Stout women pass on genes, study finds

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No caption. Photo by Erica Blonde.

The theory of evolution suggests that mankind evolved from apes. But are humans still evolving?

A team lead by Yale researcher Stephen Stearns says yes. They found that women’s fertility still affects natural selection. By tracking 2,238 post-menopausal women living in Framingham, Mass. over a period of 60 years, Stearns and his team found that stout, slightly plump women and women with lower blood pressure and cholesterol tended to have more children.

Their children, in turn, tended on average to be even stouter and plumper.

“Variations in reproductive success still exist among humans, and therefore some traits related to fertility continue to be shaped by natural selection,” Stearns said.

Stearns and his team examined the women’s vital statistics, such as height, weight and blood pressure. These women were part of the Framingham Heart Study, which was started in 1948 by Thomas Dawber. The researchers used post-menopausal women, Stearns said, because they would no longer bear children.

The researchers concluded that if these trends were to continue in Framingham over the next 10 generations, the average woman in the town would be eight-tenths of an inch shorter, 2.2 lbs heavier, have their first child five months earlier and enter menopause 10 months later than a woman today.

By tracing family pedigrees, Stearns and his team found that low blood pressure and cholesterol levels are passed on through the mother. Because women with low body fat levels do not ovulate, Stearns said, these characteristics can only be passed on through heavier women.

While the effects of evolution in each generation are small, the results add up over time, said Boston University researcher Raju Govindaraju, a member of Stearns’ team.

“In very simplistic terms, if there is differential reproduction and mortality in any family, and hence variation in family size, then we could say there is a potential for evolution,” Govindaraju said.

Although funding is limited, Govindaraju said, the team is also studying the effects on evolution of men. In the near future, the team hopes to publish a paper on the effects of evolution of men, Stearns said. Unlike women, men are not being naturally selected for better cardiovascular health or for longer life spans. Instead, men are having their first children at earlier ages.

The researchers are also branching out into genetic research, Stearns added. Stearns said his team hopes to establish a link between fertility and disease resistance. They would also like to examine how interactions between genes affect cholesterol levels and height, he added.

In addition to Stearns and Govindaraju, the research team includes postdoctoral researcher Sean Byars and University of Pennsylvania demographer Douglas Ewbank.

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