Evolutionary Psychology in the Round Robin Dunbar and Louise Barrett

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CHAPTER 1 Evolutionary psychology in the round Robin Dunbar and Louise Barrett

1.1. Introduction questions that biologists can ask, the other two being questions about function (a teleonomic Although the closing decades of the nineteenth question that is, ultimately, about the genetic con- century witnessed a great deal of interchange sequences of behaviour) and phylogeny (the evo- between psychology and evolutionary biology, lutionary history of how a behaviour came to the hasty departure of James Baldwin from the have its current form). Tinbergen (1963) pointed American psychological scene in 1908 (thanks to out that all four provide appropriate answers to the scandal of being caught in a brothel) trig- the generic question ‘Why does an animal do X?’; gered, for reasons that are more political than sci- all must in the end be answered for a full under- entific, the virtual severance of contact between standing, but each can be asked and answered the two disciplines (Plotkin, 2004). Psychology independently. That is to say, our answer to one became more heavily influenced by its alternate does not necessarily commit us to any particular roots in physiology and the neurosciences, on the answer for any of the others. one hand, and the social sciences, on the other. We want to make two general points in this Evolution played no significant role in psychology chapter. First, the evolutionary approach neces- for the better part of a century. Indeed, the 1950s sarily enjoins us to take a broad disciplinary per- in particular witnessed a somewhat tetchy quarrel spective to our subject matter (which, following between the comparative psychologists (with Heyes (2000), we might refer to as ‘evolutionary their feet firmly planted in behaviourism and an psychology in the round’). Second, an evolution- experimental paradigm) and the ethologists (with ary view does not—and should not—commit us their roots in evolutionary biology, and a focus on to any particular assumptions about the genetic the observational study of an animal’s behaviour determination of behaviour. Indeed, learning, in its natural environment). and by extension cultural transmission, play an In part, this drift away from biology reflected an especially important role in the behaviour of increasing focus within academic psychology on humans, and we will never be able to understand questions of mechanism (with a broad focus on human behaviour without understanding cul- stimulus–response processes, motivation, cogni- ture and the way it influences what humans do. tion and, later, neuropsychology) and develop- These issues are explored in more detail else- ment. For the ethologists, these constituted just where in this volume, but our main concern here two of what eventually came to be known as is to provide a framework within which the ‘Tinbergen’s Four Why’s’—the four kinds of chapters that follow can be understood. 01-Dunbar-Chap01 12/22/06 3:40 PM Page 4

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1.2. Asking the right questions versus ontogenetic (i.e. developmental) questions. Questions about genetic determinism belong to The important consideration in the present con- the realm of ontogeny (how the individual text is that evolutionary (or Darwinian) theory acquires its capacities during the course of devel- provides a framework within which a diverse opment), but the core to an evolutionary approach range of intellectual questions can be integrated. lies in function (questions about the evolution- The significance of this is well illustrated by the ary goal-directedness of these capacities and the role it has played within biology. A century ago, behaviour they make possible). biology consisted of half a dozen or more quite Of course, as an essentially biological question, separate disciplines (anatomy, zoology, botany, the primary focus of functional questions lies in genetics, physiology, microbiology, biochem- how an organism’s behaviour maximizes its istry, etc.) that rarely interacted. The gradual genetic fitness. But the fact that an individual acts acceptance of the theory of evolution as a central so as to maximize its fitness does not mean that organizing principle has made it possible for its behaviour is genetically determined, merely these diverse interest groups to talk to each other that it has a set of genetically inherited motiva- in a common language in a way that had rarely tions (or goal states) that it seeks to satisfy. How been possible in the past. it achieves those goal states will, at least in neu- Our claim here is that an evolutionary approach rologically advanced species, depend on the can and should do the same for psychology. individual’s assessment of the costs and benefits Evolutionary psychology, we argue, is not a new of acting in one way rather than another, given its and separate sub-discipline within psychology, experience of the world. In evolutionary biology, but rather a framework theory that allows psy- every decision is a contingent one that depends chology’s many diverse sub-disciplines to be on the details of the context. That context will integrated into a unitary whole. It is not our obviously include many features of the physical intention to demonstrate this claim here by environment, but in highly social species like showing how different psychological approaches humans it will also include the social environ- could relate more effectively to each other. ment. We return to this point again below. The Rather, our aim is simply to make it clear that a issue here, however, is that the genes that are developmental stance, for example, is not differ- passed on from one generation to another need ent from, or in intellectual opposition to, an be not the genes for a particular behaviour, but evolutionary approach. Rather, an evolutionary may, rather, be the genes for a brain that is large perspective adds to a developmental approach enough, and complex enough, to make the deci- by offering new ways of seeing development, sions about how best to act in order to satisfy prompting novel questions for empirical study, its motivations (thereby maximizing fitness). and, more broadly, allowing developmental psy- Questions about the roles of genes and the envi- chologists to integrate their findings with those ronment in the production of those brains, or of neuropsychologists, cognitive psychologists any other aspect of the system, are of course and others. Life history theory, for example, is interesting, but they remain quite separate, and major feature of contemporary evolutionary are unaffected by the extent to which an individ- ecology, with enormous relevance both to repro- ual can be shown to be maximizing its fitness. ductive decision-making and to development. The issue of ontogeny is, of course, an impor- Yet, its implications have only recently begun to tant one that has been the focus of yet another be explored. Several of the chapters in Section V long-running debate within psychology in par- draw on it in their explorations of different ticular (the so-called nature/nurture debate). aspects of human reproductive behaviour. Biologists have largely accepted, since the 1960s, In this context, it is particularly important to that this distinction is arbitrary and, worse still understand that an evolutionary approach does perhaps, misguided. We cannot separate genes not commit us ipso facto to genetic determinism. from the environment in the simple-minded To assume that it does is to commit a classic cat- way implied by this dichotomy. Both nature and egory mistake by failing to distinguish two of nurture are deeply implicated in the processes of Tinbergen’s Four Why’s—functional questions development, even though it may be possible to 01-Dunbar-Chap01 12/22/06 3:40 PM Page 5

Asking the right questions · 5

discuss the magnitude of the relative contribu- rump on the periphery where they continued to tion of genetic versus environmental effects to focus on somewhat arcane topics like intelligence the differences between individuals. Nonetheless, and personality theory. The rise of evolutionary no aspect of an organism’s biology or psychology ideas in the study of animal behaviour during can be said to be wholly (or even mainly) due to the 1970s (originally in the form of a sub- its genes or the environment in which it grows up. discipline that named itself sociobiology, but The distinction, nonetheless, is important in which later adopted the alternative name behav- one key respect. If we recognize that questions ioural ecology) seems to have been viewed by the about the mechanisms of inheritance are separate naturists as offering something of a bulwark from questions about the evolutionary function against the nurturists, in part at least because it of behaviour, then the way is opened up for the seemed to imply some form of genetic basis for evolutionary study of culture as an important cognition and behaviour. phenomenon in its own right. Self-evidently, cul- This may, in turn, provide us with a way ture depends on learning—specifically the social of articulating the equally fractionated sub- transmission of beliefs or rules of behaviour— disciplines of evolutionary psychology. Since the but learning is simply another mechanism of mid-1990s, evolutionary psychologists have inheritance in the grand evolutionary scheme. been embroiled in what might seem like an Biologists’ perennial focus on genes (and, more internecine war between those whose intellec- recently, DNA) as the mechanism of inheritance tual tradition lay within behavioural ecology is, perhaps, to be expected given their interest in (who sometimes refer to themselves as evolu- the more hard-wired aspects of biology, such tionary anthropologists) and those whose intel- as anatomy. But it is crucial to remember that lectual tradition lay within psychology (who neither Darwin nor Mendel (widely considered originally referred to themselves as Darwinian to be the founding father of genetics) actually psychologists, but later co-opted the term ‘evo- knew anything about genes or DNA. Both the lutionary psychology’). In our view, this dispute Darwinian formula that underpins the theory of is properly seen as being between two of evolution by natural selection and Mendel’s laws Tinbergen’s Four Why’s, specifically between the of inheritance that provide the modus operandi functional approach (represented by the behav- for Darwin’s theory refer only to fidelity of ioural ecologists) and questions about proximate copying (in other words, the similarity or corre- (mainly cognitive) mechanisms (represented by lation between parents and offspring). The evo- the evolutionary psychologists sensu stricto). lutionary consequences work equally well Hence, we endorse the view advocated by Mameli whether the basis of that copying is genetic trans- (Chapter 3) that both together constitute the mission or cultural learning. Of course, there are proper domain of evolutionary psychology some differences in the details of how cultural sensu latto (which he signals with lower case ini- and genetic evolutionary processes work, but tial letters). their role in the bigger scheme of things is suffi- It is equally important to appreciate in this ciently similar to warrant them being treated as respect that an evolutionary perspective does not being equivalent [a point also emphasized by of itself necessarily commit us to the claim that Mameli (Chapter 3) and Laland (Chapter 4); see the mind is entirely organized on modular princi- also Barrett et al., 2000; Dunbar et al., 2005]. ples, even though some have argued trenchantly The fact that the nature/nurture debate has for such a case. Full-scale modularity is just one been so entrenched within psychology for so long of a continuum of possibilities. Indeed, we do perhaps provides us with an explanation for the not doubt that the mind has some degree of recent history of evolutionary psychology. Our modular structure, but it is a purely empirical reading of the history of psychology suggests question as to exactly what form this modularity that, during the 1970s and 1980s, the environ- takes, and how many modules there are. The mentalists (the nurture-folk) began to win the issue cannot be resolved on a priori philosophical nature/nurture debate, especially within devel- grounds, since evolution neither entails modu- opmental psychology—to the point, in fact, larity nor requires it. It may well be that, in the where the nature-folk were reduced to a minority adult, cognition behaves as though it were 01-Dunbar-Chap01 12/22/06 3:40 PM Page 6

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modular, but we have yet to establish whether walking) which have a very ancient origin at the that level of modularity is present at birth (or very root of the hominin tree some 6 MYA develops willy-nilly during childhood, irrespec- (Aiello, 1996). Without these preadaptations, it tive of experience). More importantly, it may would be impossible for modern humans to sus- well be that many of the cognitive scripts that tain the long exhalations that are required for we see in adults behave like modules (may, speech. Were these components of the story more indeed, even be hardwired in neural circuitry), or less important than the social or technological but in fact arise by the switching of cognitive circumstances that created the functional mechanisms from conscious thinking (where a lot demand for communication when language itself of hard cognitive work has to be done ‘up front’) evolved in the late Pleistocene? The answer is not to more automated (subconscious?) processes always as obvious as it might seem. once the phenomenon has been cognitively However, to take such a view does not, of itself, processed often enough during the course of mean that we have to dismiss the evolutionary development (there is, indeed, now neuroimaging psychology sensu stricto approach in its entirety, evidence to support this suggestion). a mistake that has frequently been made by its Although this is an interesting issue in the opponents (many of whom have not always developmental psychology of cognition, we do taken the trouble to investigate its claims at first not see it as an evolutionarily interesting question: hand). There has been much empirical work of evolution is indifferent as to whether the mind considerable worth carried out under this is modular or not, since that is simply a matter rubric, and its value should be recognized. The of history (the stages through which the human reality is that some aspects of our cognition and mind evolved). We can, of course, ask questions physiology do predispose us to behave in certain about the efficiency of the mind’s design, but ways, or at least to have such behaviours as our there is equally no guarantee that evolution will default condition. For us, the more interesting always produce the most efficient design: there issue is the fact that our brains allow us the luxury are too many examples of poor design in biol- of being able to fine tune our behaviour more ogy, of Heath-Robinson adaptations of existing subtly in the light of circumstance: that, after all, components for new purposes for which they is why large brains evolved. In all likelihood, we were not originally designed (a process biolo- probably do come to the world with a set of gists sometimes recognize by the term exapta- default cognitive options, but our cognitive tion). Nor, on this point, do we find the concept capacities—and the processes of cultural trans- of the environment of evolutionary adaptedness mission that these make possible in addition to (EEA) especially convincing or helpful. It may simple trial-and-error learning—allow us the be possible to explain, ex post facto,why modern option of fine tuning our behaviour to the humans and their minds have come to be the circumstances in which we happen to find our- way they are by reference to past circumstances, selves in what are often very subtle ways. Voland but it is rarely possible to identify past circum- (Chapter 28) argues cogently, from a very detailed stances with such precision as to be able to predict review of the evidence from historical demogra- (prospectively) the outcome of any selection phy, for exactly this interpretation. Rather, we take process (Strassman and Dunbar, 1998). Moreover, the view that these disputes are arcane and of the the historical process by which a particular past. We should begin with a clear canvas and set behavioural or cognitive trait is acquired is often about building a more integrated science that so complex and convoluted, it is often hard to draws on all relevant perspectives. know exactly what came when, or which particular time and circumstances played the seminal role. This is well illustrated by the evolution of 1.3. Taking the broad speech and language. In addition to the need for perspective fine motor control, the capacity for speech depends on anatomical capacities associated Although the evolutionary approach was ini- with bipedality (a flattened chest, the freeing of tially applied mainly to questions of cognition the chest wall muscles from the pressure of within psychology [prompting Cosmides and 01-Dunbar-Chap01 12/22/06 3:40 PM Page 7

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Tooby’s (1992) generic design-of-the-mind both as a conduit through which we acquire approach], recent years have witnessed a dra- knowledge about how to behave and as a frame- matic growth in areas traditionally associated work that itself creates many of the costs and with social psychology (for recent overviews, see benefits of social life. Plotkin (Chapter 2) develops Schaller et al., 2006; Forgas et al., in press). this theme in more detail, so we will not elaborate Indeed, there are good grounds for seeing the further on the broader question of the impor- behavioural ecology approach as being tradi- tance of culture. However, one point he makes is tional social psychology with an evolutionary worth emphasizing in more explicit detail because backbone, and the evolutionary psychology sensu it provides the basis for some major new devel- stricto approach as being conventional cognitive opments in evolutionary psychology. And this is psychology with an evolutionary backbone. the fact that humans, like most primates, live in Our view, and the one we have tried to promote large, multilevel societies. here through our choice of contributions, is a For the past four decades or so, evolutionary more balanced one that takes a broader perspec- biologists and behavioural ecologists (and, fol- tive. In selecting topics for inclusion in this vol- lowing their lead, evolutionary psychologists ume, we have endeavoured to give weight to sensu stricto) have tended to view the individual both the central importance of individual topics in isolation, making decisions about how to and the balance across the sub-disciplines that behave in his/her own best interests. The reality, currently constitute evolutionary psychology. of course, is that human (and, indeed, many Our aim has been to work towards a synthesis of mammal and bird) individuals are members of approaches, in the expectation that the range of societies that exist for the individual’s benefit. We topics which can be exposed to scrutiny from an ought not to view an individual as acting in isola- evolutionary perspective will encourage a wider tion in quite the way we have done traditionally range of psychologists to take note of the evolu- because every behavioural decision an individual tionary approach. Our message, more than any- makes has consequences for every other member thing else, is perhaps that the evolutionary of the community within which it is embedded, approach enables us to ask questions that are and those consequences will in due course feed both wide-ranging and interesting: more impor- back on the individual. In actuality, this is noth- tantly, it prompts us to ask questions that are not ing new in behavioural ecology: it is, in effect, the conventionally asked. The fact that evolutionary lesson of Hamilton’s Rule. Although Hamilton’s theory provides a very powerful, well-articu- Rule was originally proposed as an explanation lated and thoroughly developed body of theory for the evolution of altruism [Hamilton’s (1964) has enormous heuristic value because it allows famous theory of kin selection], it has since come us to make strong predictions about how individ- to be seen, rightly, as the fundamental theorem of uals might be expected to behave if a particular behavioural ecology. In a nutshell, Hamilton’s hypothesis is true. The main benefit of evolu- Rule states that a gene for altruism will evolve to tionary theory, therefore, is that it provides a fine stability whenever the benefit to the recipient (in scalpel for hypothesis-testing. terms of number of additional future offspring Despite our insistence on the importance of born), when devalued by the coefficient of relat- intellectual breadth, there is one area that has edness between recipient and altruist, exceeds the remained resolutely on the sidelines of evolu- cost to the altruist (when measured as the num- tionary psychology, namely culture. Though a ber of future offspring lost). While strictly speak- strong research programme developed in the ing just an approximation to Hamilton’s original study of gene–culture co-evolution during the finding (Hamilton termed this ‘neighbour-mod- 1990s, this has remained highly mathematical in ulated fitness’), even so simple a formulation focus, and rather peripheral to the main develop- reminds us that the consequences of one’s actions ments within the broader discipline. Its attention reverberate around the population, and feed back has been focused mainly on the mechanisms on one’s own inclusive fitness (the composite fit- of learning and the dynamics of gene–culture ness of a trait that results from summing one’s co-evolutionary processes. Yet culture plays an personal fitness with the kinship-devalued fit- important role in everyday human behaviour, nesses contributed by everyone else in the wider 01-Dunbar-Chap01 12/22/06 3:40 PM Page 8

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community). If I help you, I cannot so easily help create tensions within the group when individu- someone else, and I have to balance the loss that als’ preferred ecological, social or reproductive I accrue as a direct result against all my other gains. strategies differ. This becomes significant when individuals The importance of multi-level selection, espe- live in interdependent communities whose per- cially for understanding human behaviour, has sistence and success is a product of the effective- been stressed for many years by Wilson (1975; this ness with which individuals work together. In volume), but its implications have received very these cases, actions that destabilize the group’s little attention. It has acquired particular signifi- coherence—and the fragile social contract on cance in the light of the finding that human which its existence is premised—ultimately risk societies are themselves multi-level constructs. adversely influencing the fitness of the individ- Seen from the individual’s perspective, human ual decision-maker. Social (or even physical) social networks appear as a series of concentric ostracism inevitably has disastrous consequences circles (the so-called ‘circles of acquaintanceship’) for an individual, especially in small-scale soci- whose sizes have a surprisingly constant scaling eties. Cultural rules may provide particularly ratio of three (Zhou et al., 2005). Although there powerful mechanisms for enforcing social con- is considerable individual variation in the size of formity, not least by creating a sense of group these circles, nonetheless the typical sizes seem identity. From an evolutionary point of view, to be constant across a wide range of cultural and this may seem to result in individuals behaving socio-economic circumstances (from hunter- in ways that are sub-optimal when seen from gatherers to modern post-industrial societies). the individual’s purely selfish point of view. But Each circle corresponds not only to quite dis- a wider perspective may reveal that the individ- crete numbers of individuals, but also to particu- ual’s net lifetime fitness is higher if he/she lar frequencies of contact and feelings of intimacy accepts some losses now in the expectation of (Hill and Dunbar, 2003). We do not, as yet, under- receiving greater returns in the future. stand why human societies should have this The need to integrate culture into the story form (though it may well be a trait characteristic has been added extra impulse in recent years by of many mammals with complex social systems). two recent developments. One is the concept of Nonetheless, the different groupings seem to multi-level selection, and the other niche con- have social and ecological functions that are a struction theory. The principal issue behind critical component of our personal life-history both is that fitness may be influenced in a rather strategies. Since group-living is costly, we bene- complex way by the fact that an individual’s fit from living in communities of this kind only actions reverberate through the layers of the bio- if they work effectively. Hence, ensuring that the logical system. This has quite explicit implica- group functions as a coherent unit and is not tions in the case of niche construction theory, destabilized by individuals’ actions becomes an which argues that organisms can (and often do) essential component of our sociality. The tightly alter the environment they live in by their own integrated nature of human social groupings behaviour. Beavers and their dams are an obvi- means that each of us is deeply embedded in a ous and familiar example. But social groups complex network of relationships: as a result, themselves are a form of niche construction— the consequences of whatever we do inevitably indeed, they are perhaps the most complex form reverberates through the layers of the system of this phenomenon, especially when kinship is and has ramifications for everyone with whom part of the process. In effect, the social groups of we have to live. many monkeys and apes (and, by extension) The fact that societies exist as collaborative humans are implicit social contracts: individuals ventures itself raises an issue of considerable collaborate to solve the problems of everyday importance that has very much come to the fore survival and successful reproduction more effec- within the past few years in evolutionary studies tively than they can do on their own. Ensuring of human behaviour. This is the issue of social that the group functions effectively as a group cooperation. If we are to maintain—and thus has crucial feedback consequences for the fit- benefit from—socialities of this complexity, an ness of its individual members. It may also intense form of prosociality is necessary since 01-Dunbar-Chap01 12/22/06 3:40 PM Page 9

References · 9

group members must compromise on at least the current puzzles that bedevil the study of some of their self-interest. But any such social human behaviour may well evaporate when contract is always at risk of being destabilized by humans are seen as operating within a more freeriders (those who take the benefits of the complex multi-level social environment. social contract, but decline to pay all the costs). Social cooperation, and the behaviours that References derive from it (freeriding, altruistic punishment, second-order public goods problems) have Aiello, L. C. (1996) Terrestriality, bipedalism and the origin emerged as a particularly fruitful area of collab- of language. In W. G. Runciman, J. Maynard Smith and oration between evolutionary biologists, evolu- R. I. M. Dunbar (eds) Evolution of Social Behaviour Patterns in Primates and Man, pp. 269–290. Oxford tionary anthropologists and those who now University Press, Oxford. refer to themselves as evolutionary economists. Barrett, L., Dunbar, R. I. M. and Lycett, J. E. (2000) Though most often investigated in isolation, Human Evolutionary Psychology. Palgrave-Macmillan, these have to be seen within the broader picture Basingstoke and Princeton University Press, of both the evolution of multi-level social sys- Princeton, NJ. Cosmides, L. and Tooby, J. H. (1992) Cognitive adaptations tems and the role that culture plays in creating for social exchange. In J. H. Barkow, L. Cosmides and J. the environment within which cooperation H. Tooby (eds) The Adapted Mind, pp. 163–228. Oxford games are played out in real life. Some of the University Press, Oxford. chapters in Section VII will develop these Dunbar, R. I. M., Barrett, L. and Lycett, J. E. (2005) themes in more detail. An Introduction to Evolutionary Psychology. One World Books, Oxford. Forgas, J., von Hippel, W. and Haselton, M. (eds) (in press) Evolutionary Social Psychology. Psychology Press, New York. 1.4. Evolutionary psychology Hamilton, W. D. (1964) The genetical evolution of social behaviour. I, II. Journal of Theoretical Biology 7: 1–52. of the future Heyes, C. M. (2000) Evolutionary psychology in the round. In C. M. Heyes and L. Huber (eds) Evolution of We end this introductory chapter with two brief Cognition, pp. 3–22. Cambridge University Press, observations about the future. The first is that Cambridge. evolutionary psychology is now clearly here to Hill, R. A. and Dunbar, R. I. M. (2003) Social network size stay, notwithstanding the rather negative press in humans. Human Nature 14: 53–72. it has received in recent years. (We are reminded Plotkin, H. (2004) Evolutionary Thought in Psychology: somewhat wearily of the equally negative A Brief History. Blackwell, Oxford. Schaller, M., Simpson, J. and Kenrick, D. (eds) (2006) responses that greeted sociobiology in the later Evolution and Social Psychology. Psychology Press, 1970s: contemporary forecasts of its imminent— New York. indeed, actual—demise proved to premature.) Strassman, B. I. and Dunbar, R. I. M. (1998) Human However, its future, we are convinced, will depend evolution and disease: putting the Stone Age in on our capacity to integrate the various strands perspective. In S. C. Stearns (ed.) Evolution in Health and Disease, pp. 91–101. Oxford University Press, Oxford. that have developed over the past decade or so. Tinbergen, N. (1963) On the aims and methods of We hope this volume goes some way to initiat- ethology. Zeitschrift für Tierpsychologie 20: 410–433. ing that process. The second point is, we believe, Wilson, D. S. (1975) A theory of group selection. even more important, at least for the human end Proceedings of the National Academy of Sciences of the of evolutionary psychology. Embedding human USA 72: 143–146. Zhou, W-X., Sornette, D., Hill, R. A. and Dunbar, R. I. M. behaviour into the cultural matrix within which (2005) Discrete hierarchical organization of social humans live is, we believe, a particularly impor- group sizes. Proceedings of the Royal Society, London tant and crucial challenge. In our view, some of 272B: 439–444.