Wednesday, December 19, 2007

Recent Human Evolution

Until the emergence of agriculture 5,000 to 11,000 years ago, human ancestors lived as hunter-gatherers or foragers. Proponents of "evolutionary psychology" assume that most of our genetic evolution occurred before the transition to agriculture. Since then, there has been much cultural change but almost no genetic change.

But there are some good examples of how cultural changes over the past 10,000 years have brought about genetic evolution. One example is how human populations in dairying cultures have evolved genetically so that adults can digest fresh milk, because their bodies produce the lactose-digesting enzyme lactase. In China and most of Africa, most people cannot digest milk in adulthood because their ancestors did not belong to dairying societies.

Now, new research suggests that rapid genetic evolution over the past 10,000 years--like the evolution of lactose tolerance--might be much more common than was previously thought. An article in THE PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (December 26, 2007) surveys the evidence from genetic differences across human populations that indicate rapid genetic evolution over the past 10,000 years. The authors argue that rapid increasses in human population over this period combined with great changes in cultural and ecological conditions created the circumstances for rapid evolutionary adaptation. This paper has received wide publicity.

Two of the authors of this paper--Gregory Cochran and Henry Harpending--are the authors of a paper published in 2005 on the "Natural History of Ashkenazi Intelligence", published in the JOURNAL OF BIOSOCIAL SCIENCE, 38 (2006): 659-693. The Ashkenazi Jews have the highest average IQ of any ethnic group. Cochran and Harpending argue that this arises from a history of genetic evolution shaped by the demography and social conditions of Ashkenazi Jews in Medieval Europe. The Medieval Ashkenazim were forced into financial and managerial occupations that demand high intelligence. They also showed intense reproductive isolation, because they rarely married outside their group. These two factors created the conditions for rapid genetic evolution favoring high intelligence. Moreover, the high rate of certain genetic disorders (such as Tay-Sachs) among the Ashkenazim suggest that the genetic propensities favoring high intelligence have costly side-effects.

All of this research is highly controversial. But at the very least, it forces us to question the nature/nurture dichotomy, because it suggests that cultural evolution can create the conditions for rapid genetic evolution. As Edward Wilson indicated years ago, human nature cannot properly be understood as predominately genetic or cultural, because it should rather be seen as arising from the complex interaction of genes and culture. Understanding gene-culture coevolution is the final goal for the new Darwinian science of human nature.

Another example of reseach on recent human evolution is Gregory Clark's evolutionary explanation for the industrial revolution in Great Britain in his book A Farewell to Alms. My post on this can be found here.


Kent Guida said...

Thanks for bringing this new work to our attention, and thanks for providing the thoughtful comments on Gregory Clark's book.

Memetic Warrior said...

These discoveries are not in contradiction with the fundamental assumptions of Evolutionary Psychology; EP is devoted to the study of mental modules, that is, instincts at the specie level. EP is a qualitative science, not a quantitative one.

These last time adaptations correspond with one or two gene mutations that improve some already existing phisical or mental capabilities ( sometimes worsening others), but does not develop new ones.

The development of a new mental module/instinct need the coordinated mutations of a number of genes. That requires hundreds of thousands of years, so the assumptions of EP are right for his field of study.

These kind of small changes are very interestinf for other disciplines like medicine and population genétics and even for paleo-anthropology, because it brings new knowledge about the rate of mutation change, but not for EP.