Sexual And Natural Selection: Why Humans Are Still Evolving

Comparative photo between a masculine-looking (left) and feminine-looking (right) male. Photo from Dienekes' Anthropology Blog.

On Dienekes' Anthropology Blog, he shares with us a study on the correlation between female mate choice (sexual selection) and national health index (DeBruine et al., 2010). Female tend to prefer more masculine-looking males in countries where the national health index is low. Consequently, females tend to prefer more feminine-looking males in countries where the national health index is high. Head over to Dienekes's blog to read about his blog post, "Preference for masculine/feminine-looking men and national health".

With natural selection at work, females are predicted to be much shorter and stouter in the future. Photograph by Hans Neleman/ Getty on Macleans.ca

Also read about "Evolution favours shorter and heavier women—like it or not", an article that foresees the evolution of females to be that of much shorter and stouter. Stephen Stearn, professor of evolutionary biology at Yale University thinks that humans continue to evolve even when we're in a post-industrial society. While there are no large-scale genetic changes, Stearn believes that natural selection is still at work.

“One [could express] the result as: women are going to get shorter and fatter,” he explains. But he prefers a different bent: “There is natural selection against women being slender.” Stearns’s work shows that plumper, shorter women tend to bear more children—who carry on those same traits. His analysis drew on data from the Framingham Heart Study: a survey, begun in 1948, that collected medical information from 5,209 subjects, and monitored them and their offspring for 60 years. 

The weight part of the equation, says Stearns, is straightforward: “A woman has to have about 20 per cent body fat to ovulate and conceive.” But he admits that he “can’t give a good explanation of why they are getting shorter.” A separate study by Open University’s Daniel Nettle found that shorter women are more likely to be in long-term, offspring-producing relationships—perhaps, he hypo thesized, because men evolved to disfavour tall women, who tend to reach puberty later.