Over millions of years, evolution is changing the way humans look. Over a shorter period, improved nutrition and medical discoveries have meant that people in some parts of the world today are generally bigger and stronger than their ancestors. But we are also losing some abilities that no longer seem useful. The smallest toe, for example, can no longer be moved independently by most people. As recently as Roman times, some people may have been able to “prick up their ears”, moving them slightly towards sounds as some animals can.
Humans are getting taller; they’re also fatter than ever and live longer than at any time in history. And all of these changes have occurred in the past 100 years, scientists say. So is evolution via natural selection at play here? Not in the sense of actual genetic changes, as one century is not enough time for such changes to occur, according to researchers.
Most of the transformations that occur within such a short time period “are simply the developmental responses of organisms to changed conditions,” such as differences in nutrition, food distribution, health care and hygiene practices, said Stephen Stearns, a professor of ecology and evolutionary biology at Yale University.
But the origin of these changes may be much deeper and more complex than that, said Stearns, pointing to a study finding that British soldiers have shot up in height in the past century. ”Evolution has shaped the developmental program that can respond flexibly to changes in the environment,” Stearns said. “So when you look at that change the British army recruits went through over about a 100-year period, that was shaped by the evolutionary past.”
And though it may seem that natural selection does not affect humans the way it did thousands of years ago, such evolutionary mechanisms still play a role in shaping humans as a species, Stearns said.
“A big take-home point of all current studies of human is that culture, particularly in the form of medicine, but also in the form of urbanization and technological support, clean air and clean water, is changing selection pressures on humans,” Stearns told Live Science.
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