In a report published online 26 October in the Proceedings of the National Academy of Sciences, Stearns and his colleagues documented natural selection in 2238 U.S. women. The women were subjects in the Framingham Heart Study, which has tracked the health of thousands of people in Framingham, Massachusetts, since 1948. The scientists searched for traits that were correlated with having a higher number of children. Then they checked to see whether those traits tended to be passed down from mother to child -- in other words, whether they were genetically based.
The scientists discovered that a handful of traits are indeed being favored by natural selection. Women with a genetic tendency for low cholesterol, for example, had more children on average than women with high cholesterol. A greater body weight was also linked with greater reproductive success, as was shorter height, lower blood pressure, an older age at menopause, and having one's first child at an earlier age.
Stearns and his colleagues now know which traits are selected in the women of Framingham, but they have yet to determine exactly what advantage each trait confers -- a situation that evolutionary biologists often face when documenting natural selection. Nevertheless, based on the strength of the natural selection they have measured, the scientists predict that after 10 generations, the women of Framingham will give birth, on average, a few months younger than today, have 3.6% lower cholesterol, and will be 1.3% shorter.
Of course, even this prediction is subject to change. Women with higher cholesterol may eventually be able to enjoy higher fertility rates thanks to cholesterol-lowering drugs, says Stearns, wiping out the differences in reproductive rates. "Selection is always operating," says Stearns, "but the traits on which it operates shift with ecology and culture."
Wednesday, December 9, 2009
The Future of Human Evolution
Interesting essay by Carl Zimmer on the future evolution of humans. A snippet: