Natural Selection Leaves Fresh Footprints on a Canadian Island
From parish records in a French-Canadian island, researchers have uncovered what may be the most recent known instance of human evolution in response to natural selection.
The island, Île aux Coudres, lies in the St. Lawrence River 50 miles northeast of Quebec. Its church registries hold an unusually complete record of births, marriages and deaths. From this data, a team of researchers led by Emmanuel Milot and Denis Réale of the University of Quebec at Montreal have extracted the histories of women born on the island between 1799 and 1940.
Over this 140-year period, the age at which a woman had her first child — a trait that is highly heritable — fell to 22 years, from 26. Because of this change, women on average had four more children during their reproductive lifetime, the researchers report.
The finding “supports the idea that humans are still evolving,” the researchers write in Monday’s issue of The Proceedings of the National Academy of Sciences.
Dr. Milot said statistical tests allowed the researchers to distinguish between the effects of natural selection and those of cultural practices affecting the age of marriage.
“The common view is that evolution is a slow process,” he said. “But evolutionary biologists have known for several decades that evolution can occur fast.”
It was long assumed that people protected themselves from the forces of natural selection when they learned to put a roof over their heads and grow their own food. Data from the human genome in the last decade has shown this assumption is untrue: The fingerprints of natural selection are visible across at least 10 percent of the genome.
And this is selection that occurred in just the last 25,000 to 5,000 years, because the signal from older episodes of selection is muffled by constant mutation in the DNA sequence…