09 June 2009

Fast Human Evolution Tweaked by Migrations

Image Source Impact Lab
When groups of humans migrate into different environments, their extended genome begins to adapt to the new environment almost immediately. How does this happen? Geneticists do not know, precisely, but they are betting that this fast-adaptation occurs by other means than traditional natural selection.
In recent years, geneticists have identified a handful of genes that have helped human populations adapt to new environments within just a few thousand years—a strikingly short timescale in evolutionary terms. However, the team found that for most genes, it can take at least 50,000-100,000 years for natural selection to spread favorable traits through a human population. According to their analysis, gene variants tend to be distributed throughout the world in patterns that reflect ancient population movements and other aspects of population history.

“We don’t think that selection has been strong enough to completely fine-tune the adaptation of individual human populations to their local environments,” says co-author Jonathan Pritchard. “In addition to selection, demographic history — how populations have moved around — has exerted a strong effect on the distribution of variants.”

To determine whether the frequency of a particular variant resulted from natural selection, Pritchard and his colleagues compared the distribution of variants in parts of the genome that affect the structure and regulation of proteins to the distribution of variants in parts of the genome that do not affect proteins. Since these neutral parts of the genome are less likely to be affected by natural selection, they reasoned that studying variants in these regions should reflect the demographic history of populations.

The researchers found that many previously identified genetic signals of selection may have been created by historical and demographic factors rather than by selection. When the team compared closely related populations they found few large genetic differences. If the individual populations’ environments were exerting strong selective pressure, such differences should have been apparent.

Selection may still be occurring in many regions of the genome, says Pritchard. But if so, it is exerting a moderate effect on many genes that together influence a biological characteristic. “We don’t know enough yet about the genetics of most human traits to be able to pick out all of the relevant variation,” says Pritchard. _ImpactLab_(from sciencenews)
Scientists are just beginning to understand the significance of the small differences in genotype between extended breeding populations of humans. Because phenotypic differences are significant -- not just morphologically and in terms of physical performance, but in behavioural and cognitive characteristics such as intelligence, executive function, etc. -- between human populations, it is obvious that the slight genotypic differences that exist are meaningful. Scientists need to learn more about how human populations diverged, and what it means for the future.

Clearly the evolutionary stresses presented to isolated villagers living at 10,000 feet in the Andes are much different than evolutionary stresses to coastal city-dwellers in a modern society. Even inside that coastal city, if distinct breeding populations exist within quasi-isolated communities, evolutionary stresses will be somewhat distinct -- and lead to further divergence.

Given the "neo-tribalist" emphasis of the modern political, academic, and popular societal lebensreich, the equalising forces of assimilation have been obstructed by forces of post-modern political correctness and identity dogma. Electing pro-affirmative action presidents and selecting pro-affirmative action Supreme Court justices only hastens the trend toward neo-divergence of core breeding populations.

The level of inter-breeding between populations may seem to contradict this idea, but in reality inter-breeding often has the opposite effect -- enhancing a sense of "separateness" and neo-segregation. A good look at Obama's first auto-biography should illustrate the point well. ("Am I black enough ...?") In the black community of the US, one often finds an elite strata that is composed largely of mixed-race persons who are often more stridently opposed to physical and social assimilation (Reverend Wright) than a typical American black chosen at random.

It is an interesting dynamic, and one that does not lend itself to a closing of gaps of intelligence or executive function. To accomplish that, we will need to understand a lot more about the subtle genetics of differences, and how the (chosen and unchosen) environment plays into that subtlety.

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