I am not a big fan of Twitter, though the WEIT posts go out on it. I hate the word “tweet,” which rankles as much as “blog,” and constant personal “tweeting” seems to me more than a tad solipsistic. But how could I not post this “tweet” from the Evolution 2011 meeting feed (#evol11):
If you’ve read WEIT, you’ll know that those human populations with a history of “pastoralism” (raising cows, sheep and goats for milk) have a high frequency of genes for lactose tolerance compared to those human populations that don’t consume much milk. Further, the allele for lactose tolerance increased in frequency only in the last 10,000 years, which parallels the time when pastoralism began. (The gene, by the way, is one that allows the enzyme lactase, which breaks down lactose into sugars, to keep being expressed into adulthood. That gene is usually turned off after childhood, when, historically, people no longer nursed.)
It’s a really good example not only of evolution in “real” (or semi-real) time, but also of gene/culture coevolution: a change in human culture—the domestication of milk-yielding mammals—has created a “natural” selective pressure that changed our genes. This, of course, is due to the tremendous reproductive advantage of having access to such a rich food source, which you can gain only if you can digest it. (The reproductive advantage of digesting milk in a pastoral population is a whopping 10%!). You can read more about this system at the Understanding Evolution site.
Apparently, the same genetic changes have occurred in cats commensal with humans. Clearly, cats have been fed milk by their pastoral owners for a considerable amount of time: cats appear to have been domesticated between 8,000 and 5,000 years ago.
Self aggrandizing note: Allen Orr and I have co-signed several copies of our book, Speciation, on sale at the Sinauer booth at these meetings. Jointly signed copies are rare—Orr and I are rarely at the same place at the same time—so pick up one of these rarities now. (Note: there is no surcharge!)