Wednesday, December 10, 2008

Gene-culture co-evolution and evolutionary psychology

How much do human populations differ from each other in real, functional terms? The question remains open, but an answer is starting to unfold. In 2007, a team led by anthropologist John Hawks found that natural selection seems to have modified at least 7% of the human genome over the last 40,000 years, i.e., during the period when modern humans spread out of Africa and peopled the other continents. In addition, as they moved into these different physical and cultural environments, the pace of genetic change seems to have speeded up, particularly after the advent of agriculture 10,000 years ago. The rate of change may then have been over a hundred times what it had been during most of human evolution (Hawks et al., 2007)

We do not fully know the nature of these recent genetic changes. John Hawks suggests they may reflect adaptations to new ecological and cultural settings, specifically to cold, to new diets (cereals, milk, etc.), to new epidemic diseases associated with the spread of agriculture (smallpox, malaria, yellow fever, typhus, cholera), and to new forms of “communication, social interactions, and creativity.”

There thus seem to have been multiple EEAs in relatively recent times, and not simply one situated in the Pleistocene. Some of them would correspond to the different physical environments that modern humans moved into as they spread out of Africa 40 to 50 thousand years. Most however, seem to have arisen in the past 10 thousand years and correspond to different cultural environments.

John Hawks is certainly not the first one to suggest that culture has been a key part of the human adaptive landscape. Usually referred to as ‘gene-culture co-evolution’, this paradigm has had many proponents, notably Pierre van den Berghe, Charles Lumsden, and E.O. Wilson. It has nonetheless remained marginal, even among evolutionary psychologists. This is partly because of the influence of John Tooby and Leda Cosmides, whose influence was critical during the early years of evolutionary psychology:

It is no more plausible to believe that whole new mental organs could evolve since the Pleistocene—i.e., over historical time—than it is to believe that whole new physical organs such as eyes would evolve over brief spans. It is easily imaginable that such things as the population mean retinal sensitivity might modestly shift over historical time, and similarly minor modifications might have been made in various psychological mechanisms. However, major and intricate changes in innately specified information-processing procedures presentover brief spans of historical time. (Tooby & Cosmides, 1989)

In a more recent article, they have backed away from this position: “Although the hominid line is thought to have originated on edges of the African savannahs, the EEA is not a particular place or time.” Each biological adaptation has its own EEA, which is simply a composite of whatever selection pressures brought it into being (Tooby & Cosmides, 2005). There are thus potentially as many EEAs as there are adaptations. It follows, then, that some EEAs may have existed later in time than others.

How much later? Tooby and Cosmides considered complexity to be one limiting factor. The more complex the adaptation, the more genes it would involve, and the longer the time needed to coordinate the evolution of all those genes. Therefore, recent biological evolution has probably only involved simple traits, certainly nothing as complex as mental ones. Such traits could have arisen only through a faster process, notably cultural evolution.

The problem with this argument is that complex traits do not arise ex nihilo. They arise through modifications, deletions, or additions to existing traits. And such changes can occur through a single point mutation at a regulatory gene. As Harpending and Cochran (2002) point out:


Even if 40 or 50 thousand years were too short a time for the evolutionary development of a truly new and highly complex mental adaptation, which is by no means certain, it is certainly long enough for some groups to lose such an adaptation, for some groups to develop a highly exaggerated version of an adaptation, or for changes in the triggers or timing of that adaptation to evolve. That is what we see in domesticated dogs, for example, who have entirely lost certain key behavioral adaptations of wolves such as paternal investment. Other wolf behaviors have been exaggerated or distorted.

Gene-culture co-evolution also presents difficulties that are inherent to the paradigm itself:

1. The linkages between genes and culture tend to be remote, indirect, multiple, and complex. There are some straightforward ones, such as between lactose intolerance and consumption of dairy products, but such linkages are probably unrepresentative of gene-culture co-evolution.

2. With only a few minor exceptions, gene-culture co-evolution is specific to humans. Cross-species comparisons, so common in other fields of evolutionary study, are thus of little help (van den Berghe & Frost, 1986).

These difficulties are not insuperable. To some degree, they reflect an unconscious desire to study human evolution with the same conceptual tools that have been used to study the evolution of other species. Other tools will have to be developed, or simply borrowed from the social sciences of psychology, sociology, and anthropology. Thus, there are no real barriers to renewed use of this paradigm, particularly as we move beyond the single-EEA model and investigate this 7% of the human genome that has apparently changed over the past 40,000 years.

References

Harpending, H. & G. Cochran. (2002).
"In our genes", Proceedings of the National Academy of Sciences, 99(1), 10-12.

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, & R.K. Moyzis. (2007).
Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA), 104, 20753-20758.

Tooby, J. & L. Cosmides. (2005). Conceptual foundations of evolutionary psychology, in: D. M. Buss (Ed.) The Handbook of Evolutionary Psychology, Hoboken, NJ: Wiley, pp. 5-67.

Tooby, J. & L. Cosmides. (1989). Evolutionary psychology and the generation of culture, Part I. Theoretical considerations, Ethology and Sociobiology, 10, 29-49.

van den Berghe, P.L., & Frost, P. (1986). Skin color preference, sexual dimorphism and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies, 9, 87-113.


6 comments:

Tod said...

However, major and intricate changes in innately specified information-processing procedures present in human psychological mechanisms do not seem likely to have taken place over brief spans of historical time.
(T&C pdf is playing up)

Tod said...

John Hawks suggests they may reflect adaptations to new ecological and cultural settings, specifically to cold, to new diets (cereals, milk, etc.)

Whatever the differences they do not seem to have stemmed from adaptation to a cereal diet. Africans seem to suffer the same ill effects Cereal Grains:Humanity’s Double-Edged Sword,Loren Cordain i.e. rickets. Cordain does not think we are much adapted to dairy produce either Dissociation of the glycaemic and insulinaemic responses to whole and skimmed milk.
Here is Dr. Cordain's hypothesis on a genetic adaptation balancing the putative UV destruction of Folic Acid with light skinned synthesis of Vit. D. Ultraviolet radiation represents an evolutionary selective pressure for the south-to-north gradient of the MTHFR 677TT genotype
White skinned women have been intensively sunbathing for decades, where are the pregnancy problems or Folic acid deficiency among them? 5-Methyltetrahydrofolate inhibits photosensitization reactions and strand breaks in DNA
"We demonstrate that 5-methyltetrahydrofolate (5-MTHF, the predominant folate in plasma) is also a potent, near diffusion limited, scavenger of singlet oxygen and quencher of excited photosensitizers. Both pathways result in decomposition of 5-MTHF, although ascorbate can protect against this loss. In the absence of photosensitizers, 5-MTHF is directly decomposed only very slowly by UVA or UVB. Although synthetic folic acid can promote DNA damage by UVA, submicromolar 5-MTHF inhibits photosensitization-induced strand breaks. These observations suggest a new role for reduced folate in protection from ultraviolet damage and have bearing on the hypothesis that folate photodegradation influenced the evolution of human skin color.—
Cold adaptation would mainly be in the mitochondrial DNA wouldn't it.
Did Neanderthal cells cook as the climate warmed?
If modern humans coped with the cold by using technology rather than adapting their bodies then few of the differences will be due to such cold adaptations. A form of selection other than the one John Hawks mentioned is mainly responsible as far as I can see it.

Tod said...

Is there anything in Geoffrey Miller's idea of g being a manifestation of a generalised fitness factor f? Might adaptation to sexual selection have been originally responsible for increasing g?




Criticism of Reproductive conflict and the separation of reproductive generations in humans has centred on how common patrilocality is/was among hunter-gatherers. Are daughters-in-law to blame for the menopause?
"Kristen Hawkes, at the University of Utah in Salt Lake City, disputes whether human migration patterns are really female-biased as Cant describes them. "He misrepresents the human data he cites." She says that studies of modern hunter-gatherers show that many young females only leave their natal home after they have had a couple of babies,"

Tod said...

to new epidemic diseases associated with the spread of agriculture This seems to be correct. I think MTHFR 667 T has been shown to be related to infectious disease.

Methylenetetrahydrofolate reductase 677 T allele protects against persistent HBV infection in West Africa

(Sorry if I've gone a bit over the top with comments)

Peter Frost said...

Hi Tod,

Sorry for the delay in commenting (I'm tied up writing a chapter for a book).

I think John Hawks was simply throwing out whatever speculations were already in the literature. I suspect most of the genetic changes are linked to behavioral and attitudinal predispositions, but most of the literature tends to focus on diet or cold adaptations.

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