the individual costs of punishment are ines- projectile weapons to kill or injure remotely, capably great, and the credibility of threat is developed in the immediate ancestors of correspondingly limited. Homo, created the first animals in terrestrial history to which efficient coalitional enforce- 2. EMERGENCE OF COALITIONAL ENFORCEMENT ment-and large scale tertiary mutualism- Many details of the origin of coalitional en- was accessible. Moreover, in view of Lanches- forcement in incipient Homo will likely never ter's Square Law, once coalitional enforcement be known. A number of constraints on and supported by projectile weaponry and the re- features of this emergence can be reasonably sulting expanded cooperation emerge, they inferred, however. First, the hominid popula- are expected to be very rapidly refined and tion immediately ancestral to incipient Homo expanded. Further, ongoing selection for im- had morphological properties consistent with provements in weaponry is expected, with cor- the requirements of the coalitional enforce- responding increases in efficiency of coali- ment hypothesis. Specifically, this ancestral tional enforcement and, thus, cooperation australopithecine lineage was no doubt signif- 140 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74 icantly more bipedal than the last common 3. ALTERNATIVES TO THE THEORY ancestors of chimps and humans. Under these 3A. INDIVIDUAL AGGRESSION, AMBUSH circumstances, redesign of the skeleton to sup- AND REVENGE port improved throwing and clubbing was sus- The capacity for remote injury or killing tainable {see 5A}. uniquely confers on humans not only the ca- Second, under these circumstances, simple pacity for coalitional violence but also for suc- selection for improved ability to knock down cessful blind ambush. This capacity is unlikely inaccessible fruit or to defend against preda- to be responsible for any significant larger hu- tors, for example, is expected to have led to man novelty, however. The reason is that indi- improved projectile and clubbing weapon ca- vidual ambushers are highly vulnerable to re- pability. By hypothesis, this capability improved ciprocal ambush (revenge) at the hands of the to the point that it allowed injury or death to target, or close kin of the target. be reliably inflicted on a conspecific from a This is a specific case of the general point significant distance, in at least the one local that the use of projectile and clubbing weap- australopithecine population ancestral to Homo. ons in one-on-one combat is expected to be Third, available evidence indicates that subject to the same selective constraints as in- chimps are capable of strategic cooperative vi- dividual aggression mediated by tooth and olence against conspecifics to the very limited claw. Such behaviors are risky and costly, and animals are expected to use them in those extent sustained by their largely proximal kill- only relatively rare cases when the adaptive benefits ing strategies (reviewed in de Waal 1982, 1989; outweigh the formidable costs. Harcourt and de Waal 1992). Thus, this capac- Beyond this, coalitional enforcement itself itywas likely present in the last common ances- is expected to curtail weapon use for one-on- tors of chimps and humans, and therefore in one aggression, compared to such behaviors the australopithicine population immediately in nonhuman animals. Specifically, coalitional ancestral to Homo. Under these circumstances, killing of unusually aggressive individuals can rudimentary coalitional enforcement is expected be adaptive to individual coalition members to have emerged in incipient Homo as merely {5B}. Thus, using weapons for one-on-one ag- an expansion of this pre-existing capability gression will frequently backfire in the context permitted by improved clubbing and throwing. of a small, stable coalition whose members can Fourth, much of nonhuman ape coopera- kill remotely and cooperatively. Therefore, tion, including cooperative violence, is likely somewhat paradoxically, the availability of re- to represent kin-selected behavior (reviewed liable remote killing capabilities should reduce in Harcourt and de Waal 1992; Wrangham rather than increase individual aggressive be- and Peterson 1996). Thus, rudimentary coali- havior. Consistent with this view, contempo- tional enforcement in incipient Homo likely rary humans are unique among top predators had the initial effect of merely extending such in being relatively placid in their dealings with cooperative behaviors to progressively lower unrelated conspecific nonmates under a wide variety of circumstances. levels of kinship. Under these conditions of Lastly, while the capacity for revenge con- emergence, coalitional enforcement is expected strains the importance of one-on-one ambush, and coalitional extortion {1B} would have re- it has no such effect on coalitional enforce- mained a marginal, contingent strategy. ment. Specifically, subsequent attempts at re- Fifth, collectively these circumstances are venge by a target of coalitional enforcement expected to have supported the emergence can be as cost- effectively punished coopera- and rapid refinement of coalitional enforce- tively as any other parasitic act. ment and tertiary mutualism {1B, Ic}. On the coalitional enforcement hypothesis, this emer- 3B. THE HUNTING HYPOTHESIS gence was the decisive event in the divergence It has been suggested by others that early of the australopithecine and Homo lineages evolution of human cooperation was driven by and, based on current evidence, likely oc- the adaptive advantages of meat sharing (re- curred 2.0 to 2.5 million years ago. viewed in Tooby and DeVore 1987). On this JUNE 1999 HUMAN UNIQUENESS 141 view, human weapon use arose primarily as enging reflects a sustainable constellation of part of a hunting or scavenging adaptation. tertiary mutualistic behaviors. That is, coali- While hunting/scavenging appears to have tional enforcement solves the cost-of-punish- had at least some adaptive importance to early ment problem, so that both participation in hominids, this hypothesis is flawed as a funda- still occasionally risky hunts, and the system- mental theory of human uniqueness. atic distribution of kills, are sustainable adap- First, meat sharing among nonkin is a spe- tations. cific case of cooperation for which the cost-of- It remains a problem for future investiga- punishment problem must be solved before it tion to establish in detail the importance of can be a sustainable adaptation {1A}. Hunting hunting/scavenging to early Homo. Though hypotheses to date either ignore this problem, the current view that hunting/scavenging or simply stipulate that it has been solved in were adaptively significant behaviors seems some unspecified way. plausible, the coalitional enforcement hy- Second, earlier hypotheses on hunting fail pothesis does not require it. Indeed, it would to explain why the other social carnivores of have been formally possible for the use of the African savanna did not also develop elab- weapons to sustain the long evolution of the orately cooperative social adaptations. [Note human social adaptation in the complete ab- that the limited social cooperation, including sence of carnivory. cooperative hunting/scavenging, in nonhu- It is noteworthy that modern hunter/gath- man savanna carnivores appears to reflect kin- erers, living at latitudes similar to those of selected and primary mutualistic behaviors.] early Homo, frequently derive only a small por- With these considerations in mind, it is im- tion of their total food value from hunting/ portant to interpret human hunting/scaveng- scavenging (Kelly 1995). It is also noteworthy ing, especially the highly cooperative hunting that one effect of improved weaponry during of recent modern humans, in the context of recent human evolution has frequently been the coalitional enforcement hypothesis. On a reductionin dependence on hunting {see 6D}. the basis of the discussion in subsection 1c, it is This is an unexpected consequence of any now possible to propose a more sophisticated simple version of the hunting hypothesis, but version of the hunting hypothesis to explain predictable from the coalitional enforcement human uniqueness. Specifically, human unique- hypothesis. ness might be supposed to result ultimately from the capacity of remote weaponry to allow 3c. THE WARFARE HYPOTHESIS individual risk in cooperative hunting/scav- Darwin (1871) originally proposed that inter- enging to be reduced as an exponential func- group warfare was the basis of human unique- tion of the number of hunters, while individ- ness. This hypothesis has been repeatedly re- ual return is potentially reduced as a linear vived and refined since that time. The various function of this number. restatements of this hypothesis can be consid- While this effect is no doubt significant, it ered equivalent to the following: When hu- is important to note that this new version of mans within a group cooperate, they are able the hunting hypothesis still fails, not only as a to compete successfully in warfare with other general theory of human uniqueness, but even human groups that are less cooperative. Thus, as a theory of hunting/scavenging involving it can be inferred that surviving humans are cooperation of nonclose kin. Specifically, it is descended from those who were members of unable to account for the sustainable distribu- such cooperative groups. More general state- tion of the risks and products of cooperative ments of the hypothesis are broader, and in- hunting/scavenging among nonkin, much voke all forms of intergroup competition, in- less the broad, extensive tertiary mutualism of cluding warfare. humans in general {see, for example, 4-7}. But such models are flawed as explanations In contrast, the coalitional enforcement hy- of human uniqueness. First, they are all group pothesis accounts for all of these behaviors, selection models. They posit that human groups including modern hunting. On this hypothe- win competitions based on previously existing sis, highly cooperative human hunting/scav- differences among the cooperative behaviors 142 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74 of their members, and that this selection is suffi- having achieved unprecedented "ecological ciently strong to sustain cooperative behaviors dominance," such that the primary "hostile that are nonetheless individually disadvanta- force of nature" for humans was other humans geous within the group. [Recall that parasitic (Alexander 1990). This is proposed to lead to strategies commonly have higher individual runaway group selection. Alexander's contri- fitness in the absence of coalitional enforce- butions in this area are many and formidably ment {1A; 1BI.] While such models are not in- important; however, this particular suggestion herently inconceivable, an extensive body of is unlikely to be correct as a primary theory of evidence since Williams's (1966) seminal work human uniqueness for the following reasons. indicates that the circumstances under which On the one hand, this suggestion is argua- they will apply are very limited. bly credible for very recent modern humans, More specifically, in order for such models but notably not for most of the history of the to be credible, the following crucial question Homo clade. Specifically, there is no evidence must be answered: Can selection at a simpler that Homo habilis or Homo erectus/ergasterwas organizational level produce the same effect? more ecologically dominant than any other Or, equivalently, is there a more direct selec- member of the diverse savanna carnivore guild tive route to the same outcome? If the answer or, for that matter, various large herbivores to this question is yes, group selection effects like elephants. are very likely to be either secondary or irrele- On the other hand, this formulation is im- vant. A central point of the hypothesis pre- plicitly circular: on this view, humans are eco- sented here is that coalitional enforcement logically dominant because they cooperate, apparently provides precisely such a more di- but the proposed selection for cooperation re- rect route to human cooperation. Thus, group quires prior unique ecological dominance. selection effects, including those invoked in The empirical record is also illuminating the warfare hypothesis, are most unlikely to be here. Intergroup warfare is expected to leave of primary importance. one unique paleontological artifact-sites in- This can be visualized intuitively as follows: volving multiple individuals killed simultane- Under group selection models, human coop- ously with human weapons. While such sites erative behaviors must arise within groups, are found in the very recent record (the last even though they are often individually mal- 10,000-40,000 years or so), they are unknown adaptive in that context. These groups must throughout the 2-million-year history of the then come into sufficiently intense competi- Homo lineage before this time (Keeley 1996). tion with other groups so that these intragroup This chronology is exactly what would be ex- disadvantages are offset by the rewards of win- pected on the coalitional enforcement hy- ning such competitions. Moreover, such in- pothesis {see 6 for details}, but not on the war- tergroup competition must recur sufficiently fare hypothesis for human uniqueness. often to offset the persistent subversion of co- Finally, once coalitional enforcement arises, operation as a result of its intragroup individ- a subset of resulting cooperative behaviors- ual disadvantages. those supporting intergroup competition- In contrast, on the coalitional enforcement yield secondary group selection effects that hypothesis intragroup(intracoalition) coopera- reenforce the primary effects of coalitional en- tion emerges automatically and is stably main- forcement. These secondary effects are appar- tained by the individual, self-interested en- ently entirely dependent on the previous exis- forcement actions of coalition members. The tence of coalitional enforcement, however. fitness of individual coalition members is thus There is no reason whatsoever to suppose that enhanced as a consequence of diverse cooper- such group effects alone are sufficient as pri- ative behaviors-including, among many oth- mary selection for human social behavior. ers, the capacity to wage effective warfare when the occasion arises. 3D. OTHER HYPOTHESES Further, the most sophisticated recent for- Models for human uniqueness have been mulations of the warfare hypothesis suggest proposed that are sometimes referred to as that their uniqueness results from humans "combinatorial hypotheses." These models as- JUNE 1999 HUMAN UNIQUENESS 143 sume that humans possess a unique combination to "cultural" evolution have been pursued in of adaptations that are shared individually with every generation since Darwin (Richards 1987; various other animals. For example, human Degler 1991). Exploration of such approaches uniqueness might result from some combina- by biologically oriented investigators has con- tion of social ancestry, bipedality (permitting tinued through the present (see, for example, provisioning and transport) and carnivory on Dawkins 1976; Alexander 1979; Cavalli-Sforza such a view. The number and diversity of such and Feldman 1981; Lumsden and Wilson 1981; models is enormous, and I will not attempt to Boyd and Richerson 1985; Williams 1988; Dur- critique them individually here. ham 1991; Boyer 1994; Dennett 1995; Sperber There are two general problems, however. 1996, and references therein). Further, sev- First, in spite of their diversity, no individual eral strong "evolutionist" traditions have long combinatorial hypothesis has garnered wide existed within anthropology and archaeology empirical support, and most are equally plau- (Arens 1986;Johnson and Earle 1987; Tainter sible (or implausible). Second, most are highly 1988; Pauketat 1994; Marcus and Flannery local in application. For example, some ac- 1996; Maschner 1996), and are found in psy- count with at least superficial plausibility for chology and economics as well (Simon 1981). the origin of Homo but not for the rise of, say, This enormous body of ground-breaking Bronze Age Kingdoms or vice versa. work has made it increasingly clear that Dar- In contrast, the hypothesis developed here winian processes are somehow involved in hu- is unitary. I will argue that all the major non- stochastic evolutionary events of the Homo lin- man evolution, not only in the genetic domain eage, from its origin through the present mo- but also in an additional "cultural" domain. ment, have a single primary cause-the rise Most of the details of this process have re- and ongoing refinement of coalitional en- mained obscure and contentious, however. For forcement with its diverse supporting "tech- example, the precise way in which such a do- nologies" and adaptive consequences. main might have arisen and might function has remained unclear. Moreover, the reasons 4. LANGUAGEAND why such a novel informational domain might EXTRAGENETICINFORMATION be unique to humans, at least quantitatively, has remained unknown. As a result, in spite 4A. CONTEXT of the importance of this general insight, its In addition to its theoretical coherence, the applications to date have been muddled, and coalitional enforcement hypothesis for human it has had an astonishingly limited impact on uniqueness is attractive on empirical grounds. the understanding of human behavior and Elements of this observational support are re- evolution. viewed in sections 5 to 8 below. Many of these Much of the confusion in this area, in turn, phenomena in turn are dependent on a very results ultimately from the fact that insight has basic implication of the coalitional enforce- been almost or observational ment hypothesis. Specifically, the hypothesis entirely empirical provides a straightforward explanation of the in origin. A credible theoreticalframework that origin of human communication-including accounts for and predicts these phenomena language-and the associated emergence of a has not been available, and no earlier treat- novel stream of design information support- ment is based on a plausible theory of human ing the unique sophistication of diverse hu- cooperation {1} or of the origin of human lan- man adaptations. This implication of the the- guage {4c}. ory is reviewed here. The coalitional enforcement hypothesis provides this previously missing theoretical 4B. HISTORY OF ANALYSIS OF LANGUAGE framework. Its implications, in turn, allowvari- AND CULTURE ous formerly isolated elements of insight from The recognition that humans have, in some the large body of earlier seminal work to be sense, a "cultural heritage" acquired from unified in a coherent, straightforward theory other humans and contributing to adaptation of human evolution controlled by two partially is ancient. Moreover, Darwinian approaches independent streams of design information. 144 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

4c. LANGUAGE Jackendoff 1994, Pinker 1994 and Deacon 1997 It has been clear since Darwin that human for reviews of the currently recognized funda- linguistic competence has the complex, co- mental properties of human language.] In herent structure expected of a highly derived particular, extensive genetic adaptation to lan- adaptation to functions that include support guage production and perception is expected of information exchange. Further, it has been and observed. Moreover, given limitations on obvious that such exchange implies a long his- amounts of available genetic information, ex- tory of unusually cooperative social adapta- tensive combinatorial cooperation among ele- tion. In spite of this, there has been isolated ments of "learned" information, and between resistance to adaptationist interpretations of genetic and "learned" information in the cre- human language through to the present. This ation of contemporary language, is expected resistance has been possible, in part, because and observed. {See 4E-F for a discussion of this of the absence of a credible theory that ex- "learning" and cooperation in the context of plains the context and logic of language evolu- the coalitional enforcement hypothesis.} tion. The coalitional enforcement hypothesis Note that the coalitional enforcement hy- appears to provide this. pothesis predicts the emergence of expanded Animals are expected to engage in system- information exchange, using all applicable atic hostile manipulation of one another in sensory modalities and combinations thereof. pursuit of relative (genetic) inclusive fitness Thus, the hypothesis predicts emergence not advantage. As a result, honest signals are ex- only of language, but also of expanded "non- pected only under limited circumstances. In linguistic" communication (such as gestural nonhuman animals these can include threat communication) in the Homo clade. Also note and kin-based cooperation. Put anthropomor- that the episodic, contingent use of language phically, because nonhuman animals are free for "dishonest" purposes in contemporary hu- to lie to one another, the information provided mans is secondary. This parasitic use of language by one animal to an unrelated conspecific is is dependent on the fundamental presump- commonly unreliable, and there is no selection of honesty in communication, and is fre- tion for adaptation to generalized exchange quently punished by other coalition members. of such information. As predicted by these theoretical considerations, most animals are ob- 4D. HUMAN ADAPTATION AND served to show only highly limited honest sig- EXTRAGENETIC INFORMATION naling among nonkin (Dawkins and Krebs The specific element of human uniqueness 1978; Grafen 1990; Zahavi and Zahavi 1997, most directly responsible for ecological domi- and references therein). nance is intellectual/technological virtuosity- In contrast to nonhuman animals, under ap- some recent claims to the contrary notwith- propriate circumstances contemporary humans standing (critiqued in Gross and Levitt 1994). exchange extravagant amounts of relatively The human capacity to understand and ma- reliable information with unrelated conspecif- nipulate the world is far greater than that of ics. The coalitional enforcement hypothesis any other animal. This capacity is so extensive predicts this uniquely human behavior as fol- that it can be viewed as a qualitatively new ad- lows: coalitional enforcement allows low-cost, aptation. In the words of a thoughtful discus- cooperative punishment {1B, lc} of dishonest sion of this issue, humans are the first animal communication within coalitions. This has the to occupy the "cognitive niche" (Tooby and effect of substantially reducing the net benefit DeVore 1987). The question has remained as of many acts of hostile manipulation, while to why this is uniquely true of humans. I argue leaving undisturbed the adaptive opportuni- that human intellectual/technological virtu- ties for mutualistic exchange of reliable infor- osity is a direct consequence of coalitional en- mation in this specific context. forcement. Once the human cooperation problem is It is first necessary to define more precisely solved by the emergence of coalitional en- the problem to be solved. The products of hu- forcement, evolution of language with its vari- man intellectual/technological virtuosity show ous well-known properties will follow. [See a striking analogy to those of genetically con- JUNE 1999 HUMAN UNIQUENESS 145 trolled adaptive design in nonhuman organ- information content of this domain grew very isms. For example, humans use technological much larger relatively abruptly with the emer- products such as aircraft and weaponry, in gence of behaviorally modern humans. part, to solve the same adaptive problems I argue that coalitional enforcement is nec- solved by genetically determined devices of essary and sufficient to support the emergence wing, tooth and claw in nonhuman animals. of a novel informational domain that has all It is widely recognized that Darwinian selec- of these properties. First, the emergence of tion is probably the only possible source of this large scale mutualistic information exchange- adaptive design in human artifacts. Confusion including linguistically supported communi- has arisen in trying to understand in detail how cation-between nonclose kin is allowed by this general insight actually applies, however. coalitional enforcement {4c}. This creates in- The most common mistake is to assume that formation (hereafter referred to as extragenetic conventional Darwinian processes operating information) that is stored in memory and can on genetic information produce human minds be transmitted indefinitely and independently whose properties somehow include generation of small kinship groups. Any elements that of the novel, complex adaptive design re- also produce adaptive design in hominids that transmit extragenetic information will be se- flected in human material artifacts sui generis. lectively favored {see 4E-F for details}. Such explanations pervade not only the so- Second, it has long been recognized that cial sciences but even some subareas of the Darwinian theories of cultural evolution re- neurosciences. They are apparently incoher- quire that the underlying design information ent, however. And conspicuously, they fail to be replicated with sufficient fidelity on the one explain human uniqueness. If building such hand, while undergoing sufficient variation minds by the action of Darwinian selection on on the other, to support Darwinian processes. genetic information were somehow possible, However, it has remained unclear as to how this adaptation would presumably be recur- such capacities might have arisen or how they rent. Instead, it is unique to humans. might currently function. I will argue below Before turning to a possible resolution of that these properties emerge with compelling this confusion, two additional properties of simplicity in the specific context of enforcing human technological innovation must be re- coalitions, given one robust theory of how ani- called. First, its scale has recently become mas- mal minds work {4E-F}. sive with the emergence of behaviorally mod- Third, transmission of and selection op- ern humans about 40,000 years ago. Second, erating on extragenetic information is at least the speed of modern human innovation is un- partially independent of biological reproduc- precedented and sometimes appears to ex- tion of the organism {4E-F}. Thus, novel adap- ceed rates achievable by the action of Darwin- tations produced by Darwinian processes act- ian selection on genetic information. ing on this information can arise on time scales In view of these considerations, the theoret- of less than a single generation. ical challenge presented by human intellectual/ Fourth, as a straightforward consequence technological virtuosity would be well-met if of coalitional enforcement, the amount and the following were true. First, if there emerged quality of available extragenetic information is to an at uniquely and stably in early Homo a new infor- expected undergo abrupt, rapid growth a specific point in the evolutionary history of mational domain, partially or largely indepen- hominids. Thus, the well-documented but for- dent of genetic information. Second, if infor- merly poorly understood "cognitive explosion" mation in this domain is susceptible in some associated with the recent origin of behavior- fashion to Darwinian processes, thus repre- ally modern humans emerges as a direct pre- senting a novel source of adaptive design that diction of the theory. {See section 6 for details.} controls, among other things, the properties of the artifacts of Homo. Third, if transmission 4E. EXTRAGENETIC INFORMATION: and selection of information in this domain FIRST ORDER REFINEMENTS operates such that novel adaptive design can In this and the following two subsections, sometimes be generated on time scales of less selected elements of the theory of extragenetic than a single human generation. Fourth, if the information outlined immediately above are 146 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74 developed in more detail. This discussion is netic devices that, in turn, impose indirect designed to make the economy and high plausi- selection on extragenetic information could bility of the theory more clear and to increase well be sustainable. Under such conditions the accessibility of later sections. [For simplic- the extragenetic domain can apparently be- ity, the phrase "by hypothesis" will be omitted come quite large 16, 81. throughout the lists in subsections 4E-F.] The postulate of indirect selection on extra- First, extragenetic information consists ex- genetic information emerges not only directly clusively of information encoded in long-lived from the coalitional enforcement hypothe- neural structures capable of influencing be- sis, but also indirectly and independently from havior, however indirectly, and capable of a powerful class of theories of how minds transmission to other hominids, often but not work-as will be discussed immediately below. always with linguistic support. This insight is of the most fundamental impor- Second, I argue that we are now in a posi- tance, and few of the arguments throughout tion to clarify significantly the vexing problem the remainder of the paper can be fully ap- of how and why replication-with- variation and preciated without a firm grasp of its signifi- selection in the domain of "cultural" (extrage- cance. netic) design information originated and op- This insight indicates that our confidence erates. It is useful to begin with the following in the postulate of indirect selection should two definitions. be very high. Moreover, it provides the first On the one hand, analogously to the ge- coherent, robust explanation for the evolu- netic domain, there is direct selection on ele- tionary origin of replication, variation and se- ments of extragenetic information as a result lection within the extragenetic domain. This of their phenotypic effects on the viability and insight leads directly to a clear formal explana- fecundity of individual hominids holding and tion of the unique cognitive power of human potentially transmitting this information. On minds. the other hand, extragenetic information is The powerful class of theories of mind men- stored mentally, so elements of such informa- tioned above proposes that mental functions, tion can interact with one another. Thus, direct including at least some of those subjectively selection can create both genetic and extrage- experienced as perception and cognition, re- netic devices that operate on other elements sult from the operation of managed, internal of extragenetic information, and thereby im- Darwinian systems (see, for example, Jerne pose indirectselection affecting the survival and 1967; Edelman 1987; Changeux and Deheane transmissibility of this information. [I will use 1989; also see Plotkin 1993 for a recent re- "genetic" and "extragenetic" devices hence- view). In simplified overview, such systems forth as shorthand for informational, behav- function by generating multiple alternative in- ioral, morphological or material devices whose formation structures and by competitively design is controlled or substantially influenced choosing among them on the basis of fit, con- by genetic or extragenetic information, re- gruence or interaction with other information spectively.] Note that such selection is "indi- structures-all within an individual animal. rect" only from the perspective of the homi- In the case of perception, for example, nids who transmit the information. From a members of sets of internal information struc- perspective internal to the extragenetic infor- tures representing possible organizations of mational domain, this selection is direct. salient features of the external environment Indirect selection in the extragenetic do- are competitively tested for quality of congru- main is a compelling theoretical requirement. ence with incoming sensoly data. Partially di- Specifically, selective loads are apparently near vergent copies of the "best fit" from one round maximum in animal populations, and large are then regenerated and retested competi- numbers of additional deaths or reductions in tively in a second round, and so on. A rapid fertility as a result of selection on extragenetic (unconscious) series of such rounds ulti- information are not expected to be sustain- mately produces what we experience subjec- able. However, relatively small numbers of ad- tively as "recognizing" our immediate physical ditional deaths shaping genetic and extrage- environment. Thus, "recognition" here ulti- JUNE 1999 HUMAN UNIQUENESS 147

mately results from selection on members of Because individual vertebrate minds are in- arrays of competing percepts based on other herently Darwinian processing devices, these mental information-in this case, sensory in- newly emergent, multigenerationally persis- formation. tent serial arrays in Homo inevitably process in- When managed internal Darwinian pro- formation in a managed Darwinian fashion. cessing culminates in an output structure, its Under these conditions, the information trans- salient features can be stored in long-term mitted across generations of hominids in coali- memory for future retrieval and use. Such uses tions will, perforce, be subject to direct and include as a starting point (a "primitive") for indirect selection. future rounds of Darwinian processing or, al- Understanding the power of this intersec- ternatively, as a structure to control selection tion of the coalitional enforcement hypothesis during such processing. On this theory of with theories of mind can be improved by in- minds, the use of such primitives at the begin- spection from the somewhat different perspec- ning of analysis of novel situations is responsi- tive that follows. All animal minds-including ble for what we subjectively experience as ana- those of the hominids immediately ancestral logical thought. to incipient Homo and of contemporary hu- This class of theories provides a robust alter- mans-consist of genetically designed systems native to many trivial or formally magical ex- for managed internal Darwinian processing of planations for mental events. A theory of this mental information structures. For nonhu- form appears likely to be fundamentally cor- man animals, the resulting mature mental in- rect-though, as yet, mechanistic detail re- formation structures generally perish with the mains largely unclear. For readers not familiar individual animal, analogously to its mature with such theories of mind, it is most illuminat- antibody repertoire-only the genetic design ing to consider the analogy between such sys- information for the hardware supporting the tems and the vertebrate immune system, as system itself is under conventional Darwinian originally pointed out byJeme (1967; reviewed selection and is transmitted genetically to off- in Plotkin 1993). Both systems apparently gen- spring, analogously to the design information erate complex mature repertoires-of anti- for immune system hardware. bodies or of mental information structures-on With the emergence and refinement of the basis of managed internal Darwinian pro- large scale tertiary mutualistic exchange of in- cesses. formation between nonclose kin, however, Once the honest communication problem the mature products of these separate Darwin- is solved by the coalitional enforcement hy- ian processing systems (minds) can be trans- pothesis {4c), this theory of minds predicts, in mitted to other minds indefinitely. Thus, such a straightforward fashion, the emergence of a mature information structures are now poten- domain with all the relevant properties of the tially immortal. Moreover, such structures in- extragenetic domain described above. Most evitably undergo new rounds of internal Dar- generally, the minds of contemporary verte- winian processing in each new mind to which brates are the products of hundreds of mil- they are transmitted. In the course of routine lions of years of selection for the machinery internal Darwinian processing, each new mind supporting managed Darwinian information will generate potentially novel variants of the processing and the use of the products of such transmitted information structure and subject processing to control and organize behavior. these variants to selection against this mind's Solution of the cooperation problem and the partially idiosyncratic informational repertoire. consequent emergence of large scale informa- Many rounds of such transmission and re- tion exchange in incipient Homo does not cre- finement will produce potentially vast im- ate an operationally new kind of mind. Rather, provements in congruence between such characteristically powerful human minds structures and salient elements of the physical emerge under these conditions as a result of environment, as well as internally among such joining highly derived, but formerly relatively information structures themselves. On the co- isolated, vertebrate minds into extended se- alitional enforcement hypothesis, this effect is rial processing arrays with the emergence of the source of the unique power of human hominid cooperation. minds. 148 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

A secondary implication of these considera- extragenetic information currently held by an tions will also be important later {6}. Specifi- individual-is created by sampling this pool. cally, the achievable quality of extragenetic Individual hominids contribute to the pool to information structures will ultimately be depen- the extent that elements of their extrageno- dent on the number of independent rounds of types are effectively communicated to other refinement, and thus on the effective size and coalition members. Elements of such extrage- temporal persistence of cooperative hominid netic information pools are expected to be- coalitions. Indeed, since refined information come increasingly coadapted with time-gen- structures can be used subsequently as primi- erally analogously to coadaptation of alleles tives or to impose indirect selection, these co- within a local gene pool. alition-size and persistence effects are likely to Third, emergence and refinement of coa- be exponential or quasi-exponential. litional enforcement supports adaptive indi- It is important to emphasize again two cru- vidual specialization-an example of tertiary cial points. First, the cooperative information mutualism. Thus, individual extragenotypes processing and exchange described immedi- within cooperative hominid coalitions can ately above is expected to be a sustainable ad- contain some distinct elements. Under these aptation only in the context of enforcing- conditions each member of a hominid coali- and, thus, cooperative-coalitions. Second, tion has some access to some of the adaptive long-term memory apparently involves struc- benefits of extragenetic information held by tural changes in neural connections (see Gaz- other coalition members. Therefore, the size zaniga 1997, and references therein). Thus, of extragenetic information pools will gener- extragenetic information is expected to con- ally increase with increasing size of coopera- tribute to the structural design of mature hu- tive coalitions. This increase in the pool size man brains fully as much as does genetic de- and the related effect of coalition size on the sign information. quality of extragenetic information discussed above {4E} become crucially important in be- 4F. EXTRAGENETIC INFORMATION: haviorally modern humans {6}. SECOND ORDER REFINEMENTS Fourth, extragenetic information includes First, it is crucial to recognize that selection information supporting what we subjectively ex- on extragenetic information is expected to oc- perience as conscious beliefs about the world. cur largely or exclusively in the context of However, it also includes far larger amounts hominid coalitions. Among other implications, of information that we are not always explicitly indirect selection will reflect the coercive aware of. For example, the superiority of the power of these coalitions {also see 7B}. More human capacity to draw elementary causal formally, extragenetic information structures inferences from routine daily experience ap- representing both adaptive cooperative op- parently results from extragenetic design in- portunities and the likely consequences of co- formation acquired during early childhood alitional enforcement actions will be subject development. More generally, most managed to high instantaneous levels of direct selec- Darwinian processing of extragenetic infor- tion. These structures, in turn, will impose in- mation {4E} is expected to be done without direct selection on extragenetic information conscious awareness. This is crucial. The quan- during managed Darwinian processing that tity and nature of extragenetic information is leads to specific behaviors. Moreover, there expected to be largely inaccessible to assess- will be strong direct selection for genetic and ment by introspection. Understanding must extragenetic devices sustaining transmission be approached in other ways, such as examina- to and reception among coalition members of tion of the effects of extragenetic information such extragenetic representations of the co- on behavior. operative/coercive environment {4G}. Fifth, in a related point, extragenetic design Second, the sum of all extragenetic informa- information ultimately came to support an tion held by the members of a hominid coalition enormous array of adaptive cognitive, behav- is defined to be the coalition's extrageneticinfor- ioral and material devices in Homo.Such devices mation pool. An individual's extragenotype-all are quite complex, and expected to commonly JUNE 1999 HUMAN UNIQUENESS 149 involve pleiotropic/combinatorial contribu- times be parasitized by other members of his tions from multiple elements of extragenetic coalition, and his fitness will be reduced. information acquired serially in an extended Among other consequences, he may experi- process of accretion of design. Moreover, ence "pain" or "displeasure" as a result of rela- complex devices designed in this way are fre- tive deprivation. These subjective experiences quently opaque to direct "reverse engineer- reflect the functioning of genetic and extrage- ing." [Recall that reverse engineering of devel- netic devices that impose indirect selection on opmental or physiological devices designed by mental information-including extragenetic genetic information is also extremely difficult, information. His picture of the coercive capa- for precisely analogous reasons.] bilities of his coalition may therefore change Speculation about human minds/brains has as a result of this indirect selection. Moreover, been a deeply confused and contentious en- his persistence and contribution of extrage- deavor for at least the last 3000 years or so (see, netic information to his coalition's pool will be for example, Searle 1984; Dennett 1995). On threatened by the consequences of his being the theory proposed here, much of this confu- exploited, and his extragenetic informational sion results from failure to distinguish between repertoire will thereby also be vulnerable to relatively simplereplicating extragenetic design direct selection. information itself and its tremendously com- Conversely, if his picture underestimates the plex, diversephenotypic consequences. Among coercive threat of his coalition, he will some- these consequences are no doubt processes we times attempt parasitic behavior toward other subjectively experience as characteristically coalition members that provoke painftil and human levels of "rational thought," "intention- potentially lethal retaliatory enforcement ac- ality," "moral judgment" and "consciousness." tions. Analogously to the case above, the extragenetic information supporting this "unrealis- 4G. EXTRAGENETIC INFORMATION: tic" picture will be highly vulnerable to both CONCRETE EXAMPLES direct and indirect selection. Now consider the behavior of this young The preceding subsections are necessarily hominid as a participant in coalitional enforce- somewhat formal and abstract. It is therefore ment actions. In the context of expected effects helpful before proceeding to enrich one's in- already described {1B, c}, direct and indirect tuitive grasp of these important issues by con- selection on his extragenetic informational sidering specific examples of how these pro- repertoire will result in his tendency to ac- cesses are expected to work. quire and use the most effective weaponry and Taking a young adult hominid coalition social monitoring devices available, and to ex- member as an example, consider his (or her) ploit these optimally in pursuit of self-interest. behavior as a potential targetfor coalitional en- Self-interest includes punishing parasitic be- forcement. He has acquired during his devel- havior in other coalition members; for exam- opment, from parents and peers, an extensive ple, if he enters an enforcement action with body of extragenetic information, including a inferior weaponry, he is more likely to sustain "picture" of (extragenetic information struc- painful injury or death than if he enters with tures representing) the enforcement/reward superior weaponry. structure of his coalition. This picture controls Given the costs of selection on extragenetic (imposes indirect selection on the mental in- information, we expect the design of genetic formation controlling) his daily behavior. To and extragenetic devices that support the re- the extent that this picture is accurate, he will finement of this information at the lowest at- reap the benefits of tertiary mutualism and tainable cost. For example, humans are ex- avoid punishment at the hands of other coali- pected to be highly adapted to observing (i.e., tion members. Under these circumstances he testing representational information structures is relatively likely to survive and reproduce against) both cooperation and punishment both his genetic and his extragenetic design events affecting other coalition members. Such information. testing would allow the young hominid of our In contrast, if his picture overestimates the example to refine his picture of his coalitional coercive threat from his coalition, he will some- environment rapidly and at relatively low cost. 150 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

In this context it is most striking to consider dent on and limited by extragenetic design in- patterns in entertainment. For example, most formation. In turn, the quantity and quality of of the highest-grossing films of the contempo- this information is absolutely limited by the rary era and many of the best-selling novels effective size and temporal persistence of the and most-watched television programs appar- coalitions in which we develop {4E-F). Thus, ently cater to predicted enforcement "voyeur- when humans develop in small or historically ism." A central thread in these plots is that unstable coalitions, their minds are limited; "good guys" generally inflict violent punish- on the other hand, minds that develop in the ment-often using state-of-the-art or even "fu- context of larger, more stable coalitions are turistic" weaponry and technique-on "bad potentially correspondingly more powerful. guys." Another large class of such entertain- Though this conclusiorn tends to be obscured ment products explores acts or lives of self- by our universal individual intellectual conceit, sacrifice, kindness or altruism, and apparently it nonetheless appears to be an inescapable caters to and/or seeks to manipulate the pre- implication of the coalitional enforcement hy- dicted cooperation voyeurism. pothesis. Full understanding of elements of the discussion of human history to follow {6} 4H. REPRISE requires that this implication of the theory be The following three general implications of clearly grasped. the theory of extragenetic information developed in this section are important to have 5. SELECTED EMPIRICAL EVIDENCE clearly in mind. SA. HOMINID PALEONTOLOGY First, the theory predicts that individual In this and the following sections {6 and 7}, hominids-including contemporary humans- selected examples of the extensive empirical will be highly adapted both to maximal exploi- support for the coalitional enforcement hy- tation of the coalitional enforcement tools pothesis will be reviewed. One of the most available to them, and to accurate assessment compelling of these is the capacity of the the- of the resulting enforcement environments in ory to account parsimoniously for the com- which they live. Thus, for example, when a plex set of events reflected in the hominid fos- fundamentally new weapon technology per- sil record, mits substantial expansion of enforcement ef- The coalitional enforcemnent hypothesis ex- ficiency, the theory predicts that a correspond- plicitly predicts that initial adaptations to im- ing increase in social cooperation will follow proved weapon competence-throwing and rapidly-within one or a few human genera- clubbing-should emerge very rapidly and si- tions. This is a robust, testable prediction of multaneously with adaptations to increased the theory, and I return to it in detail in sec- social cooperation and to the generation and tion 6. use of extragenetic information. The fossil rec- Second, one of the primary objections to ord strongly supports this prediction. Darwinian theories of human cultural evolu- The significance of the fossil record is more tion has been the observation that a significant easily appreciated in light of contemporary fraction of human behaviors have no apparent human anatomy. The coalitional enforce- direct adaptive relationship to the physical en- ment hypothesis predicts that contemporary vironment. However, if the coercive human humans are the products of some 2 million coalition is itself a major element of the selec- years of selection for competence in the use tive environment, and if coalitions sometimes of projectile and clubbing weapons. Humans impose "arbitrary" constraints (designed by should thus have unique skills reflecting this extragenetic information) on their members, history, and we do. Anyone who has watched these formerly mysterious behaviors become an American baseball game is implicitly aware fully interpretable on a Darwinian hypothesis. of this. Humans can throw a 90 mile-per-hour {See subsection 6E for discussion of a major fastball (projectile) with remarkable accuracy, source of such "arbitrary"constraints.} and hit such a fastball on the fly with a bat Third, even the most elementary capacities (club). As predicted, this virtuosity is unique of human minds are, by hypothesis, depen- to humans among all known lineages, living JUNE 1999 HUMAN UNIQUENESS 151 or extinct. Although other primates can throw mained obscure, however. The coalitional en- and club, they do so with much less force, forcement hypothesis predicts the observed much less control, or both (see, for example, unique relationship between this virtuosity Goodall 1964; Plooij 1978). and the development of a social adaptation Moreover, the extent of this virtuosity is involving extensive cooperation between non- probably even greater than it appears on the close relatives, with its diverse, dramatic conse- basis of humans living in contemporary com- quences {1}. plex civilizations. As Barbara Isaac (1987) has With these considerations in mind, I turn documented, there is good reason to believe to the illuminating fossil record of Homo and that humans in less complex societies who its immediate ancestors. First, the hands of the practice intensively from an early age can australopithecines who immediately preceded throw simple projectiles with spectacular ac- ancestral Homo underwent changes from the curacy, momentum and frequency. presumptive last common ancestor with chimps As expected, this virtuosity is supported by (Aiello and Dean 1990; Susman 1994; Marzke skeletal adaptations. For example, while the 1997). These are interpretable as limited ad- contemporary human hand has clearly been aptation to the use of clubbing and projectile redesigned under selection for diverse adap- weapons-again, possibly for improved preda- tive capabilities, among these are certainly tor defense. However, these adaptations are throwing and clubbing (compare Napier 1962 significantly short of those in the contempo- with Marzke 1983, 1997). Further, the con- rary human hand. temporary human lower skeleton-legs and Second, by hypothesis, these capabilities supporting structures-has clearly been rede- improved sufficiently to support rudimentary signed for increased efficiency of bipedal loco- coalitional enforcement in at least the local motion (Klein 1989; Aiello and Dean 1990); australopithecine population immediately an- however, this was likely not the sole relevant cestral to incipient Homo. adaptive priority. Third, with the origin of Homo, dramatic Specifically, Fifer (1987) has pointed out that skeletal redesign followed. The details of these some details of human leg structure strongly changes represent strong evidence for the co- suggest that throwing was also an important alitional enforcement hypothesis. Within less adaptive priority. These properties include the than several hundred thousand years of the details of the locking apparatus of the knee, emergence of incipient Homo, massively rede- and the relative massiveness of human legs in signed animals classified as Homo ergaster/erectus comparison to legs thought to be adapted ex- dominate the fossil record. These animals have clusively to bipedal locomotion, such as in the essentially modern postcranial skeletons, with ostrich. These and related properties allow the implication that they could likely throw the contemporary human posterior skeleton and club with skill approaching that of con- to act as an effective "launching platform" for temporary humans (reviewed in Walker 1993). accurate, high-momentum throwing. Note that Simultaneously, these animals also display sub- these same properties also support more effec- stantially increased cranial volume, and are tive clubbing. thought to have had an extended childhood Analyses of hominid skeletal adaptations to (secondary altriciality) (reviewed in Walker throwing/clubbing have been widely under- 1993; Leakey and Lewin 1992; Tattersall 1995; appreciated by paleontologists and physical Walker and Shipman 1996; Stanley 1996). anthropologists because there was no theoret- These latter two properties would be ex- ical framework suggesting that these activities pected to be produced by genetic adaptation were important. That has now changed, and to substantially increased social cooperation more extensive specialist attention to this is- and to the use of extragenetic information. sue is definitely warranted. Specifically, expanded cranial volume reflects, Contemporary human virtuosity in throw- in large part, genetic adaptation to the re- ing has long been recognized empirically ceipt, use and transmission of extragenetic in- (Darlington 1975; Calvin 1983; Fifer 1987; formation in contemporary humans, and it Isaac 1987). Its theoretical significance has re- seems likely to have had the same function in 152 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74 early Homo. Moreover, secondary altriciality Motivation is now clear, and future intensive extends the childhood period of efficient so- study of this issue will be of great interest. cial learning, thus supporting the transmis- In spite of this limitation, several currently sion of larger amounts of extragenetic infor- available sets of observations are noteworthy. mation in contemporary humans and, again, First, the cranial vault underwent a remark- it seems likely to have had the same function able thickening, apparently precisely at the or- in early Homo. Further, this extendedjuvenile igin of Homo (Klein 1989). This is consistent dependence is sustainable in contemporary with the predicted new selection for resistance humans only because of our substantially in- to weapon injury at this time. [Activity-level creased levels of social cooperation that allows effects are not in themselves necessarily suffi- for reliable support of vulnerable juveniles cient to account for this massive thickening in and, again, this seems certain to have been early Homo (Lieberman 1997).] Second, the true in early Homo as well. pattern of damage to some Lower and Middle Fourth, the fossil record of the animals be- Paleolithic adult hominid fossils is interpret- tween the australopithecines and the exten- able in various ways, including that they may sively redesigned Homo ergaster/erectusis gener- have resulted from defensive wounds occurring ally consistent with the expectations of the during intraspecific violence (Trinkaus 1986). coalitional enforcement hypothesis. This re- In view of the lack of evidence for organized cord is as yet too fragmentary to be decisively intergroup warfare in premodern humans informative, however (Tattersal 1995; Stanley (Keeley 1996), these observations are consistent 1996). Nonetheless, it is noteworthy that these with the coalitional enforcement hypothesis. incompletely understood transitional animals Assessment is somewhat easier for the more apparently left large numbers of stones (ma- abundant younger prehistoric materials. Sig- nuports) in their tool assemblages that could nificant fractions of skeletal remains from re- be used as thrown projectiles but are poor sub- cent prehistoric sites show signs of death by strates for stone tool manufacture (Isaac 1984; homicide under conditions suggesting intra- Potts 1988). This suggests, as the coalitional en- group violence. For example, executions by forcement hypothesis predicts, that these ani- clubbing and projectile weapons are strongly mals made systematic use of high-momentum suggested by several burials at Cahokia in the thrown projectiles for the first time in history. American Midwest (around 1200 AD; Pauketat In summary, the contemporary human skel- 1994). Moreover, orderly prehistoric grave- eton has been extensively redesigned to sup- yard burials of homicide victims are widely ob- port both throwing and clubbing, and the use served (see, for example, Walker 1989; Close of extragenetic information. Further, elon- and Wendorf 1990). These are consistentwith gated human juvenile development requires intragroup violence, although other interpre- substantially expanded social cooperation. tations are also possible. This suite of adaptations arises simultaneously Extensive and relatively straightforward data and relatively rapidly in incipient and early are available from the historical era. These Homo,precisely as the coalitional enforcement clearly indicate that death at the hands of hypothesis predicts. members of one's own coalition (band, tribe, chiefdom or state) is quantitatively important. 5B. DIRECT EVIDENCE FOR Two examples are illustrative. First, Lee's (1979) ENFORCEMENT ACTIONS study of the !Kung San indicates a rate of intra- The theory predicts that the most impor- band homicide of about 30/100,000 person- tant impact of weapons on human evolution years, or about 1% per generation. [In con- was through coalitional enforcement. If this is trast, the San historically experienced much the case, serious injury and death at the hands lower levels of extraband homicide (Lee 1979).] of fellow coalition members should have been Moreover, a significant fraction of these relatively common throughout the history of deaths can be described as coalitional enforce- the species. This possibility has received lim- ment. For example, in several cases, unusually ited specialist attention because of the absence aggressive individuals were killed by arrows of a theoretical motivation for investigation. launched by a group of fellow band members. JUNE 1999 HUMAN UNIQUENESS 153

Second, Scully (1997a,b) found that killing for tertiary mutualism {1A-1c; 4E-F}. However, of citizens by their own states (secondary coali- this tendency to increased coalition size is ex- tions; see subsection 6B) was extensive. For expected to be limited ultimately. ample, in the 20th century at least 170 million Specifically, with the emergence of rudi- (and possibly as many as 360 million) people mentary coalitional enforcement, there will have been killed by their own governments, be strong selection for individuals to monitor as opposed to the 42 million who died in the not only their own interactions with other co- massive wars of the century. alition members, but also the interactions be- The magnitude of this effect can be better tween all other pairs of coalition members {1c; appreciated by summarizing Lee's (1979) and 4F,G}. This substantially increases individual Scully's (1997a,b) data as follows: the fraction fitness by allowing extensive coordination of modern humans killed at the hands of their among punishers, thus producing the expo- own coalitions ranges from about 1% for the nential risk reduction discussed in Ic. More- !Kung San to 8.9% (13th Century), 4.7% (17th over, it allows an individual to punish without Century), 3.7% (19th Century) and 7.3% first being individually parasitized. (20th Century) for citizens of state-level civili- As a result, the individual cognitive burden zations. Moreover, such fractions can be much of coalitional enforcement increases as a quasi- higher on a local, episodic basis. For example, exponential function of coalition size. [The approximately one-third of all Cambodians precise relationship is equivalent to the num- were killed between 1975 and 1979 during the ber of unique pairs (p) that can be formed Khmer Rouge era (Scully 1997a). from a coalition of size n, which is given by Notice that death at the hands of members the relation p= n!/2[(n- 2)!], which reduces to of one's own coalition is much more likely n(n- 1)72. This function has a continuously in- than death in other ways-including by dis- creasing slope.] Coalition size is therefore ex- ease or in war-to be "directionally selective" pected to increase with time, but only to the with respect to social behavior. That is, the point where further increase in the cognitive probability of such death is likely to be contin- burden of monitoring becomes unsustaina- gent on earlier social cooperation/parasitism. ble, given physiological, anatomical and devel- In summary, although mortality data are opmental constraints on brain development. fragmentary, they nonetheless support, or in {See section 6 for discussion of the emergence some cases are consistent with, the prediction of the large organizational units seen in con- of the coalitional enforcement hypothesis that temporary humans.} death at the hands of one's own coalition is Once this size limit is closely approached, relatively common. In particular, the fraction continued refinement of the social adaptation of modern humans killed by members of their is expected to occur, but to produce increas- own coalitions is large enough to represent a ing numbers and efficiency of tertiary mutual- very strong source of selection when iterated istic behaviors rather than further increases in over the some 100,000 generations since the coalition size. I will refer to such coalitions as origin of Homo. On the coalitional enforce- primary coalitions. ment hypothesis, the directional component It is not obvious a priori what this size limit of this selection is central to the evolution of might be. However, in pursuit of a different human uniqueness. theory for the origin of human social behavior, Dunbar and collaborators have carried 5c. SIZE OF HUMAN COALITIONS out an important series of empirical investiga- To support evaluation of the additional evi- tions that suggest that this number is of the dence to be discussed below, a quantitative order of 150 individuals (see Dunbar 1997 for treatment of human coalition size is necessary. a recent review of this work). [Note that this The theory predicts that coalition size should number generally refers to the effective size of increase during the early stages of the emer- the group of individuals with which a focal in- gence of Homo. Larger coalitions substantially dividual might cooperate over time-for ex- decrease the individual cost of coalitional en- ample, through a seasonal round-rather than forcement and allow additional opportunities the size of a routine daily aggregate.] 154 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

In summary, on the coalitional enforce- emerges some of the most persuasive support ment hypothesis, the evolution of a highly de- for the coalitional enforcement hypothesis. rived adaptation to extensive cooperation One of the most important observations of within primary coalitions was the central pro- contemporary paleontology and archaeology cess of evolutionary change during the some 2 is the human "cognitive explosion" that begins million years between the emergence of Homo with the Upper Paleolithic Revolution at about and the emergence of behaviorally modern 40,000-50,000 years ago and extends through humans about 40,000 years ago. Various ge- to the present (reviewed Roebroeks et al. netically designed novelties of modern hu- 1988; Trinkaus 1989; Mellars and Stringer mans, such as language competence and brain 1989; Mellars 1990; Leakey and Lewin 1992; enlargement/remodeling, all evolved in this Stringer and Gamble 1993; Wenke 1990; Gam- context and, by hypothesis, were dependent ble 1993; Roberts 1993; Sofer 1994; Tattersal effects of coalitional enforcement. 1995). This is associated with relatively abrupt emergence in the record of extensive material 5D. EARLY HOMINID WEAPONS exchange, art, material symbolism and in- Formally, enforcement in a coalition of creasingly complex functional technologies, about 150 individuals requires weapons that and the ongoing refinement of all these. can kill/injure from a range of some 20 to 30 Conspicuously, it is widely recognized that meters, allowing a potential perimeter of fire the fossil record shows no evidence for a hu- of perhaps 130 to 190 meters. Moreover, in the man genetic revolution corresponding to this context of multipleindividuals participating in behavioral revolution. On the one hand, ana- coalitional enforcement, a relatively low prob- tomically relatively modern humans existed ability of inflicting disabling injury or death for at least 50,000-70,000 years before the Up- per individual projectile throw is sufficient. per Paleolithic Revolution. On the other hand, [For computational and heuristic simplicity, I subtle change in the human skeleton-espe- will assume throughout that enforcement risk cially reduced robustness-has been more or is being equally distributed. Of course, this is less continuous through the present (Mellars unlikely in practice and the theory does not and Stringer 1989; Mellars 1990; Sofer 1994; require it. Rather, the theory merely requires Tattersall 1995). [Anatomically modern hu- that risk be sufficiently broadly distributed to mans before the Upper Paleolithic Revolution permit sustainable coalitional enforcement.] are conventionally designated early moderns These requirements are well within the and those after are termed late modernsor be- capabilities of early hominid weapons. For ex- haviorally modernhumans.] ample, a 400-gram stone manuport (about the The theoretical problem presented by these mass of an American baseball) thrown from 20 remarkable features of hominid history is in- meters (about the distance from the pitcher's completely or implausibly resolved by previously mound to home on a baseball diamond) by an proposed models for the origin of human experienced hominid would have a significant uniqueness. In contrast, the coalitional en- probability of inflicting serious injury. Fur- forcement hypothesis directly predicts these ther, a well-thrown simple wooden spear would features-including their abruptness-as well likely allow a kill probability per throw ade- as diverse additional details of the behaviorally quate for coalitional enforcement out to ranges modern human record, as discussed in detail of some 30 meters. below 16c-E}. Before proceeding, it is important to understand the constraints the theory imposes. Spe- 6. EMERGENCE OF BEHAVIORALLY cifically, the extent of human coalitional coop- MODERN HUMANS eration at all levels is expected to be strictly 6A. CONTEXT determined by the properties of coalitional The material record of behaviorally mod- enforcement. Thus, factors that affect coali- ern humans (the last 40,000 years or so) is sub- tional enforcement-weaponry performance stantially more extensive than for the preced- and social monitoring efficiency-will consti- ing history of Homo. From this detailed record tute an aggregate independentvariable by which JUNE 1999 HUMAN UNIQUENESS 155 the extent and scope of human cooperation, coalitional enforcement hypothesis predicts up to and including the contemporary state, the emergence of extensive cooperation be- will be strictly limited {1; 4E-G}. Moreover, in- tweenmembers of different primary coalitions. creases in social complexity are expected to During the ongoing refinement of the human ensue rapidly when this constraint is elevated cooperative adaptation at the level of primary by improvements in weaponry and monitor- coalitions-from perhaps 2 million to some ing {4E-G). 40,000 years ago-several factors, including There are other potential independent vari- reduced individual enforcement cost and in- ables here, including human population den- creased hunting/scavenging efficiency, would sity and ecological carrying capacity, of course. have continuously selected for improvement However, the cooperative adaptations charac- in projectile weaponry. As long as such im- teristic of behaviorally modern humans-by provements did not dramatically extend the hypothesis, allowed and limited by coalitional effective range of projectile weapons theywould enforcement-dramatically alter both ecolog- have had only the effect of increasing the level ical carrying capacity and the effects of popu- of cooperation within primary coalitions. lation density. Therefore, coalitional enforce- In early modern humans, however, who by ment efficiency is expected to be the single hypothesis were already highly adapted to co- most important independent variable. alitional enforcement, a critical range thresh- The theory explicitly predicts that the level old exists. At the point where projectile weapon of modern human coalitional cooperation range becomes great enough that the mem- (social complexity) in nonmarginal habitats bers of multiple primary coalitions can share should correlate robustly in space and time equally in the cost of punishment of a parasitic with the weaponry and social monitoring tech- act by an "outlaw" primary coalition, tertiary nologies supporting coalitional enforcement. mutualism between primary coalitions will There is apparently no cogent theoretical al- emerge. ternative to this relationship. It is essential that Analogously to the case of enforcement this critical point is grasped if the remainder withinprimary coalitions-recall especially Lan- of this paper is to be understood. chester's Square Law {lc}-there will then be strong selection for rapid refinement of this 6B. TRANSITION TO MODERNITY: THEORY capability once it emerges. The resulting ad- The theory specifically predicts the follow- aptations will include further improvements ing evolutionary sequence. Based on consider- in projectile weapon technologies and social ations above {1, 5cl, we expect emergence of monitoring strategies operating among pri- early human social organization in which indi- mary coalitions. These adaptations are ex- viduals are highly adapted to life within exten- pected to be largely controlled by extragenetic sively cooperative primary coalitions of modest information in the expanded, high quality size. The relationship among different pri- pools of these enlarged cc;alitions {4E-G}. mary coalitions is generally expected to be for- Because of the relative difficulty of monitor- mally similar to the relationship between indi- ing at the levels of secondary coalitions {5c}, viduals in a relatively nonsocial animal species. human cooperation on a day-to-day basis is ex- Members of two different primary coali- pected to remain primarily focused on the pri- tions are expected to show only the limited mary coalition-as it arguably does through to cooperation consistent with kin-selected be- the present moment. Nonetheless, the adaptive havior and primary and secondary mutualism. advantages of even limited tertiary mutualism They will engage in no tertiary mutualism. among members of different primary coali- While such modest cooperation would likely tions are expected to be crucial. Collectively, have had significant effects-for example, in these effects should produce an explosive re- the form of mate exchange-it is much less finement of tertiary mutualism among mem- than the level of cooperation often seen be- bers of different primary coalitions. tween members of different primary coali- Thus, on the coalitional enforcement hy- tions in contemporary humans. pothesis, tertiary mutualism among members From this level of organization, in turn, the of different primary coalitions, with its diverse 156 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74 consequences, is the behaviorally modern hu- haviorally modern humans as they spread man social adaptation. The dramatically rapid across the globe (see especially Gamble 1993; rise and ongoing refinement of this adaption see also Marks 1993; Sofer 1994; Shea 1997, is likewise predicted by the theory. 1998; Knecht 1997). I will refer to the resulting social unit in Light bolts are shafts that carry small, sharp, which members of different primary coalitions hafted points (Knecht 1997). Such points can engage in tertiary mutualism as a seconda co have great penetrating power without high alition. Some of the extensive empirical sup- projectile mass (Ellis 1997). The effective range port for this view of the origin and nature of of such weapons is significantly increased over behaviorally modern humans is reviewed in that of Lower and Middle Paleolithic projec- the remainder of this section. tiles for two related reasons. On the one hand, lighter bolts can simply be thrown farther. On 6c. WEAPONRY AND THE TRANSITION the other hand, an individual can carry a num- TO MODERNITY ber of light bolts, in contrast with only one or In vies of te above considerations, the cover few heavier Middle Paleolithic spears that alitional enforcement hypothesis predicts that would he caried. [See Thieme 1997 and Den- weaponry range and performance should cornell 1997 for an example of such heavy spears, relate extensively with the degree of social co- and Shea 1997; 1998 for reviews of these is- operation among behaviorally modern hu- sues.] This supports greater effective range in mans. A remarkably robust correlation is in coalitional enforcement actions by allowing a fact observed, and elements of this evidence lower probability of kill or injury per individ- are reviewed in this and the following subsec- ual throw. tion. The correlation beween novel social The effective range of hand-thrown light monitoring devices and behaxiorally modern bolts is estimated to be of the order of 60 meters human cooperation is discussed in subsec- (Knecht 1997; Hutchings and Bruchert 1997, tion 6E. and references therein). This corresponds to a The elements of evidence have been se- potental perimeter of fire of about 380 me- lected for their importance or clanty, and are ters-sufficient to support cooperative pun- not selected arbitrarily to support the coali- ishment by at least two primary coalitions {5c1. tional enforcement hypothesis. With the ambig- Thus, this range was apparently sufficient to uous exception of early Mesoamerica discussed cross the threshold for the emergence of sec- below 16D), I am unaware of any significant evi- ondary coalitions. By hypothesis, the enhanced dentiary contradiction of the predicted corre- extragenetic information pools supported by lation between weaponry performance and these initial larger coalitions allowed the de- social complexity throughout the paleonto- velopment of early complex technologies in logical, archaeological and historical records. permissive local ecosystems. These included Recall again that a major adaptive conse- the further improvements in weapon technol- quence of increasing secondary coalition size ogy discussed immediately below. By hypothe- in behaviorally modern humans is expected sis, this transition was the crucial, rate-limiting to be the increased size and qualit of extage- step in dte initiation of the Upper Paleolithic netic information pools that support corre- Revolution. sponding increases in adaptive sophistication Further, the development of the atlad/ 14E-F}. This effect is crucially important to the throwing stick (spear-thrower) in one or more following discussion. of these early secondary coalitions produced The theo predicts that the inifial emer- a substantial increase in light-bolt projectile gence of behaviorally modern humans should range. There is no evidence for this technol- correlate with the development of projectile ogy in or before the late Middle Paleolithic weapons of significantly increased range. The assemblages immediately preceding the Upper development of "light bolt technology" fulfills Paleolithic Revolution in Europe, but it is well this prediction well, and correlates with the represented immediately thereafter (Knecht advent of behavioral modernit; these weap- 1997). Thus, the correlation between the ad- ons ultimately accompanied the earliest be- vent of the light bolt/atlatl technologyand the JUNE 1999 HUMAN UNIQUENESS 157 mature Upper Paleolithic is quite precise. The substantially improve the efficiency of coali- atlatl extends the range of light bolt projec- tional enforcement, and thus cooperation tiles by some two-to-threefold, thus attaining within and the size of secondary coalitions, effective ranges of the order of 100 to 150 me- with ensuing adaptive consequences. An ex- ters (Hutchings and Bruchert 1997). This cor- tensive body of archaeological evidence sup- responds to a potential perimeter of fire from ports this prediction remarkably well. 630 to 940 meters. Note here that cooperation does not imply The light bolt/atlatl technology is predicted equality a priori. Where specialization be- to have substantially increased the potential comes great, as it does in large secondary coali- efficiency and scope of coalitional enforce- tions, differential access to enforcement and ment, resulting in increased secondary coalition social monitoring technologies is probably in- sizes and enlarged, enhanced extragenetic in- evitable. Under these conditions the conflicts formation pools. As expected, substantial ad- of interest that characterize all cooperation ditional technological innovation is associated between nonclose kin will produce significant with the resulting mature Upper Paleolithic. inequality. Thus, the consistent observations Among the various consequences of this was of anthropology and archaeology, that com- the penetration of a greatly expanded range plex human societies are "ranked" societies, of local niches and, ultimately, the first devel- is consistent with the coalitional enforcement opments of plant and animal domestication hypothesis (see Wenke 1990; Pauketat 1994; supporting a number of local horticulturalist Marcus and Flannery 1996 for recent reviews). adaptations (Rindos 1984; Muller 1986;John- To the extent that such adaptations avoid ex- son and Earle 1987; Heiser 1990; Wenke 1990; treme coalitional extortion {JB}, they can be MacNeish 1992; Seemon 1992; Gopher 1994; adaptively stable. Levy 1995). I begin first with the North American record because it is simplest. The bow was appar- 6D. ADVANCED WEAPONRY AND HIGH ently introduced only after the development SOCIAL COMPLEXITY of horticulturaladaptations that involved small- Bow-and-arrow technology was developed scale cultivation of plants by small groups (Blitz one or more times by atlatl-possessing modern 1988; Seemon 1992; Shott 1993, and refer- human coalitions in Eurasia or North Africa, ences below). Moreover, the emergence of in- and was apparently subsequently dispersed tensive agriculturaladaptations-involving culti- throughout Eurasia, Africa and, ultimately, the vation strategies requiring cooperation within Western Hemisphere (Rausing 1967; Blitz 1988; large groups-in this region was relatively re- Farmer 1994). The bow significantly extends cent, and remains are thus overlaid with only light-bolt projectile range. Well-made simple limited amounts of well-understood, histori- (self) bows can project light bolts (arrows) to cally deposited material. ranges of 200 to 250 meters (see, for example, The development of the Mississippian ad- Pope 1923). This corresponds to a potential aptation in the North American Southeast and perimeter of fire of some 1250 to 1570 meters. the Anasazi Pueblo adaptation in the South- This maximal range may be relatively unim- west are particularly illuminating (Muller 1986; portant in hunting (see Hutchings and Bruchert Wymer 1992; Seeman 1992; Shott 1993; Pauke- 1997 for a recent discussion). It is profoundly tat 1994; Pauketat and Emerson 1997; Vivian important to coalitional enforcement, however, 1990; Matson 1991; Sebastian 1992, and refer- where a relatively low individual probability- ences therein). Each of these more complex per-shot of inflicting injury or death is ade- societies was preceded by an extensive pe- quate. Moreover, the bow allows further re- riod-more than 1000 years in the Southwest- duction in bolt mass, with a corresponding in- ern case-of a relatively simple horticultural crease in the number of bolts that can be adaptation in which atlatl-using populations carried. This makes the weapon tactically and grew various crops, including maize. [These strategically much more versatile than the at- correspond to the early Basketmakers of the latl in coalitional enforcement actions. Southwest and the Adena/Hopewell/Late The theory thus predicts that the bow should Woodland cultures of the Southeast.] 158 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

At around 500 to 600 AD in the Southwest 1992). They and their immediate antecedents and 650 to 800 AD in the Southeast, the bow lived in a rich coastal estuarine environment was acquired, apparently from external sources with an unusually high productivity. They thus (Blitz 1988). Within avery brief period in each had an entirely different subsistence adapta- case-of the order of several generations-a tion than the Late Woodland horticulturalists social adaptation based on intensive, large-field immediately to the north. Moreover, the an- cultivation of maize and other Mesoamerican cestors of the Calusa had lived in this estuarine cultigens arose, supporting increased settle- environment for the previous 1,000 years or ment size and density. Within about 200 years so without an obvious increase in social com- in each case, the spectacular flowerings of the plexity. Mississippian and Anasazi Pueblo cultures, As expected, in view of their geographical respectively, were consolidated. Each was com- locations, the ancestors of the Calusa acquired prised of networks of interacting large, seden- the bow at or near the same time as the neigh- tary settlements, extensive long-range material boring Late Woodland ancestors of the Missis- exchange, and elaborate public architecture sippians (Blitz 1988). The Calusa developed and ceremonialism. Each extended over large their agriculture-independent complex chief- areas and encompassed at least tens of thou- dom rapidly after the introduction of the bow, sands of people. and in apparent synchrony with the develop- These event sequences strongly support the ment of an agriculture-dependent complex prediction that introduction of the bow was chiefdom by the neighboring Mississippians. the limiting step in the emergence of these This striking phenomenon is poorly explained extensive cooperative social adaptations. Con- by other theories of the evolution of social spicuously, the presence of a domesticate, complexity, but is predicted by the coalitional maize, which would have permitted agricul- enforcement hypothesis. tural intensification, was not sufficient. This is Third, it is illuminating to compare the Old paradoxical on conventional cultural materi- and New World records, because the bow ap- alist interpretations of human social complex- parently became widespread before plant do- ity (Johnson and Earle 1987). In contrast, it is mestication and the development of horticul- predicted by the coalitional enforcement hy- tural adaptations in the Old World, rather pothesis. Further, the effect of a substantially than afterwards as in the New World (Farmer new hunting technology, the bow, was appar- 1994; Knecht 1997; Bar-Yosef 1998, and refer- ently rapid development of sedentary, agricul- ences therein). I restrict discussion to the de- tural adaptations. This effect is paradoxical on tails of the well-developed record from the Le- the hypothesis that the primary effect of early vant. The abrupt development of the relatively weapons was on hunting. It is predicted by the elaborate preagricultural sedentary Natufian coalitional enforcement hypothesis. adaptation about 11,000 BC apparently corre- Second, while agricultural intensification is lated with the acquisition of the bow by this a common source of material support for large population (Solecki and Solecki 1970; Valla secondary coalitions, it is not the only possibil- 1995; Bar-Yosef1998). This population, in turn, ity. Under opportune local ecological circum- only subsequently domesticated several grains stances, relatively complex societies can be and initiated the Southwestern Asian Agricul- supported by a ready supply of food from the tural Revolution over the ensuing several thou- wild. There are several North American exam- sand years (Bar-Yosef 1998). ples of apparently precise correlation between Thus, the chronological relationships be- acquisition of the bow and dramatic increase tween transition to sedentary population ag- in social complexity in such contexts, as pre- gregates and the domestication of plants was dicted (Reeves 1990; Maschner 1991; Lambert largely or entirely reversed in North America and Walker 1991). and the Levant. In contrast, the acquisition of The Calusa of southwestern Florida, who a fundamentally new projectile weapon tech- developed a complex chiefdom in the absence nology-the bow-and the adoption of seden- of agriculture, provide a particularly compel- tary, complex social adaptations in these two ling example of this (Widmer 1988; Marquardt independent cases correlate well. These corre- JUNE 1999 HUMAN UNIQUENESS 159

lations and failures of correlation are those ex- In closing, I note briefly that the robust cor- pected on the coalitional enforcement hy- relation between weapon performance and pothesis. It is noteworthy here that, on the social complexity predicted by the coalitional coalitional enforcement hypothesis, the chain enforcement hypothesis continues as expected of events initiated by the precocious acquisi- through to the present (Johnson and Earle tion of the bow in Eurasia is likely to have been 1987; Wenke 1990; McNeill 1991; Lechtman ultimately responsible for the contemporary 1993; Roberts 1993; Gies and Gies 1994; Davies global ascendancy of Eurasian cultures. [See 1996; Scarre and Fagan 1997). There is a strik- McNeill (1976, 1982) and Diamond (1997) ing correlation between the acquisition of cast for reviews of contemporary Eurasian cultural bronze weaponry and the rise of "Bronze Age" ascendancy. ] kingdoms throughout Eurasia and, indepen- Fourth, it is currently widely thought that dently, the rise of the Inca kingdom in the An- the bow did not come to Mesoamerica until des. Further, the rise of Mediterranean region after the initial intensive agricultural adapta- "Iron Age" empires correlates well with the ad- tions of the Olmec, Zapotec and other cul- vent of forged iron weaponry, with its lower tures (Coe 1994; Marcus and Flannery 1996). cost and improved availability over bronze. While the theory does not rigorously exclude Moreover, the rise of the high-population- the possibility that some other sufficiently ad- density modern European state and the ensu- vanced weapon technology-such as, some re- ing industrial and scientific revolutions corre- finement of the atlatl-might support such lates with the simultaneous introduction of developments, the robust correlation between efficient cast iron technology and gun pow- acquisition of the bow and increased settle- der-powered projectile weaponry (guns and ment size and stability elsewhere suggests that artillery) into Europe. Lastly, the contem- this should be reinvestigated. porary development of aircraft and rocket Several observations are provocative in this weaponry, with its planetary range, correlates context. For example, a presumptive stone precisely with the unprecedented, ongoing shaft-straightener used in arrow manufacture development of massive international politi- was deposited in the record at about the time cal/economic coalitions. of the first large Olmec settlements (Coe and

Diehl 1980, p 237). This suggests that the bow 6E. SOCIAL MONITORING AND MODERNITY may have been introduced at this time-much The independent variable on which behav- earlier than now assumed. iorally modern human social complexity is Moreover, in the Oaxaca valley there is a predicted to be dependent is a It provocative correlation between the disappear- composite. of ance of stone atlatl dart points and the appear- consists not only projectile weapon perfor- ance of early sedentary settlements (Marcus mance, but also of the properties of social and Flannery 1996). Given their hunting pat- monitoring that regulate coalitional enforce- terns, these sedentary Oaxaca Zapotec were ment {1; 6A}. The theory thus predicts a corre- obviously not without projectile weaponry lation between novel social monitoring de- (Marcus and Flannery 1996). Thus, the impor- vices and increased secondary coalition size, tant possibility exists that they acquired the and extensive correlation is observed. [As bow and initially used hardwood or other pro- above, although only a few specific cases can jectile points that would be difficult to identify be explicitly mentioned here, these cases are in the archaeological record. Future investiga- not chosen with deliberate bias. Specifically, I tion of these issues will be of great interest. am aware of no compelling evidence that con- More generally, while the correlation be- tradicts the predictions of the coalitional en- tween acquisition of the bow and increased forcement hypothesis in this connection.] social complexity has long been suspected on An empirically robust yet theoretically ob- empirical grounds (Blitz 1988; Lambert and scure observation of contemporary archaeol- Walker 1991; Shott 1993), its theoretical sig- ogy and ethnography is the correlation be- nificance has remained unclear. The coali- tween the emergence of large human political tional enforcement hypothesis predicts this structures and of various other elements of relationship in a straightforward fashion. fully modern human behavior, including elab- 160 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74 orate public ceremonialism and construction ated with complex chiefdoms and states (John- of spectacular monumental architecture (John- son and Earle 1987; Wenke 1990); such proj- son and Earle 1987; Wenke 1990; Roberts ects arguably fulfill this requirement. These 1993). The coalitional enforcement hypothe- structures also have mundane function, how- sis accounts for these observations directly. ever, and their causal origin is complex. In Before reviewing specific cases, it is impor- contrast, truly monumental architecture, such tant to appreciate the nature of the monitoring as temples and tombs that have no overtly problem in secondary coalitions. The capacity practical function, and yet within and around of individual modern human cognitive/af- which the exchanges and interactions of sec- fective devices for monitoring cooperation or ondary coalitional cooperation are organized, parasitism is expected to be largely saturated is more telling. These structures apparently by the demands of enforcement at the level have a purely social function and, by hypothe- of primary coalitions {5c}. Thus, in order for sis, a monitoring function. The cross-culturally extensive cooperation at the level of second- universal building of superficially nonfunc- ary coalitions to emerge, specialized monitor- tional, arbitrary monumental structures by ing strategies that do not place extravagant ad- large secondary coalitions has the properties ditional demands on individual minds are expected, if they are produced by extragenetic probably required. Moreover, these strategies information adapted to solving the monitor- would likely come to depend for their design ing problems of these coalitions. on the enhanced extragenetic information In this context, it is striking that massive in- pools of the enlarged (secondary) coalitions creases in arbitrary monumental architecture themselves. and extensive expansion of trade networks Consistent with this last expectation, the (an element of secondary coalitional coopera- emergence of such cooperative adaptations tion) correlate well in a number of different would be commonly associated with only lim- archaeological records. The Hopewell and ited genetic displacement (see, for example, Mississippian cultures of North American Droessler 1981; Bar-Yosef 1998; reviewed in Southeast prehistory are robust examples Cavalli-Sforza et al. 1994). Under these condi- (Muller 1986; Smith 1990; Clay 1992; Pauketat tions, a variety of local adaptations are pre- and Emerson 1997, and references therein). dicted to be idiosyncratic in superficial detail, The central role of massive cathedrals in the but to share a common underlying logic shaped expanding long-range commerce of 12th and by commonalities between late modern hu- 13th century Europe is likewise striking (Bran- man gene pools and the universal selective ner 1969; Fischer 1996). constraints on extragenetic design informa- Second, another strategy to monitor section that supports secondary coalitional coop- ondary coalitional cooperation with little ad- eration. ditional cognitive burden is to require public With these general considerations in mind, (easily monitored) demonstration of compe- a few specific cases and observations will be tence at elaborate, arbitrary ritual. This reconsidered. First, an efficient strategy to moni- quirement has two implications. On the one tor secondary coalitional cooperation with lit- hand, as with monumental architecture, a subtle additional cognitive demand is to require stantial upfront investment of time and mem- public (easily monitored) investment of large ory is required. Moreover, public rituals are amounts of effort and resources in infrastruc- generally designed to elicit (demonstrate) ture; these structures function in tertiary mu- and reenforce learned emotional response to tualism within secondary coalitions. Such in- cooperation at the level of secondary coali- vestment in infrastructure is "upfront," and tions. [See LeDoux (1996) for a discussion of requiring it substantially alters the cost/bene- learned emotional responses.] fit structure of subsequent cooperation. Any Thus, elaborate public ceremonialism has future attempt at parasitic behavior carries the the properties expected if it is produced by severe risk of forfeiture of this large investment. extragenetic information adapted to solving Large public works projects, such as roads the enforcement problems of large secondary and irrigation systems, are universally associ- coalitions. The level or amount of ceremonial JUNE 1999 HUMAN UNIQUENESS 161 behavior in behaviorally modern humans cor- correspondingly enlarged amounts of extra- relates robustly and cross-culturally with the genetic information. The archaeological record size of political structures (secondary coali- provides strong support for this prediction. tions). In contrast, high levels of primary coali- First, although we cannot directly measure tional cooperation occur in modern humans levels of exchange of extragenetic informa- in the nearly complete absence of public cere- tion among prehistoric populations, we can monial behavior (see, for example, Johnson measure them indirectly through material ex- and Earle 1987, and references therein). change recorded in preserved artifact distribu- Social systems that involve cyclical (e.g., sea- tions. These records clearly indicate that earlier in small and sonal) dispersal groups (families populations, including archaic and early mod- primary coalitions) and later reaggregation in ern humans, carried out only very limited and larger groups (secondary coalitions) are espe- localized exchange (Roebroeks et al. 1988; cially illuminating. Elaborate public ceremo- Mellars and Stringer 1989; Mellars 1990; Wenke nialism is generally restricted to the transient 1990; Roberts 1993; Stringer and Gamble periods of reaggregation in secondary coalitions under these conditions, as the coali- 1993; Sofer 1994; Tattersall 1995). In contrast, tional enforcement hypothesis predicts. behaviorally modern humans episodically set Third, relatively recent adaptive technolog- up large exchange networks, often continen- ical changes that depend on written language tal in scope (Muller 1986; Pauketat and Emer- and printing have allowed the expansion of son 1997). monitoring based on bureaucratic record keep- It is quite striking that this pattern of ex- ing and the use of "money." Such strategies change networks begins precisely with the earli- are efficient and become sustainable when co- est mature Upper Paleolithic adaptation (West- alition sizes grow large. In many contexts, in ern Eurasian Aurignacian) and its associated contemporary states these strategies have weaponry innovations {6c}. Moreover, nomi- largely replaced those dependent on individ- nally nonfunctional objects (such as pendant ual investment in public ceremonialism or adornments or religious artifacts) are among monumental architecture. In this connection, the most widely exchanged materials, beginning it will be of interest to see the future effects on with the Aurignacian (White 1993). Among social monitoring of the revolution in elec- other implications, this suggests that some- tronic observation and information exchange thing other than these items-for example, in- and processing that is currently underway. formation-was the functional objective of ex- In of the summary, some most (superfi- change. cially) bizarre, arbitrary behaviors of modern Second, the extensive material exchange humans-including elaborate public ceremo- networks associated with behaviorally modern nialism and construction of extensive monu- humans are usually or always characterized by mental architecture-have precisely the prop- extensive dissemination of specific stylesof elab- erties expected if they are adaptive responses to the special monitoring problems posed by orate public ceremonial behavior and monu- expanding cooperation at the level of large mental architecture (see, for example, Muller secondary coalitions. 1986; Pauketat and Emerson 1997). This observation has two crucial implications. On the 6F. PALEONTOLOGY OF INFORMATION SHARING one hand, it corroborates the claim that extra- The coalitional enforcement hypothesis genetic information is among the items being predicts that the abrupt emergence of com- exchanged. On the other hand, as elaborate plex, behaviorally modern human social orga- public ceremonial behavior and monumental nizations resulted from the transition to and architecture correlate robustly with large sec- refinement of cooperation at the level of secondary coalitions in the ethnographic record ondary coalitions. One of the most important {6E}, it indicates that the expanded informa- adaptive consequences of this development, tion exchange in prehistoric modern humans in turn, is expected to have been the genera- also occurred in the context of such coalitions, tion, refinement and mutualistic exchange of as the theory predicts. 162 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74

6G. MODERNITY: ALTERNATIVE EXPLANATIONS cently acquired with the advent of behavior- The Upper Paleolithic Revolution and the ally modern humans. emergence of behavioral modernity are such Second, recent studies of fossil indicators of dramatic and important events that much at- early human language capability indicate that tention has been devoted to trying to account language is likely to have arisen early in the history of Homo, as the coalitional enforcement for them. One class of theories now widely dis- hypothesis predicts (Kay et al. 1998). These cussed among biologically oriented investi- observations provide no support for the pro- gators invokes a genetic change in the early posal that fundamental language abilities are modern population, resulting in behavioral very recent, though late refinements in the modernity. It has been suggested that such subtleties of linguistic execution remains pos- changes affect intellectual function more gen- sible (see, for example, Lieberman 1991). or more erally, language ability specifically, In overview, on the coalitional enforcement and presumably would require some more or hypothesis, there is currently no substantive less subtle remodeling of the central nervous reason to believe that the ultimate hegemony system (see, for example, Lieberman 1991; of the modern human clade was anything but Bickerton 1995; Mithen 1996; Noble and Da- an historical accident resulting from serendip- vidson 1996). itous local development of light bolt technol- Although it is currently unclear how plausi- ogy. Had this technology been developed in a ble these theories are, they are arbitrary and Neanderthal population instead, our lineage unnecessary on the coalitional enforcement might now be extinct, and descendants of the hypothesis. Specifically, all known elements of Neanderthals might have walked on the moon. brain redesign in Homo are predicted by this hypothesis to be dependent effects of adapta- 6H. CONCLUDING REMARKS tion to coalitional enforcement and its conse- Evidence reviewed here and in section 5 in- quences, rather than one or more of them be- dicates that the coalitional enforcement hy- ing primary causes of human uniqueness. It is pothesis is a robust, general theory capable of useful to note that available empirical evi- accounting for most of the major events dence is more consistent with the coalitional throughout the history of the Homo lineage. enforcement hypothesis than with these alter- The specific examples described in this sec- native theories. tion indicate that the theory accounts in a First, the late Middle Paleolithic Chatelper- straightforward way for the relatively abrupt ronian adaptation among Neanderthals in emergence of behavioral modernity and the southwestern Europe is provocative in this con- ensuing-and continuing-dramatic expan- text. It is identified through a lithic technology sions of human social cooperation. To my that appears to involve substantial borrowing by knowledge, no other currently available the- European Neanderthals from a recently immi- ory provides a comparably direct, parsimoni- grated late modern population (Mellars and ous explanation of these remarkable events. Stringer 1989; Leakey and Lewin 1992; Stringer and Gamble 1993; Tattersall 1995). 7. ADDITIONAL IMPLICATIONS OF THE THEORY These two populations would apparently 7A. THE SELF-DOMESTICATION EFFECT have been separate for some 400,000 to 500,000 Modern human social behavior is remark- years at the time of contact (Krings et al. able not only in its detail, but also in the rapid 1997). Yet, if this interpretation of the Cha- rate at which this highly derived adaptation telperronian culture is correct, both popula- evolved. The coalitional enforcement hypoth- tions were nonetheless highly adapted to the esis predicts this. With the emergence of coali- acquisition and use of extragenetic informational enforcement in incipient Homo, a new, tion. This is poignant support for the predic- intense, directional source of selective pres- tion that human adaptation to acquisition and sure was created. use of extragenetic information is ancient and First, coalitional enforcement permits ex- derived as predicted by the coalitional en- tension of cooperation beyond the limits of forcement hypothesis, rather than being re- close kinship. Thus, cooperative punishers are JUNE 1999 HUMAN UNIQUENESS 163 frequently not deterred by countervailing di- sively similar domestication and self-domesti- rect inclusive fitness interests. They punish ex- cation are in operational detail. clusively on the basis of the target's parasitic behavior, with obvious selective consequences. 7B. HUMAN SOCIAL PSYCHOLOGY Second, tertiary mutualism sustained by co- Various features of human social, ethical alitional enforcement is a substantial adaptive and economic behavior have not found easy advantage to coalition members. Moreover, or straightforward evolutionary explanation. members of established coalitions will gener- The coalitional enforcement hypothesis ap- ally choose new members, where choice exists, parently resolves much of this earlier confu- on the basis of the ability of these new mem- sion, as illustrated in several examples below. bers to contribute substantial service. In con- First, in seminal studies it was pointed out trast, not only will noncooperative individuals that human ethical psychology likely reflects be excluded or punished, but also less valu- the requirements of human social coopera- able or less competent individuals will often tion (see especially Darwin 1871; Waddington be excluded or undersupported, again with 1960; Williams 1966; Trivers 1971; Alexander obvious selective consequences. 1989). However, the details of the selective en- Third, increasing tertiary mutualism, in vironment that produces such psychological turn, increases the capacity of coalition mem- adaptations, the nature of the design informa- bers to reciprocally shield one another from tion that supports them, and the reasons they competing selective environmental forces. Se- are unique to humans have all remained quite lective pressure from the external environ- unclear. The coalitional enforcement hypoth- ment is frequently independent of or even di- esis provides a direct resolution of these issues. rectly antagonistic to the selective pressure For example, moral outrage and guilt, and applied by coalition members. This shielding their tendency to be restricted to circum- can greatly increase the effectiveness of the stances involving groups of well-acquainted directional selection described above. nonkin-that is, potentially enforcing coali- On the coalitional enforcement hypothesis, tions-are predicted. These genetic and ex- modern humans are the descendants of some tragenetic devices are proximate mechanisms 100,000 generations of individuals who both designed to support participation in and avoid- imposed such selection on other hominids ing becoming a target of coalitional enforce- and survived such selection byother hominids. ment, respectively. This conclusion has two important implica- Second, modern humans appear to develop tions. First, modern humans are self-domesti- detailed "theories of mind" of very specific cated animals-an insight suspected on empirical content that apply to other humans (Leslie grounds since Darwin (1871). Contemporary 1994; Premack and Premack 1994). Similarly, human uniqueness arising from coalitional modern humans appear to have a well-devel- enforcement can be productively viewed as oped capacity to detect "cheaters" in social the result of selective breeding at the hands of transactions (Cosmides and Tooby 1992). As unrelated members of the coalitions in which with human social psychology more generally, our ancestors lived for the last 2 million years this important empirical work has yet to pro- or so. duce a compelling theoretical account of the Second, because of the intense, directional evolutionary origin of these capacities. For ex- nature of this process, the rapid rate of evolu- ample, is has remained unclear precisely why tionary change in the Homo lineage is to be ex- such adaptations are unique to humans. pected. These cognitive adaptations and their unique- It is also likely that the highly derived ge- ness to humans are predicted as adaptations netic and extragenetic devices adapted to supporting the social monitoring required for hominid self-domestication subsequently sup- coalitional enforcement. ported the uniquely broad and extensive do- Third, humans commonly show "unexpect- mestication of other organisms by modern edly" high cooperation in economic behavior humans, leading to horticultural and agricul- (Frank 1988; Mansbridge 1990). This is pre- tural adaptations. Note especially how exten- dicted by the coalitional enforcement hypoth- 164 THE QUARTERLYREVIEW OF BIOLOGY VOLUME 74 esis. Specifically, modern human genetic and cooperation among distinct (not identical by extragenetic information shaped by a long his- recent descent) elements of replicating infor- tory of coalitional enforcement is expected to mation with potential conflicts of interest irre- produce individuals designed to participate in spectiveof the level of organization in question. the highly cooperative tertiary mutualism these If this proposal is correct, coalitional en- studies observe. forcement should be an essential, ancient property of the cooperative coalitions of genes 7c. HUMAN REPRODUCTIVEBEHAVIOR making up the complex genomes of contem- Human sexual, family and child-rearing be- porary organisms. This appears to be the case. haviors and properties are unusual among Coalitions of elements of genetic information mammals (Symons 1979; Fisher 1992; Ridley that control cosuppression systems apparently 1993; Buss 1994; Baker 1996, and references have the capacity to actively control ("pun- therein). These include nearly ubiquitous mo- ish") other genetic elements adapted to para- nogamy or mild polygyny, and hidden or oc- sitizing the genomes of sexual organisms (Bing- cult ovulation in females. These behaviors are ham 1997). economically explained by coalitional enforce- Moreover, "divide-and-conquer" strategies ment, as outlined below. can be effective in preventing development of Most generally, one of the central effects large chromosomal segments adapted to para- of coalitional enforcement in this context is sitizing the remainder of the cooperative sex- expected to be reduced variation in reproduc- ual genome (Hurst et al. 1996). The detailed tive success among coalition members. First of properties of known meiotic drive systems all, more specifically, monogamy-and related strongly support this view. The coalitions of mating schemes, including mild polygyny-is genes that produce and control meiotic re- apparently the only adaptively stable mating combination likely evolved, in part, in re- system under such circumstances. This results, sponse to the adaptive requirement for such in part, from the vulnerability of would-be hy- a divide-and-conquer enforcement strategy perpolygynous males to punishment at the (Hurst et al. 1996). hands of coalitions of other males. As expected, these classes of enforcement Second, overt ovulation displays could con- systems appear to be ubiquitous and ancient ceivablybe exploited by females to attempt un- in sexual organisms with complex genomes. usual reproductive success through solicitation Lastly, enforcement is expected to be re- of differential access to material resources quired in order to sustain cooperation within provided by males. Lethal or damaging pun- the extragenetic domain, and between genetic ishment of individual females who pursue and extragenetic information. The indirect se- such strategies by coalitions of competing fe- lection imposed on extragenetic information {4} males might account for the loss of overt ovu- by genetic and extragenetic devices is ex- lation display in modern humans. Alterna- pected to include such enforcement activity. tively, overt ovulation display may have become more costly than adaptive with the advent of 9. CONCLUSION coalitions of potentially sexually aggressive The coalitional enforcement hypothesis pro- males permitted by the emergence of coali- vides a coherent, parsimonious explanation for tional enforcement. human uniqueness. The theory is accessible to verification/falsification by properly designed 8. UNIVERSAL COALITIONALENFORCEMENT empirical investigations in diverse areas, in- In addition to the direct empirical support cluding hominid paleontology, archaeology, for the coalitional enforcement hypothesis anthropology, ethnography, linguistics, eco- {5-7}, a compelling reason to believe that the nomics, sociology, political science, cognitive hypothesis is fundamentally correct and com- science and psychology. plete is that it appears to be general. Specifi- The contemporary social sciences and hu- cally, the logic of coalitional enforcement {1} manities have accumulated enormous, valu- should be universal. Thus, we expect coali- able bodies of descriptive information that tional enforcement to be required to support have led to local, empirical generalizations. JUNE 1999 HUMAN UNIQUENESS 165

However, in contrast to the physical and natu- ACKNOWLEDGMENTS ral sciences, these disciplines have yet to pro- I am extremely grateful to Zuzana Zachar for many duce a meaningful, coherent theoretical ex- helpful discussions throughout the development of planatory structure (critiqued in Tooby and the theory described here. I am further particularly grateful to knowledgeable, cosmopolitan colleague Cosmides 1992). As a result, analytical theory John J. Shea for numerous important discussions. in the humanities and social sciences is fre- Other outstanding colleagues including Sid Strick- quently trivially self-referential. Attempts to land, Elof A. Carlson, Aung Kyaw Chi, David Bern- develop a cogent causal theory of human evo- stein, Rita Nolan, Curtis W. Marean, Murray Sher- man and Fred Weinstein also provided valuable lution, such as that proposed here, will be es- input. I am grateful to Zdenek Zachar for mathe- sential to substantive further progress in these matical advice. Lastly, I am grateful to the editors disciplines. In addition to its theoretical im- and anonymous reviewers for contributing signifi- portance, such progress may have significant cantly to the clarity of the exposition. I have sometimes chosen not to follow specific pieces of advice practical implications, including the support from these various consultants and responsibility of development of more sustainable and hu- for errors of fact, interpretation or judgment is, mane ethical, economic and political systems. therefore, entirely my own.

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