The evolution of the contemporary human species is often portrayed as a slow process over many tens of thousands of years that culminated in our now-fixed modern state and form. But research from the University of Edinburgh (U.K.), Université du Québec à Montréal and Université de Sherbrooke in Canada suggests that the genetic mechanisms by which humans evolved continue to operate.

Their 2011 study published in Proceedings of the National Academy of Sciences of the United States of America (PNAS), “Evidence for Evolution in Response to Natural Selection in a Contemporary Human Population,” examined an isolated French-Canadian population that grew from 30 families in the mid-1700s to more than 1,500 people in 1950 to see if human evolution persists in recent generations. Demonstrating continuing evolution, the authors state, may have broad implications for “the accuracy of forecasts, for instance those pertaining to demography or epidemiology, and on which public policies may rely, could well depend on our knowledge of contemporary evolution.”

The study’s findings include:

• Tracking the age of first reproduction (AFR) — what the researchers describe as a “good candidate for an evolving trait in humans” — over the nearly 200-year period indicated that “selection indeed strongly favored women with earlier AFR” and that “women who began reproducing at a younger age also tended to stop at a younger age.”
• The “women giving birth to their first child around the 1930s were about 4 years younger (from 26 to 22 years old) than those who began to reproduce around 1800.”
• Many “factors operated on the island in opposition to socioeconomic or cultural trends operational at a larger scale [and] provide evidence that those changes resulted, at least partly, from a micro-evolutionary response to natural selection on AFR.”
• Controlling for many factors, evidence showed that the “AFR was also highly heritable and genetically correlated to fitness, predicting a microevolutionary change toward earlier reproduction.”
• However, “the advancement of age at maturity, as well as increases in fertility, may reflect plastic responses to improvements in nutritional conditions, such as those observed during the 19th and 20th centuries in Western societies.”

The researchers conclude that the findings support the “idea that humans are still evolving. It also demonstrates that microevolution is detectable over just a few generations in long-lived species.”

Tags: science, parenting

By Rozanne Larsen | December 8, 2011