Evolution Says You're Weaker and More Disease Prone Than Your Ancestors - U.S. News & World Report

Skeletons of a chimpanzee, left, a modern human, center, and a Neanderthal are displayed at the Hall of Human Origins of the American Museum of Natural History.

Humans are growing weaker, more disease prone, and just might be developing some manners, according to a new study that asserts humans are still evolving according to Charles Darwin's natural selection theory.

Modern medicine and a move away from an agrarian society have made the hunter-gatherer traits that were once necessary to survive obsolete, according to Alexandre Courtiol, the German scientist and lead author of the report, which was published Monday in Proceedings of the National Academy of Sciences. Courtiol says that thousands of years ago, people died from genetic illnesses that are no longer death sentences with the help of modern medicine. That in turn means people can pass along their genes to their children before they die.

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"What we found was evolution did not stop 10,000 years ago as some scientists thought. In the mid 1800s, the strength of selection was very high—they're very comparable to animal species," he says.

Courtiol also says that humans have been evolving away from the original hunter-gatherer Homo sapiens that appeared about 200,000 years ago. In fact, he says we may have evolved far enough to consider ourselves an entirely new species.

"The change from one species to another is something you can only notice with the perspectivity of time," he says. "If we could travel back in time to meet early humans, I'm not sure if we'd be able to reproduce with the people of the time."

Several scientists have proposed that humans have stopped evolving according to natural selection—the small genetic advantages that make an individual more likely to have children—due to widespread monogamy that limited the amount of sexual partners humans had. Courtiol's study found that even in monogamous populations, humans still evolve according to natural selection.

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The team, using very thorough birth and death records from the mid-1800s that were kept by Finnish churches, found that people who were able to live past the age of 15 were best able to pass along their genes to the next generation, which may have weeded out certain genetic conditions. Men were also 25 percent more likely to pass along their genes than their partners, because they were more likely to remarry after a partners' death, according to the records.

Courtiol says the story is different in modern times. To accurately demonstrate natural selection—perhaps the key component of species evolution—scientists need to study an entire population's birth and death records and try to determine the small advantages that made it more likely for a person to have a child. But by assessing cultural and medicinal trends, he says it's likely women are no longer going for the biggest, burliest guy they can find.

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"Traits influencing survival are no longer evolving, because with medicine, they're less important today," he says. "What's more important today is what makes you able to find a partner and how many offspring you have. Today we're probably evolving psychological personality traits, which are more important today than they used to be."

So while people might be passing along genes that turn children into impeccable guitar players or star athletes, they are also passing along things like susceptibility to cold weather or lackluster endurance.

"Natural selection is a bit like politics, there's tradeoffs. You can't be good in every aspect," Courtiol says. "If we're selecting based on cognitive traits, you put less stock into your physical body, your strength."