Despite using culture and technology as ways of adapting to new environments, humans, like all other living things on Earth, undergo genetic changes as a response to conditions around them -- or in this case, favorable traits in their genes.
In other words, we're all still evolving.
Most discussion about our evolutionary history focuses on macroevolution, or changes occurring over long periods of time, including why our teeth are smaller when compared with our ancestors' and how our species may have interacted with Neanderthals.
Instead, the study's authors provide an example of microevolution, or changes tracked in a few generations. The team, led by Canadian researchers, studied the small island town of Ile aux Coudres, located in the Gulf of Saint Lawrence in Quebec.
Researchers looked at church records from 1799 to 1940, which provided detailed accounts of marriages, births and deaths. Because the vast majority of families have remained on the island with few newcomers arriving, it was possible to build extensive family trees from the demographic data. The team studied the age at which women are capable of giving birth, a trait that's heritable between generations.
They found that the average age at which women on the island had their first child fell from 26 years to 22 years of age over the time period. But what makes the finding unique -- an example of microevolution -- is the relationship between younger childbirth and family trees. The trend closely follows genetic ties, and it increased over time, suggesting the trait was passed down and favored by natural selection.
But how can scientists rule out social and cultural factors that affect when a woman first gives birth?
Since the small island has a rather egalitarian history, social standing has been less of an issue. In addition, if cultural factors and better nutrition caused the spike in younger mothers, it would be traceable through all women suddenly, not through family lineages over time.
Natural selection, as suggested by a researcher not involved in the study, may have even acted on a group of genes, not just one gene, responsible for sexual maturity, according to a New York Times article.
Culture still matters, though, and one Wired blog post points out that social conditions still allowed for natural selection to occur, meaning conditions were favorable for it to happen.