That’s the title of a new two-part documentary on PBS. The associated website has all sorts of interesting stuff, including an interview with a geneticist looking at the relationships among the world’s 400 or so breeds. There’s a podcast.
Lactose tolerance: independent origins and strong selective pressure
Michael Kubisch has submitted another post, based on an article in Nature Genetics. Unfortunately the full article and a News and Views piece about it are behind a paywall. However, I’ve done some sleuthing to find a few links that give more details on the story, which I’ve added at the end. As Michael noted, the article is “not about genetic diversity of agricultural species, but how agriculture has affected human genetic diversity”. That’s good enough for us.
The ability to digest lactose, one of the primary carbohydrates in milk, varies widely among adult human populations. In some European countries nearly 90% of individuals can tolerate lactose, while the incidence in some Asian countries is as low as 1%. The inability to digest lactose is caused by a decline in lactase, the enzyme that breaks down lactose into sugars that can be absorbed into the blood stream. This decline starts shortly after weaning and most likely reflects the fact that until animals were domesticated, milk was simply not a staple of human diets. Lactose tolerance, or lactase persistence as it is sometimes called, in turn is facilitated by a continuous production of lactase throughout adulthood. Not surprisingly, lactase persistence appears to be closely linked to whether a population has traditionally practiced a pastoral or an agricultural lifestyle.
This new study examined the incidence of lactase persistence in several African populations. Based on analysis of genetic markers the authors of the study conclude that the trait appears to have evolved not only independently from Europe, but also more than once in Africa itself. Given that the prevalence of the trait is so high in some populations and domestication of milk-producing animals only goes back 12000 years or so, which is a mere blink of an eye in evolutionary times, milk consumption must have provided a significant benefit for human survival.
Those links:
- New York Times: Lactose Tolerance in East Africa Points to Recent Evolution
- Genetic Archaeology.com: Lactose tolerance gene proves Natural Selection in humans
- University of Maryland press release: UMd-Led Team Discovers Gene Mutation for Milk Tolerance in Africans
- Understanding Evolution ((Best of the lot, by far. What a fine site.)): Got lactase?
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Hai chihuahua!
A DNA study suggests that small dogs started to appear about 10,000 years ago as a result of a mutation in a single gene (called IGF-1). I wonder if something similar will be found in other domestic animals.
Domestication
Michael’s post on water buffalo genetic diversity and domestication reminded me that I was intending to point you all in the direction of Dienekes’ Anthropology Blog. Although Dienekes mainly blogs about the genetic diversity and evolution of humans, he does occasionally link to papers on animal domestication and related issues. He has an RSS feed, which makes it easy to monitor his blog. In the past couple of years he has pointed to interesting papers on:
Incidentally, a great paper reviewing the use of genetics and archaeology to document domestication came out last year and you can see the abstract here. Now, what’s really needed is for someone to bring together the human, livestock and crop genetic data.
A new route for pigs and people across the Pacific
The standard story of Pacific colonization is that people and their crops and livestock spread across it in a generally southwestern direction. Scientists from Durham University and the University of Oxford are renavigating the details. They looked at DNA from various pigs across the Pacific, and conclude that their journey may have started in what is now Vietnam. It has always been assumed that the people and their agriculture traveled together as a single package. This research indicates that different parts of the package took different routes.
There’s more detail at a Durham web site about pig domestication, but the actual paper does not seem to be available online yet. Here’s the press release announcing it.