Humans still evolving...25 Oct 2009
Time has a story about Stephen Stearns and colleagues’ work characterizing ongoing selection using the Framingham Heart Study sample:
If these trends were to continue with no cultural changes in the town for the next 10 generations, by 2409 the average Framingham woman would be 2 cm (0.8 in) shorter, 1 kg (2.2 lb.) heavier, have a healthier heart, have her first child five months earlier and enter menopause 10 months later than a woman today, the study found. "That rate of evolution is slow but pretty similar to what we see in other plants and animals. Humans don't seem to be any exception," Stearns says.
I haven’t had a chance to see the new study yet, and I’ll do a little review when I get it. Jerry Coyne has some more information based on a preprint.
My students have heard me say many times that it would take a sample of thousands of people to test the hypothesis of neutrality within today’s population. Well, Framingham is one such sample, and it’s not surprising that some things would be found significantly to affect fitness.
The Time article mentions our work on recent evolution in a very positive way. Of course, the Framingham sample isn’t suitable for testing what has been going on during the last 40,000 years; it is about mass selection on phenotypes in the present American population. That will involve mostly selection on standing variants, things that are already common in the population. Some of those may be things that were increasing in the past, others not – some may even be reversals in direction compared to pre-industrial times. And there’s no predicting how they might change in the future, as we continue to change our environment out from under ourselves.
I’ve seen a few comments that we shouldn’t trust the sample because it’s unrepresentative, too small, etc. I think people may be overlooking the fact that the Framingham Heart Study is bigger than the census sizes of many species in nature. You can detect selection on phenotypes in this sample, and they surely know the heritabilities of many of them. But I’ll have to see the paper.