Sunday, December 10, 2006

Fast, convergent evolution witnessed in East Africans

NYT's Nick Wade reports that lactose tolerance in East Africans appeared as recently as 3,000 years ago. It spread through Europe somewhere between 5,000 and 6,000 years ago.

Lactose intolerance in the African heat and drought is conceivably a severe disadvantage, not only in limiting the amount of available fluid intake, but also in causing bowel problems and water loss in those unable to tolerate it. Such an advantage should spread like wildfire. In evolutionary terms, 3,000 years approximates that pace (though the time thought to be required for major evolutionary change continues to lessen)--about four-fifths of African Tutsis (historical herders) are lactose tolerant.

ASPM and microcephalin have also cropped up recently in varying degrees by ancestral population. Stubbornly feral silver foxes have become as amicable toward humans as golden retrievers in a mere thirty generations. That comes to about 750 years for us--less time than Dr. Cochran and crew hypothesize it took Ashkenazi Jews to obtain a one standard deviation advantage in intelligence over their Gentile brethren.

We're a work in progress--moving at difference paces and in different directions. The differences are more than skin deep.


JSBolton said...

This is one of the quirky aspects of biology; when you would expect one best mutation to just spread and spread, instead we're presented with now already four independent emergences of the same character.
There must have been some steep isolating barriers, or how could there have arisen this many, when they could have borrowed one from another?
That Africa, even within its own confines, allows for independent evolutions of this magnitude is striking.
Recall that independent means that one man has hundreds of millions of descendants in the case of the European one, and tens of thousands or millions with the African ones.
This is so to such extent, as the article describes, European populations have gone to 99% carriers in some countries.
That haplotype block is said to be ~1 million DNA units long, as if it had just spread so thoroughly, that it was found breeding only with its matching carriers, and such that recombination in millennia, has had negligible occasion to break up its extraordinary length.
Anyone who now says natural selection is insignificant in man during the age past the divergence of the great races, has now some facts to reckon with, which decidedly contradict his feeling of what must be.

Fat Knowledge said...

Good stuff.

Another one I am interested in is alcohol metabolism. I bet you see quite a few differences between various races. 1/2 of Asians get the 'flush face' when drinking due to a bad gene coding for acetaldehyde dehydrogenase. I might be over simplifying, but Europeans used to use alcohol to sterilize their water while Asians boiled theirs.

Will be interesting to see what they find next.