Cultural and Genetic Inheritance in the Constitution of Human Society

Home , Coevolution, Cultural evolution, Dual inheritance theory

Review of Robert A. Paul Mixed Messages: Cultural and Genetic Inheritance in the Constitution of Human Society

Herbert Gintis

December 12, 2016

Robert A. Paul’s recent book is an extremely broad-ranging and informative in- vestigation of cultural dynamics in small-scale societies. Paul is a cultural anthro- pologist with a broad range of sociological knowledge concerning such societies. His theoretical framework is that of dual inheritance theory, which he applies it to a vast number of issues in different societies. His analysis is very successful scientifically and yet remains enjoyable throughout. He is an excellent writer and the book fits together well. Dual inheritance theory, as I explain below, arose as a theory of the interaction between genes and culture in the evolutionof our species—the only known species to which the notion of long-term cultural evolution applies. Paul’s interpretation of this theory is, however, purely cultural. This interpretation is idiosyncratic, but defensible because he is dealing with societies in time periods too short for extensive genetic evolution to have taken place. Paul’s version of dual inheritance theory posits that there are two compet- ing/conflicting systems of human sociality. The first is kinship/family, which we share with innumerable other species. The second is “tribal,” which does not sup- press family, but promotes cooperation, amity, and regard independent of kinship genealogy. He suggests that human cultural symbolic systems induce individuals to stress their cooperation and friendship with non-family, which accounts for our success as a species. Paul has thought deeply about thesematters, and his treatment is well worth thinking about. The reason this interpretation of dual inheritance theory is plausible is that humans share with innumerable sexually-reproducing species the tendency to favor family members over genealogically distant individuals. It follows that kin/family preference is genetic in a way that tribal preferences

1 are not (applying, as they do, only to our species). Paul stresses repeatedly that kinship/family and tribal cultural systems develop almost independently, and are often in conflict. The fitness-reducing nature of some cultural institutionswas stressed by Robert B. Edgertondecades ago in his in his Sick Societies: Challenging the Myth of Primitive Harmony (New York, Press, 1992), and curiously Paul does not reference this great book at all. I suspect that Paul prefers the term “dual inheritance” to “gene-culture coevolution” because the latter suggests harmony, not conflict, between the two systems. Paul’s treatment of human evolutionary theory is, however, not completely bal- anced. First, he refers to the masters of inclusive fitness theory only in the his- torical section of the book, and he misstates repeated the notion that individuals can spread their genes only by personal biological reproduction. This is not a big problem, but it is incorrect and very annoying. Moreover, it conflicts with one of Paul’s major building blocks, the kinship/familynexus. As was shown long ago by William—see, for instance, his collection of articles Narrow Roads of Gene Land, Oxford University Press, 1998—individuals can enhance their fitness both by rais- ing more offspring or by helping relatives to raise their offspring, precisely because relatives share more genes that randomly selected groups of individuals. Indeed, the main reason humans differentially help relatives is not that we share genes for kin-helpingwith other species, but because Hamilton’snotion of “inclusivefitness” appliesjust as much to humans as to other species. Genes that promote cooperation independent of kinship,the key to our success as a species, can also spread, accord- ing to standard population biology—see, for instance my recent book with Samuel Bowles, A Cooperative Species: Human Reciprocity and its Evolution (Princeton: Princeton University Press, 2011). But the mechanisms are rather subtle and apply only to highly social species, as has been stressed by Bert Holldobler and Edward O. Wilson—see their inspiring work The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies (New York: Norton, 2008). A second imbalance in his treatment is that he makes no case whatever for the gene-side of dual inheritance theory, or what I prefer to call gene-culture coevolution, a process which is of fundamentally important interest in making humans what they are, independent from the clash of kinship/family versus tribal values. Gene-culture coevolution explores the evolutionary dynamic that applies to any species for which epigenetic information takes the form of culture that accumu- lates reliably and long-term across generations. That applies stronglyonly to Homo sapiens. The main point is that culture includes techniques and social norms that determine which genes will be evolutionarily rewarded in a given society. There- fore human genes are the product of human culture as much as the reverse. This theory was developed by Lumsden and Wilson (1981), Cavalli-Sforza and Feld- man (1981), and Boyd and Richerson (1985), and has become a major branch of

2 evolutionary theory. Indeed, it is supplies the basic framework of my recent book Individuality and Entanglement: The Moral and Material Bases of Human Social Life, Princeton University Press, 2016. I give, as an extended example of the intimate links between genes and culture in humans, the evolution of the physiology of communication. This example is important because it involves the development of key human genetic capacities that are the product of social structure as opposed to simple individual adaptation. The physiology of communication in humans is an emergent property of human social evolution (Gintis 2011). The example is especially relevant to this journal, which explores the evolutionary roots of the humanities. How are genes and human culture similar? Both genes and human culture con- sist of information passed across generations and subject to mutation and selection. How have humans managed to evolve their extraordinary capacity for verbal com- mumnication? Persuasive and informative speakers in the hunter-gatherer period of our existence were rewarded with higher quality mates and increased reproduc- tive opportunities. Their offspring inherited their cognitive and physiological com- municative powers. This is gene-culture coevolution of human communication, operating over tens and hundreds of thousands of years. The evolution of the physiology of speech and facial communication presents a theoretical challenge. It is easy to explain, if everyone else is gabbing away and you can only grunt and pant, why you might be handicapped in finding a spouse and teaching your children. But how could the use of complex phonics begin? When everyone is grunting and panting, what is the fitness benefit of being able to make more complex varieties of sounds? What is the fitness benefit of being able to interpret complex sounds? The answers are far from obvious and go far beyond simple individual fitness, or even inclusive fitness, maximization. For this reason, the evolution of the physiology of speech is a dramatically complex example of gene-culture coevolution. A most common error in the litera- ture is to consider language as a purely mental phenomenon that can be explained simply as a byproduct of brain size and intelligence. In fact, the ability to com- municate through facial sign and speech has required major changes in human physiology. These could only have come about because individuals with superior communication capacities were rewarded with more and healthier children. Why might this have occurred? The increased social importance of communication in human society rewarded genetic changes that facilitate speech. Regions in the motor cortex expanded in early humans to facilitate speech production. Concurrently, nerves and muscles to the mouth, larynx, and tongue became more numerous to handle the complexities of speech (Jurmain, Nelson, Kilgore and Travathan 1997). Parts of the cerebral cortex, Broca’s and Wernicke’s areas, which do not exist or are relatively small

3 in other primates, are large in humans and permit grammatical speech and com- prehension (Binder, Frost, Hammeke, Cox, Rao and Prieto 1997, Belin, Zatorre, Lafaille, Ahad and Pike 2000). Adult modern humans have a larynx low in the throat, a position that allows the throat to serve as a resonating chamber capable of a great number of sounds (Relethford 2007). The first hominids that have skeletal structures supporting this laryngeal placement are the Homo heidelbergensis, who lived from 800,000 to 100,000 years ago. In addition, the production of consonants requires a short oral cavity, whereas our nearest primate relatives have much too long an oral cavity for this purpose. The position of the hyoid bone, which is a point of attachment for a tongue muscle, developed in Homo sapiens in a manner permitting highly precise and flexible tongue movements. Another indication that the tongue has evolved hominids to facilitate speech is the size of the hypoglossal canal, an aperture that permits the hypoglossal nerve to reach the tongue muscles. This aperture is much larger in Neanderthals and humans than in early hominids and nonhuman primates (Dunbar 2005). Human facial nerves and musculature have also evolved to facilitate communication. This musculature is present in all vertebrates, but except in mammals it serves feeding and respiratory functions alone (Burrows 2008). In mammals, this mimetic musculature attaches to the skin of the face, thus permitting the facial communication of such emotions as fear, surprise, disgust, and anger. In most mammals, however, a few wide sheetlike muscles are involved, rendering fine information differentiation impossible, whereas in primates, this musculature divides into many independent muscles with distinct points of attachment to the epidermis, thus permitting higher bandwidth facial communication. Humans have the most highly developed facial musculature by far of any primate species, with a degree of involvement of lips and eyes that is not present in any other species. In short, humans have evolved a highly specialized and very costly complex of physiological characteristics that both presuppose and facilitate sophisticated aural and visual communication, whereas communication in other primates, lacking as they are in cumulative culture, goes little beyond simple calling and gesturing capacities. This example is quite a dramatic and concrete illustration of the intimate interaction of genes and culture in the evolution of our species.

REFERENCES

Belin, P., R. J. Zatorre, P. Lafaille, P. Ahad, and B. Pike, “Voice-selective Areas in Human Auditory Cortex,” Nature 403 (2000):309–312. Binder, J. R., J. A. Frost, T. A. Hammeke, R. W. Cox, S. M. Rao, and T. Prieto,

4 “Human Brain Language Areas Identiﬁed by Functional Magnetic Resonance Imaging,” Journal of Neuroscience 17 (1997):353–362. Boyd, Robert and Peter J. Richerson, Culture and the Evolutionary Process (Chicago: University of Chicago Press, 1985). Burrows, Anne M., “The Facial Expression Musculature in Primates and Its Evo- lutionary Signiﬁcance,” BioEssays 30,3 (2008):212–225. Cavalli-Sforza, Luigi Luca and Marcus W. Feldman, Cultural Transmission and Evolution (Princeton: Princeton University Press, 1981). Dunbar, Robin M., The Human Story (New York: Faber & Faber, 2005). Gintis, Herbert, “Gene-culture Coevolution and the Nature of Human Sociality,” Proceedings of the Royal Society B 366 (2011):878–888. Jurmain, Robert, Harry Nelson, Lynn Kilgore, and Wenda Travathan, Introduction to Physical Anthropology (Cincinnati: Wadsworth Publishing Company, 1997). Lumsden, Charles J. and Edward O. Wilson, Genes, Mind, and Culture: The Co- evolutionary Process (Cambridge, MA: Harvard University Press, 1981). Relethford, John H., The Human Species: An Introduction to Biological Anthro- pology (New York: McGraw-Hill, 2007).

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