It wasn鈥檛 so long ago that there was something of a consensus on recent human evolution, or the lack of it. The belief was that culture had elevated our species above Darwin鈥檚 鈥渉ostile forces of nature鈥�, stopping natural selection in its tracks 50,000 years ago. But that view has increasingly been questioned over the past 10 years.
Those who say selection stopped long ago point to vast improvements in life expectancy. To be sure, life expectancy has increased and many dread diseases have receded. But to pass on their genes to the next generation, people must not only survive, but reproduce. Differences in reproduction are differences in .
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This idea underpins a new study by Jonathan Beauchamp at Harvard University, which looked at genetic variants associated with traits including educational attainment. It suggests that natural selection has been at work on people in the US in the 20th century.
To try to shed light on differences in fitness, demographers and evolutionary scientists are exploiting data from long-term health studies covering thousands of people in the US, the UK and other countries.
Beauchamp tapped into the 20,000-person , which is augmented by . Looking at people born between 1931 and 1953, he found that in both men and women, .
That much may seem obvious. For a century, Americans have been foregoing family size and early child-rearing for more education. Globally, this change is part of what is known as the .
Link with genetics
What is new is the tie to genetics. Educational attainment is not strongly heritable, with in attainment. But Beauchamp found that gene variants predictive of attainment, including many active in early brain development, were nearly as strongly predictive of reduced reproduction.
Beauchamp concluded that natural selection was acting on Americans, albeit slowly. Its impact is equal to a small decline in attainment amounting to a month and a half less education per generation, and is in any case swamped by the many other factors driving up educational attainment at the same time.
Of course Beauchamp鈥檚 study only covers a limited sample of US citizens. In addition, participants could be women aged 45 or men in their early 50s, which seems too young to judge lifetime reproduction. There are also suggestions that the number of grandchildren or great-grandchildren is a better measure of fitness.
However, it is not outlandish to imagine that natural selection may still be acting in this way in the US and beyond, given the pace of change. In 1940, only . By 2000 this was approaching 90 per cent.
Our distant ancestors never knew environments where it made sense to delay reproduction for years to reap the rewards of an extended education. We may be doing more with education policies than shaping tomorrow鈥檚 well-qualified workforce. It turns out we may be shaping the course of human evolution.
PNAS
