Dairy Selection

In yesterday’s post we noted the difficulty people naturally have in grasping the immensity of the timeframe at which evolution occurs. But despite the zoomed-in view our fleeting lifespans impose upon us, we can still detect the occasional tick of the evolutionary clock. Just such an observation has recently been made regarding the genetic trait known as lactose tolerance.

The ability to digest milk depends on the presence of an enzyme called lactase-phlorizin hydrolase in the small intestine. In ancestral humans the production of this enzyme fell off after weaning, as the only source of milk was a child’s mother. But with the domestication of cattle, the ability to digest milk would confer a powerful selective advantage, and researchers have now found that the trait emerged in two disparate populations — one in Northern Europe, one in Africa — as the result of two distinct but convergent mutations that, as a result of the tremendous adaptive value conferred by being able to take advantage of a new source of nourishment, spread rapidly through the two groups. Confidence that selection pressure was the cause of the spread of the mutation is bolstered by the fact that the date of the mutations — about 5,000 years ago for the African group — corresponds well to archeaological dating of the first domestication of cattle in the region.

There will be those, of course, who will dismiss this as mere “microevolution”, and who will doggedly, and dogmatically, continue to deny the Darwinian account of their origins. But macroevolution is nothing more than accumulated microevolution — indeed, the distinction is in no sense a conceptually important one — and we can only hope that such protests and denials will simply seem more and more benighted and desparate as the years go by.

Dennis Mangan also remarks on this latest finding at his excellent website, Mangan’s Miscellany.

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