Evolution’s Path May Lead To Shorter, Stouter Women Who Give Birth Earlier

From a Yale press release:

Yale University researchers have detected the effects of natural selection among two generations of contemporary women and predict their descendents will be slightly shorter and chubbier, have lower cholesterol and blood pressure and have their first children earlier in life.

The predictions, which were made in the Oct. 19 online edition of the Proceedings of the National Academy of Sciences, were based on an analysis of women who have participated in the famous Framingham Heart Study, that began in 1948. The results illustrate the medical value of evolutionary biology principles, 150 years after Darwin published The Origin of the Species, the authors say.

“The idea that natural selection has stopped operating in humans because we have gotten better at keeping people alive is just plain wrong,” said Stephen C. Stearns, senior author of the paper and Edward P. Bass Professor of Ecology and Evolutionary Biology.

The reason is that traits that enable women to have children will continue to be subject to selection. As a first step, the Yale researchers measured the individual reproductive success of two generations of more than 2000 women who participated in the Framingham study and had reached menopause. They then surveyed the traits that conferred reproductive success. After adjusting for environmental factors such as income, education and lifestyle choices such as smoking, the researchers estimated the heritability of traits by applying correlations among all relatives. They also adjusted for the indirect effects of selection by measuring the impacts the traits have on each other – such as whether high blood pressure is correlated with lower or higher age of sexual maturity.

The statistical analysis allowed researchers to predict which of those traits were likely to be conferred by natural selection upon the third generation of women participating in the Framingham study. The results showed that the effects of natural selection are slow and gradual, but trend towards shorter, chubbier women with lower blood pressure and cholesterol and who give birth earlier in life. For instance, the women in the third generation of the study are predicted to begin their periods a month earlier and enter menopause a month later than their mothers and grandmothers.

However Stearns points out that the rate of change driven by natural selection found in this group of women does not differ much from rates observed in nature.

“The paper drives home the point that humans aren’t different, that we are evolving at about the same average rate as other life on the planet,” Stearns said.

Sean G. Byars, a post-doctoral researcher at Yale, was lead author of the paper. Researchers from the University of Pennsylvania and the Boston University School of Medicine contributed to the paper.

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0 thoughts on “Evolution’s Path May Lead To Shorter, Stouter Women Who Give Birth Earlier

  1. Yeah… short squatters with flat heads on which a man can rest his drink. Gentlemen, it sounds like we’re going to be halfway there soon. In light of this good news, please allow me to propose a toast to the inherent efficiency of nature.

  2. It’s an interesting study, but I think it’s premature to extrapolate the trends in one town to the entire world, or even the entire country.

  3. Gruebait shares my concern about this study. Seems like the dataset is way too small to make the extrapolations it does.

    (Oh — bring a lantern. Grues hate light. Just a protip from an old hand.)

  4. More than 2000 women is not such a small dataset. Remember that they’re extrapolating future evolutionary trends from current reproductive success combined with the heritability of the traits in question. That’s a perfectly valid thing to do, and something that can indeed be done on short time scales.

    However, it must be mentioned that short-term evolutionary trends often change in time. There’s also the problem that some of these traits may reduce future reproductive success (e.g. having menopause later may lead to less genetically-fit offspring). So it should be taken with a grain of salt, but I don’t think lack of sample size is a reasonable objection.

  5. For once, I’m not sure they should control for income. If tallness makes you richer, and being richer improves your odds of producing progeny, they might have missed that.

    Also, I wonder how the fact that sexual selection favors tall males plays out. You had to find genes that make women short and men tall. Not impossible, certainly. But a more restricted set of evolutionary paths than just making everybody short, methinks.

  6. Sexual dimorphism amongst miniscule male spiders and giant female ones, the latter eating the former if foreplay isn’t adequate for their tastes, comes to mind. Dimorphism can’t be that hard to select for, given the differences we can see in just about any animal species you could name.

  7. Jason Dick:

    More than 2000 women is not such a small dataset.

    It’s not necessarily the number of women. I agree with catgirl’s concern over the participants being from one town. People from different regions will vary, nevertheless people from one fairly small city relative to people from different regions of the country/world. I think it’s a valid reason to be critical of the study.

  8. Two generations, totalling two thousand women, all from the same town, might be convenient for developing an idea where the species would go if everyone else in the entire damn world got wiped out or that town got shot off into space, either way causing a speciation event. Otherwise, no. This is a study whose data doesn’t actually tell us anything about the future of humanity so much as examines what might happen if humanity speciated in a region with specific selection criteria.

  9. I am 5′ 6″ . . .my daughter is over 6 feet tall. I had my first child at 23. She is 26 and has yet to show any interest in members of the opposite sex as anything other than patsies to buy her stuff online. Plus she told me when she was 14 that if the only way to avoid spawning was to be a lesbian, she would be a lesbian.

    I can’t think of any one I know with a daughter who is not at least an inch taller . . and last I heard, humans are getting taller. Of course, if you have a daughter you results might vary.

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