A paper that is getting some attention at the moment is a critique of evolutionary psychology by Bolhuis and colleagues, titled Darwin in Mind: New Opportunities for Evolutionary Psychology. They critique a number of tenets of the “Santa Barbara school of evolutionary psychology”, including the notion that human psychological mechanisms evolved in response to stable ancestral environments or that there is a universal human nature.
As there has been some commentary on the general point of the article by some other bloggers (check out John Hawks or Razib at Gene Expression), I won’t spend much time questioning the accuracy of the critique or the lack of concrete suggestions by Bolhuis and colleagues. However, the article does have some interesting points on the speed of human evolution.
Bolhuis and colleagues argue that evolution can occur rapidly. They refer to one study which suggests that a trait can shift by one standard deviation within 25 generations (which I am going to have to read):
Evolutionary biologists have also measured the rate of response to selection in a wide variety of animals, finding that evolutionary change typically occurs much faster than hitherto thought. A recent meta-analysis of 63 studies that measured the strength of natural selection in 62 species, including more than 2,500 estimates of selection, concluded that the median selection gradient (a measure of the rate of change of fitness with trait value) was 0.16, which would cause a quantitative trait to change by one standard deviation in just 25 generations. If humans exhibit equivalent rates, then significant genetic evolution would occur over the course of a few hundred years.
Rapid evolution provides the basis for genetic variation between populations, and Bolhuis and colleagues suggest that the brain in particular has been subject to rapid change.
While variation within populations accounts for the bulk of human genetic variation, around 5%–7% of genetic differences can be attributed to variation between populations. Some of the significant genetic differences between human populations have arisen from recent selective events. Gene-culture coevolution may well turn out to be the characteristic pattern of evolutionary change in humans over recent time spans. From this perspective, cultural practices are likely to have influenced selection pressures on the human brain, raising the possibility that genetic variation could lead to biases in the human cognitive processing between, as well as within, populations. In summary, there is no uniform human genetic program.
[H]uman dispersal and subsequent exposure to novel climates, aggregation and exposure to new pathogens, and farming and exposure to new diets are now widely thought to be the source of selection for the spread of many human alleles. Amongst the overrepresented categories in genome-wide scans of recent selection are numerous alleles expressed in the human nervous system and brain. This raises the possibility that complex cognition on which culture is reliant (social intelligence, language, and challenges associated with constructing and adapting to new environmental conditions) have driven human brain evolution. … Gene-culture dynamics are typically faster and stronger and operate over a broader range of conditions than conventional evolutionary dynamics.
While this argument for strong recent selection places the claim that humans have a universal nature in some context, it does not appear fatal to the general concept that many of our characteristics are likely to be common through our common ancestors. However, I do like the consideration of variation, and there is another dimension where it is important and often overlooked. That dimensions is whether, within a single population, did diverse traits co-evolve and now co-exist? The example that always comes to my mind is that of the sneaky dung beetles. While some are following an alpha male strategy of growing large and guarding their females, others are sneaking in from the back with their large testicles and long sperm. Similar strategies are found in some species of deer, crickets, cuttlefish and so on. To understand the adaptive benefit of one particular strategy, there should be recognition of the suite of strategies in which it sits. Sometimes those strategies are part of the variation that selection will erase. At other times, that variation might be the equilibrium point, with the success of any individual tied to the presence of others with different traits.