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Not by Genes Alone: How Culture Transformed Human Evolution

Richerson, Peter J. and Boyd, Robert
University of Chicago Press: Chicago, IL, 2005
ISBN 0226712842 (pb)

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Reviewed by Giangiacomo Bravo
Department of Social Sciences, University of Brescia and IRIS (Interdisciplinary Research Institute on Sustainability)

Cover of book One and a half century after Darwin's Origin of Species, evolution remains one of the big issues in science. Worse, if Stuart Kauffman (2000, 16) is right in his radical claim, 150 years after Darwin "we [still] do not understand evolution", at least in some of its more general properties. One (of the many) open question regards the "spectacular evolutionary anomaly" represented by our species, even in comparison with our close genetic relatives of the Pan genus. Richerson and Boyd answer to the question takes the form of a comprehensive theory of cultural evolution, based on Darwinian foundations and possibly able to uncover many of the mechanisms that link human biology with its unique ability to use cultural tools.

I understand that, from the point of view of JASSS readers, this book may represent a deception: despite the authors' modeler skills and despite the fact that most of their arguments are based on formal models presented in previous works (e.g. Boyd and Richerson 1989, 1992, 2002), it encompasses no formal model either in the math or in the computer simulation form. On the other hand, the authors' choice of limiting the formal analysis does not alter the deep rigor of their arguments, at the same time making the reading possible for a wider public, especially from the humanities. And that is the good news, since this work really represents a bridge between natural and social sciences, deriving the evolutionary tools from the former ones and applying them to one of the core problem of the latter: human culture in all its forms. The authors' aim (both meritorious and necessary) of filling the existing gap between the two realms of science is explicit. In their words, "the most fundamental questions of how humans came to be the kind of animal we are can only be answered by a theory in which culture has is proper role and in which it is intimately intertwined with other aspects of human biology" (p. 4, emphases in the original).

The two main arguments of the book make this point clearer. The first one, "culture is crucial for understanding human behavior" (treated mainly in chapters 1 and 3), is addressed explicitly to evolution, evolutionary psychology and sociobiology students. Genetic evolution and the gene-environment relationship cannot account by themselves for the huge amount of human behavioral variation empirically recorded. To include in the analysis socially acquired elements like beliefs or values, learnt from other peoples and transmitted from one generation to the next, is fundamental in order to understand the differences and the behavioral adaptability that characterizes our species. However, those elements vary not only from place to place, but also from time to time. In other words, culture evolves by following mechanisms that are in part similar but not identical to the genetic ones. Much like genetic evolution, people acquire behavior by teaching and imitation from their parents; unlike genetic evolution, non-parental teaching and imitation play also an important role while a number of "transmission biases" (e.g. "imitate the majority" or "imitate the successful") deeply influence cultural evolution processes.

The second main argument of the book, "culture is part of biology" (chapters 4 and 6), mainly addresses (vice-versa) to the wide group of social scientists who refute evolutionary explanations. Our evolved psychological mechanisms affect indeed our learning capabilities and even the way we think. On the other hand, since culture affects the survival and success of individuals and groups, it is part of human evolutionary process as much as the genes are. Genes and culture are probably strictly linked in a long co-evolutionary process that produced modern humans. This means that not only human psychology should have genetic bases that permit and support cultural evolution, but that the latter, once in place, contributed to modify the original environment in a way that influenced subsequent genetic change. Evidence of strong recent (< 40,000 years) selection on human phenotypes represents a first confirmation for this idea (Wang et al. 2006). If confirmed by other studies, gene-culture co-evolution would represent a key model for the explanation of some of the H. sapiens species peculiarities, including the unusual propensity of its members to cooperate in large groups of unrelated individuals.

The cultural evolution framework illustrated by Boyd and Richerson is, by admission of the authors themselves, little more than a first tentative to build a synthetic theory of human behavior. As it happens with any good theory, it raises more questions than answers. Moreover, the way toward a better integration between natural and social sciences (and within the social sciences themselves) is difficult, but worth following. I hence recommend scholars having both natural and social science backgrounds and interested in social simulation to read the book and to try to incorporate some of its ideas in their models. Hopefully, good science will follow.

* References

BOYD R and RICHERSON PJ (1989) The Evolution of Indirect Reciprocity. In Social Networks, 11: 213-236.

BOYD R and RICHERSON PJ (1992) Punishment Allows the Evolution of Cooperation (or Anything Else) in Sizable Groups. In Ethology and Sociobiology, 13: 171-195.

BOYD R and RICHERSON PJ (2002) Group Beneficial Norms Can Spread Rapidly in a Structured Population. In Journal of Theoretical Biology, 215: 287-296.

KAUFFMAN SA (2000) Investigations. Oxford: Oxford University Press.

WANG ET, KODAMA G, BALDI P, and MOYZIS RK (2006) Global Landscape of Recent Inferred Darwinian Selection for Homo sapiens. In Proceedings of the National Academy of Sciences USA, 103: 135-140.


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