I agree with Stoneking that the case of lactose tolerance reveals something very interesting. There culture modifies the standing resources of the environment in a way to benefit those that can take advantage of it. And much of the rest of the phenomena he is referring to may represent population encounters with other foods, as well as toxins and diseases. These resources and hazards are plausible suggestions because they perdure, enabling them to drive selection over many generations.

These resources and hazards are what we might think of as “basic level” in that a sustained encounter with them will generate selective pressure, and culture can play a role in altering the probability of the sustained encounter. A different sort of resource is more thoroughly cultural: for example having a good job or a large amount of money with which one can purchase goods. These latter “symbolic” resources are beneficial only insofar as there is a society that will convert them into more basic level goods.

I mention this distinction between basic level and symbolic level goods and hazards because an intriguing question in the context of culture-driven selection (though much further along towards simple conjecture than anything Stoneking suggests) is to what extent ongoing selection is driven, in part, by access to symbolic as opposed to basic level goods and hazards.

Cochran, Hardy, and Harpending (2006) have offered the surprising argument that cultural practices of ethnic/racial classification and professional discrimination against Jews in the 9th to the 17th century in Eastern Europe created selective pressure for higher IQs among Ashkenazi Jews but also certain genetic diseases (e.g. Tay-Sachs) that are linked to high IQ. Specifically, they hypothesize that discrimination limited the available employment for Jews to certain professions that themselves required high IQs. In effect, the authors argue that culture altered the environment – altered the symbolic resources – of an entire human subpopulation that was largely reproductively isolated for a sustained period in ways that drove selection. I don’t know if this specific claim is right, but it does point to questions for cultural selection that promise to expand its scope. Questions like: has symbolic culture remained stable enough over long periods of time to represent a selective force? If so, where and when? The circumstances of cultural stability surrounding Cochran et al.’s case are such that they will not ubiquitously generalize. But they do lead us to consider what range of cultural circumstances might be relevantly similar.

My own guess (and it is just a guess) is that culture-driven selection can only generalize so far. This is because human symbolic culture is, famously, highly variable in a way that makes any evolutionary problems it poses into moving targets for the slow work of natural selection. Indeed, (and this is quite conjectural) it seems that in the last few millennia cultural change has been remarkably rapid. If that is right, the situation that Cochran et al. make reference to may be anomalously stable.

Here is another conjecture: where there is culture-driven selection, we might expect that the cultural elements in question are themselves stabilized by standing psychological biases of the sort suggested in recent evolutionary psychology and anthropology – for example, biases to think about human groups in an essentialized way (e.g. Hirschfeld 1996, Gil-White 2001; Machery and Faucher 2005). Where these biases are present are operating they may stabilize culture allowing culture to drive selection over a sustained period.

Where culture is more variable, however, the moral looks to be that when we talk about culture driving evolution, symbolic resources like good jobs probably do not play as large role in ongoing human evolution as compared to ongoing encounters with new basic level resources and hazards like food, toxins and disease.

References:

Cochran, G., J. Hardy, et al. (2006). “Natural History of Ashkenazi Intelligence.” Journal of Biosocial Science 38: 659–693.

Gil-White, F. (2001). “Are Ethnic Groups Biological ‘Species’ to the Human Brain?” Current Anthropology 42(4): 515-554.

Hirschfeld, L. A. (1996). Race in the Making: Cognition, Culture, and the Child’s Construction of Human Kinds. Cambridge, MA, MIT Press.

Machery, E. and L. Faucher (2005). “Social Construction and the Concept of Race.” Philosophy of Science 72: 1208–1219.

First, Stoneking’s opposition of the notions that culture prevents selection on genes and that culture drives selection on genes is of course the classic one. That many nonspecialists continue to think in this way is a continued puzzle to the specialist commentators here. On top of their specific comments, I want to make clear that a basic reason to refuse to frame the discussion in the binary opposition (culture does or does not cause selection) is because culture does both things—it both prevents selection on genes and allows novel selection on genes.

The argument that cultural adaptation—the ability of individuals and groups to socially evolve and transmit behavioral strategies that are adapted to local contexts—reduces selection on genetic variation has a lot going for it. The peoples of the arctic have not had to re-evolve fur, because clothing and the control of fire substitute in maintaining body temperature. If the existing genetic variants in the population are sufficiently close to the phenotypic optimum, then culture and other forms of behavioral adaptation can make these genetic variants essentially invisible to selection. “Sufficiently close” in this context must refer to how far socially transmitted behavior and technology can move phenotypes. In the case of clothing, socially transmitted traditions can produce tremendous insulation, meaning that genes for producing modest amounts of body hair can be nearly or just as successful as genes producing more body hair.

The opposite argument, that culture actually produces new selection pressures, arises from the same logic. When the existing genetic variants in the population are all very far from the phenotypic optimum, it is only via socially transmitted behavior that people can expose these variants to natural selection. As hominins expanded their range out of Africa, the many novel environments they encountered would have selected for new genes. But in many cases, it is likely that the existing genetic variants were all very poorly suited to a new ecology, and as a result, none were favored over others by the action of natural selection. It’s like asking which contemporary human genetic variants would have highest fitness in an aquatic environment—since we would all drown, and there are no genes for having gills, selection can’t make progress yet. Cultural adaptations, however, would have allowed populations to essentially shift all of these variants towards being more optimal. Then some of them would possibly have higher fitness and increase in frequency, allowing for selection to get leverage where previously there was little. Consider again the evolution of aquatic adaptations—if we begin with SCUBA gear and underwater domes, genetic variants for respiratory efficiency suddenly become relevant where none before would have allowed even survival.

The thought experiments above are silly in many ways. But they are chosen to illustrate the logic of how cultural dynamics both make selection weaker and stronger, depending upon how from the phenotypic optimum existing genetic variants lay. So while cultural evolution is special in many ways, it’s also just another example of genetic systems creating developmental processes that alter how selection acts on the genome. The argument I just made for culture has been made by scholars of evolutionary development for other mechanisms, notably systems for growth and the regulation of organismal development. Developmental systems are not blueprints for what an organism will look like at maturity. Instead they are highly dynamic recipes and “learn” in meaningful ways. They can adjust phenotypes and therefore accommodate genetic variants that are close to the optimum. And when no genetic variants would survive otherwise, they can shift the phenotype close enough to expose the existing variation to selection (see Gerhart and Kirschner cited at at the end for a fuller discussion of these mechanisms and pointers to the broader literature).

These two processes—the weakening and strengthening of selection via culture—must interact over evolutionary time. When genetic variation is accommodated by cultural “silencing,” this allows selection to be more efficient when the context changes (perhaps due to culture itself) and these variants become useful. The maintenance of genetic variation is a resource for populations, and so even when culture is reducing natural selection on short time scales, it may be cultivating our futures.

Now my second point: There is a strong thesis lurking in this topic that human nature is in fact socially constructed. If people believe something, even if false, those beliefs can reconstruct the facts, over social and evolutionary time scales. This means it shouldn’t be possible to make a complete account of human biology without accounting for socially constructed beliefs, because beliefs exert tremendous effects on the fates of genes. If most North Americans believe in the category “black” and treat “blacks” differently, then this will have tremendous material effects on “blacks,” even though the biological nature of this category is famously specious. Various versions of this kind of hypothesis have been explored recently, most notably Philip Kitcher’s (1999) speculation about the possible social construction of real genetic differences and Cochran et al’s (2006) argument that social identity processes lead Ashkenazi Jews to be selected for particular mental traits, that their intelligence is really socially constructed. Whatever one makes of these particular cases, the possibility is great that the demography and behavior of human populations is always interacting with socially constructed categories like “gender” and “race” and “IQ.” The most cogent discussion of this particular possibility that I know is by Mallon (2008).

The influence of culture is so thorough that human nature can only be understood as culturally evolved. One can no more label some portion of human nature “cultural” than one can say some portion of a sexual species is “sexual.” Sexual reproduction changes how evolution proceeds, such that accounting for evolutionary change in sexual species is different than in a-sexual ones. Likewise, a highly cultural species like ourselves is fully cultural as well as fully biological. We socially construct our natures and thereby continually remake our images of ourselves, as well as our genomes.

References

Cochran, G., J. Hardy, et al. (2006). “Natural History of Ashkenazi Intelligence.” Journal of Biosocial Science 38: 659–693.

Gerhart, J. and M. Kirschner. (2007). The theory of facilitated variation. PNAS 104(S1):8582-8589.

Kirschner, M. and J. Gerhart. (1998). Evolvability. PNAS 95(15):8420-8427.

Kitcher, P. (1999). “Race, Ethnicity, Biology, Culture”. In Racism. ed. L. Harris. New York, Humanity Books: 87–120.

Mallon, Ron, “Naturalistic Approaches to Social Construction”, The Stanford Encyclopedia of Philosophy (Winter 2008 Edition), Edward N. Zalta (ed.), URL = .

Being clear about what we mean by evolution is important, and Stoneking rightfully notes this. When considering selection at the genetic level, individual death and quality of life do not matter as long as the genetic material in question is passed to subsequent generations at a sustainable frequency. But the idea that if “culture is unable (or unwilling) to do what it takes to prevent or cure a disease, then genetic resistance will indeed occur and will increase in frequency” is an oversimplification. Such responses to selection pressure at the genetic level assume that the appropriate underlying genetic variation exists and that fitness is significantly curtailed. However, if drugs can keep people with AIDS alive for long periods they can achieve a degree of reproductive success and there may be nothing for selection to respond to. Or, people may be dying of the disease in their 20s and 30s without any drug intervention but still reproducing (reducing selection pressure). There also might be a wide array of behavioral, ecological, physiological, and developmental variants that affect the rates, virulence, density and patterns of HIV across and within populations. Understanding human evolution involves much more than focusing on just natural selection and/or “culture”.

I agree that culture should not be seen merely as a “buffer” and that cultural activity can affect selection pressures, but that is only a small part of the story. We need to also include recent contributions in evolutionary theory that complexify basic selection scenarios and examine the roles of behavioral, epigenetic, and symbolic inheritance (Jablonka and Lamb, 2005), and niche construction and ecological inheritance (Odling-Smee et al. 2003). To envision human evolution basically as natural selection and culture affecting change is too limited a view of evolutionary processes (Fuentes 2009).

Fuentes, A. (2009) Re-situating Anthropological approaches to the evolution of human behavior. Anthropology Today 25(3):12-17
Jablonka, Eva and Lamb, Marion (2005)Evolution in four Dimensions: genetic, epigenetic, behavioral, and symbolic variation in the history of life Cambridge, MA: MIT Press
Odling-Smee, F. J., Laland, K.N., and Feldman, M.W. (2003) Niche construction: The neglected process in evolution Monographs in Population Biology 37. Princeton University Press, Princeton

Natural and sexual selection are well known in small populations. Those individuals best adapted to the local environment or that have traits favoured by potential mating partners are favoured. In larger populations, provisioning can occur for traits that do not map directly on to sexual selection or fitness for survival in the current environment.

Any human individual can contribute to this provisioning by endorsing favoured traits recognised in individuals or groups of individuals. Consuming music, artwork and other creative output an individual may display, voting for favoured politicians or vocally supporting a position held by a particular individual all contribute to that favoured individual’s eventual fitness either directly or via the prominence of the favoured trait.

This may not be immediately obvious when the artist, for instance, is homosexual or otherwise not contributing to the gene pool of the next generation. But let us consider a gene-centric view of this common cultural dynamic. Let us consider an imaginary gene that confers an abstract reward for the appreciation of symbolic representation eg art work, language and literature appreciation and so on.

If those who express the gene in a culturally salient manner are rewarded, then those who have the gene will also be strongly attracted to expressing that gene through culturally salient manner (you can not create good art unless you can appreciate art) and those that do, even weakly, will have a sexual selection advantage over those that do not. Even though an individual who has the gene but does not express it culturally (by doing art) nor has offspring (that would perpetuate the gene), the frequency of the gene can increase in subsequent generations if this individual favours those who also have the gene eg by buying their artwork, by teaching art to students, by donating resources to art institutions or by hailing the achievements of artists.

This dynamic has a salient manifestation at all levels from tribal groups through to modern times and represents a mechanism for influencing gene frequency outside of direct reproduction (you can influence the frequency of gene expression that produces a trait valued by you without having children).

Only human culture has the capacity to mediate this extra-sexual modulation of gene frequency, and the biggest influence on evolution that human culture has had is the consolidation of this extra-sexual form of evolution. No such extra-sexual modulation of gene frequency is seen in the culture of any other species (eg chimpanzee).

Posted by
Robert Karl Stonjek

The interaction between cultural evolution (change in beliefs, norms, behaviors, etc.) and biological evolution (change in phenotype due to genetic changes—whether these are due to selection or drift) is bound to take many forms, just like niche construction. As is well illustrated in numerous species, niche construction sometimes buffers organisms from changes in their environment and, as a result, from new selective pressures—a point noted by Stoneking in his thought-provoking essay. But, by modifying the environment in which organisms live, niche construction also creates new selective pressures, resulting in the biological evolution of the relevant populations—a point also made by Stoneking. Similarly, culture is bound to have worked as a buffer during human evolution, while also creating new selective pressures. Both effects of culture (culture as a buffer and culture as an engine) should be kept in mind when one speculates about the importance of culture for the evolution of the human mind.

Hypotheses about the role of culture on human evolution in general, and on the evolution of the human mind in particular, abound in the human evolutionary behavioral sciences. As Boyd and Richerson have noted, one can identify across cultures, epochs, and social systems a particular form of social organization (involving several thousands members who share some distinctive social norms as well as some markers identifying their group membership), and here culture has plausibly been working as a buffer, preventing the emergence of new selective pressures that would have modified fundamental aspects of our social cognition. On the other hand, following others, I have hypothesized that culture allowed for the development of large social groups, which itself resulted in the selection of a distinctive form of social cognition (Boyd and Richerson; Gil-White; Machery and Faucher). Here culture was the engine of biological evolution.

Thus, hypotheses about the role of culture as a buffer or as an engine in the evolution of our species abound. Some are reasonably supported, while others are frankly speculative. However, one should honestly acknowledge that there are few uncontroversial examples. In this respect, it is stunning to see Stoneking give the example of lactose tolerance! Not because this is a controversial example: In fact, it is a well-established example of culture causing biological evolution (e.g., Tishkoff et al.). But because this example has been discussed for at least three decades, and by now I wished we had other well-supported examples!

But still, despite the scarcity of uncontroversial examples, I do not doubt for a minute that culture has played a major role in human evolution, particularly in the evolution of the human mind.

But it should also be acknowledged that when people say that cultural evolution has replaced biological evolution, they often have a distinct thought in mind—i.e., they typically do not mean to deny that the advent of a distinctive form of information transmission has had a major influence on the biological evolution of humans. Rather, they want to highlight the fact that for at least a few millenaries the dramatic behavioral changes in our species have very little to do with biological evolution (if anything at all).

In addition, culture might have a weaker and weaker influence on the biological evolution of human behavior and mind. It is plausible that cultural changes are taking place at an increasing rate, and this for several distinct reasons. Among others: a large segment of our societies is dedicated to invent new ideas, norms, fads, practices, etc., while another segment of our societies is dedicated to transmit these ideas, norms, etc., to others; the strength of social norms seems weaker in large, modern societies than in smaller societies, which allows for faster, more common changes. As a result, it might be that the rate of cultural evolution is too fast for biological evolution to catch up, since biological evolution is bound to be slower than cultural evolution. If this is true, then culture might have stopped creating new selective pressures on human behavior mind!

And this presents a problem because speciation is slow and rare in multicelled animals. So most of the time speciation is not occurring, just a few variations on a phenotypic theme that may be quickly reversed if the local conditions changed, as Darwin discovered when he observed pigeon varieties reverting to the wild type in just a few generations when human mediated selection was removed.

But in any population in a relatively stable environment we can observe exactly what evolution is up to. Variation begins to accumulate in the population, in the genome if there is little or no sexual selection and in the phenome if there is strident sexual selection and the population is robust enough to tolerate less than optimal variations.

If we imagine that instead of evolution itself evolving it was a planned mechanism then we might proffer that this strategy trades optimal performance in the current environment for maximal future proofing of the population ie there is a phenotypic variation for every conceivable environmental variation that may occur. Populations may retain variations that were successful in the past, but there is no way for a population to anticipate the future. Thus all variations that can be supported are retained.

Few species have had the luxury to retain variations both in genomic and phenomic forms. Finches in the Galapagos island appear to be able to draw on stored variations within a generation or two if the food source changes and a different beak shape is required.

But humans are enormously successful and can retain variation both in the genome and phenome, and this form of evolution is robustly evident today.

In the past few centuries there has been a rapid adaptation to global conditions with those individuals not able to withstand ‘common diseases’ being wiped out.

Lactose tolerance can not, however, be considered an evolved ‘human’ trait as lactose tolerance is not a species wide trait:
“The frequency of decreased lactase activity ranges from as little as 5% in northern Europe, up to 71% for Sicily, to more than 90% in some African and Asian countries” [from a Wikipedia entitled ‘Lactose Intolerance’, referencing “Correlation between lactose absorption and the C/T-13910 and G/A-22018 mutations of the lactase-phlorizin hydrolase (LCT) gene in adult-type hypolactasia”
]

Culture in humans has too many functions for any generalisations to be made. One must at least state whether the informational content of culture is being considered, the artefacts of culture (tools and fire through to cities and industry), the prescriptive behaviour modulators (laws and law makers including governments, religious moral codes etc) or the human imperative (eg currently, humans think of themselves as a species with the right to choose to dominate and utilise or protect any other species). Would information alone be sufficient for a human population to rebuild? (if so, what would stop a slightly more advanced chimp or computer from claiming the rights and privileges of ‘a human’?)

Several years ago, in the course of researching a book on music, I read a book review in Science that recommended Russell A. Barkley’s review and synthesis of the ADHD literature, ADHD and the Nature of Self-Control. Barkley argued that ADHD does not involve inattention as much it involves poor self-control, which Barkley argues is a failure of some central executive function. In turn, Barkley asserts that the “nature of this central executive . . . is time. More specifically, it is the conjecturing of the future that arises out of reconstruction of the past and the goal-directed behaviors that are predicated on these activities. Such activities . . . permit self-regulation relative to time” (p. 202).

Barkley went on to point out that “time is an integral, inseparable part of the physical world” (p. 204), that “our will, therefore is . . . at time’s beck and call” (p. 205) and thus that “time, timing, and timeliness . . . become important concepts in understanding . . . goal-directed behavior and in determining it” (p. 209).

Musical performances are, of course, exquisitely timed. One of the major theories about our response to music specifically focuses on the way it plays with our expectations, sometimes satisfying them, sometimes not (Meyer 1956). Beyond that, the brain itself necessarily operates in time; its activities must be well-timed or they will fail. Thus, it seemed to me that music might be an activity that the brain uses to adjust and train its own timing so that expectation (of future sounds) and fulfillment (through motor execution of the musical sounds) are properly matched.

So, when I completed the book (Benzon 2001) I decided to explore possible connections between ADHD in music. I had argued, on the one hand, that music-making is fundamental to human psychobiology. However, over that last century or so music-making has diminished in advanced industrial societies because of the ready availability of recordings. Has that had a deleterious effect on us, the members of such societies? Is the rise of ADHD, in part, an effect of the diminished presence of active music-making in our lives?

I can’t say I found strong evidence on the question one way or another, though I have written up some informal notes in the form of a working paper (Benzon 2009). The ADHD literature is large, contentious, and, at the time (roughly late 2002), not terribly conclusive: something’s going on, but just what is rather obscure. While there is some anecdotal evidence about the efficacy of music therapy in ameliorating the effects of ADHD, very little attention has been given to the possible relationship between music-making and ADHD, and that despite the fact that one of the leading ADHD researchers, Barkley, sees timing problems at the heart of ADHD.

For what it’s worth, here’s a summary of what I found out about the genetics of ADHD. Bear in mind that I did this review seven years ago and haven’t looked at the literature since then. There is some evidence of some kind of cultural linkage, but just what that is, that’s not clear.

Barkley reviewed a number of studies involving families, adopted children, and twins indicating that there is a hereditary component to ADHD (pp. 37-40). There is no evidence that ADHD is caused by chromosomal abnormalities (p. 37), but it is clear that a variety of genes predispose an individual for ADHD. We do not yet have any clear picture of these genetic factors (Comings et al. 2000).

Much of the genetic work centers on various dopamine genes. Barkley reports that initial work focused on the gene for the D2 dopamine receptor, but that there has been trouble replicating that work (cf. Todd and Lobos 2002). More recent work has focused on the dopamine transporter gene and a particular allele of the gene for the D4 dopamine receptor (DRD4). The dopamine transporter clears dopamine from the intercellular space once it has been secreted; thus a deficiency in the transporter would result in abnormally high levels of dopamine in the synaptic space. A recent article (Schmidt et al. 2001) on DRD4 concludes that variation in its alleles accounts for 5-7% of the variance in reported attention problems in a sample of children (primarily white and middle-class) that has been followed for seven years. That is to say, the gene certainly has some effect on attention, but we cannot claim to have found the key that opens the door on this particular mystery. Another study found DRD4-associated attention problems in 1 year olds (Auerbach et al. 2001).

More recently Ding et al. (2002) reported on the world-wide distribution of the different alleles of the D4 dopamine receptor gene. They suggest that a particular allele (known as 7R) “originated as a rare mutational event that nevertheless increased to high frequency in human populations by positive selection” (p. 309). That is to say, once this allele appeared, it spread through the population because it contributed to the fitness of individuals having it. They further suggest that cultural differences might be involved, though they don’t suggest what those differences might be. With respect to disorders such as autism and ADHD they “suggest entertaining the possibility that predisposing alleles in fact are under positive selection and only result in deleterious effects when combined with other environmental/genetic factors” (p. 314).

In an accompanying commentary, Harpending and Cochran (2002) discuss two hypotheses about the possible cultural influence. One suggestion is that 7R is a “dispersal morph,” increasing “the likelihood that its bearers migrate.” Their own hypothesis, however, is that “7R bearers enjoy a reproductive advantage in male-competitive societies, either in competition for food as children or in face-to-face and local group male competition. Societies in which this advantage would be present were rare before the spread of agriculture, but common after it.”

I have no comment to make about either of these hypotheses.

References:

Auerbach, J. G., J. Benjamin, et al. (2001). “DRD4 related to infant attention and information processing: a developmental link to ADHD?” Psychiatric Genetics 11: 31-35.

Barkley, R. A. (1997). ADHD and the Nature of Self Control. New York, The Guilford Press.

Benzon, W. L. (2001). Beethoven’s Anvil: Music in Mind and Culture. New York, Basic Books.

Benzon, W. L. (2009). Music and the Prevention and Amelioration of ADHD: A Theoretical Perspective. Available at SSRN: http://ssrn.com/abstract=1527090

Comings, D. E., R. Gade-Andavolu, et al. (2000). “Multivariate analysis of associations of 42 genes in ADHD, ODD and conduct disorder.” Clin Genet 58(1): 31-40.

Ding, Y.-C., H.-C. Chi, et al. (2002). “Evidence of positive selection acting at the human dopamine receptor D4 gene locus.” PNAS 99(1): 309-314.

Harpending, H. and G. Cochran (2002). “In our genes.” Proceedings of the National Academy of Sciences 99(1): 10-12.

Meyer, L. B. (1956). Emotion and Meaning in Music. Chicago, University of Chicago Press.

Schmidt, L. A., N. A. Fox, et al. (2001). “Association of DRD4 with attention problems in normal childhood development.” Psychiatric Genetics 11: 25-29.

Todd, R. D. and E. A. Lobos (2002). “Mutation screening of the dopamine D2 receptor gene in attention-deficit hyperactivity disorder subtypes: Preliminary report of a research strategy.” Am J Med Genet 114(1): 34-41.

In what way has culture influenced genetic evolution of human beings? It is an illuminating perspective that Stoneking develops. It opens doors to new insights and raises questions about received wisdom. Or does it?

First, it is useful to clarify that culture is not the constant factor Stoneking’s description suggests. Culture evolves. The interesting question is therefore how cultural evolution influences genetic evolution of human beings. This perspective is well established in the literature on “dual inheritance” or gene-culture coevolution (Boyd and Richerson 1985, Durham 1991). Durham (1991) has a beautiful account of the lactose tolerance example where he shows how cultural instructions in a population directly influence the differential reproduction of genes and genotypes. In his example culture evolves in a separate inheritance track.

Cultural evolution can be described in the following way (Hodgson and Knudsen, forthcoming). From a prior state of instinct-driven behavior, habits made it possible to form and transmit dispositions to engage in useful behaviors in response to particular situations. The evolution of habits facilitated the coding and transmission of experiential learning relating to essential tasks such as hunting and farming. The medium was learning by imitation in human populations and the advantage was that it became possible to change behavioral repertoires on time-scales much shorter than those accounting for the genetic evolution of instincts. Cultural evolution involves a replication-machinery where we spread our habits of action and thought rather than our genes. So far so good.

But social evolution has led to much greater complexity than is usually considered in the literature on gene-culture coevolution. There are many important features of this story. Among these are a number of major transitions in the way information (above the genetic level) is transmitted, stored and utilized. Examples include the emergence of language, custom, law, and institutionalized science and technology.

Social evolution includes the evolution of culture. The potential for complexity in social evolution has greatly increased. But it is unclear in what ways social evolution has influenced the potential for complexity of genetic (human) evolution. In part, the answer to this problem depends on the relevant time-scales for the evolutionary dynamics. It is commonly understood that social (and cultural) evolution occurs at much short time-scales than genetic evolution. Are there good reasons to revise received wisdom in that regard? Or does social evolution primarily influence the developmental potential of genes associated with phenotypic plasticity, e.g. a potential to increase life-span because of improved food-preparation and nutrition? These are exciting problems, and Stoneking should be commended for triggering our thoughts about them.

References

Boyd, Robert and Richerson, Peter J. (1985) Culture and the Evolutionary Process (Chicago: University of Chicago Press).

Durham, William H. (1991) Coevolution: Genes, Culture, and Human Diversity (Stanford: Stanford University Press).

Hodgson, Geoffrey M. and Knudsen, Thorbjørn (forthcoming), Darwin’s Conjecture: The Search for General Principles of Social and Economic Evolution (Chicago: University of Chicago Press).