Maybe it's agriculture?

Diet and the evolution of human amylase gene copy number variation:

...We found that copy number of the salivary amylase gene (AMY1) is correlated positively with salivary amylase protein level and that individuals from populations with high-starch diets have, on average, more AMY1 copies than those with traditionally low-starch diets. Comparisons with other loci in a subset of these populations suggest that the extent of AMY1 copy number differentiation is highly unusual. This example of positive selection on a copy number-variable gene is, to our knowledge, one of the first discovered in the human genome. Higher AMY1 copy numbers and protein levels probably improve the digestion of starchy foods and may buffer against the fitness-reducing effects of intestinal disease.

From the digest in Nature News:

When the researchers ventured beyond university campuses to sample populations in Africa, Asia, Europe and the Arctic, they noticed a trend. Cultures with diets that included high levels of starch tended to have more copies of the amylase gene than cultures that consumed few starches.

Starch-loving cultures such as the Hadza of Tanzania who rely heavily on tubers and other root vegetables, have 6.7 copies of amylase, on average. While people like the Mbuti, pygmy rain forest hunter-gatherers from central Africa who eat little starch, have 5.4 copies on average.

This shouldn't be a big surprise. Some of justifications sound like those for lactase persistence, "The ability to digest starch may have had the added benefit of cutting down on diarrhoea." The rest of the commentary just writes itself, so I'll just let you go on with your internal monologue....

Page 2 of the supplemental PDF has some population level data (the N's are small of course for some of the groups).

Related: Slow & diverse food.


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Reading the last few articles you have done and sitting back, I just had an "Age of Miracle and Wonder" moment. The fact that we can tell "actively selected" genes in humans, that they correlate with observable traits, that we can even look for multiple copies of genes, and find effects, it is just amazing. Look at the power of evolutionary biology! Compared to 25 to 30 years ago, (when I took my only classes even related to the area...) the concrete knowledge, the depth and resolution of the major frameworks of theory, the power of the gene decoding technology is pretty heady.

Not often do I get that feeling anymore as I get older and it is fun to still feel the rush so I just wanted to share it ^_^.

Compared to 25 to 30 years ago, (when I took my only classes even related to the area...) the concrete knowledge, the depth and resolution of the major frameworks of theory, the power of the gene decoding technology is pretty heady.

the time scale is wrong. think 5 years ago. i started blogging in 2002 on these topics and we're in a different universe. don't even talk about when i was an undergrad....

and quote me on this: you ain't see anything yet. i think the next 5-10 years will be the age of computational genomics as more and more data comes into the pipeline. at some point we'll hit diminishing returns as sequencing gets so cheap that the N's in these studies increase and all populations will be hit. but i don't think we're there yet. and what about DNA extracted from subfossils? we'll probably be able to map gene frequency changes for the past 10,000 years pretty least major genes of interest.