Blooming Human Society and Technology Boom Linked to Less Testosterone

Modern humans roamed the planet as early as 200,000 years ago, and yet it was only about 50,000 years ago that advanced tools and art became widespread. Researchers have long wondered why it took so long for humans to create these changes in society and now, they may have the answer. It turns out that lower testosterone could be to blame.

"The modern human behaviors of technological innovation, making art and rapid cultural exchange probably came at the same time that we developed a more cooperative temperament," said Robert Cieri, lead author of the new study, in a news release.

What caused this more cooperative temperament? It turns out it may be down to less testosterone. The researchers measured more than 1,400 ancient and modern skulls and found that when cultural advancements were made, heavy brows were out and rounder heads were in. These changes can be blamed on less testosterone working on their skeletons.

While this theory may seem unusual, it's not the first time it's been put forth. In fact, studies in Siberian foxes showed that animals who were less wary and less aggressive toward humans took on a different, more juvenile appearance and behavior after several generations of selective breeding.

In this particular study, the scientists compared the brow ridge, facial shape, and interior volume of 13 modern human skulls older than 80,000 years, 41 skulls from 10,000 to 38,000 years ago, and 1,367 20^th century skulls. In the end, the researchers found a reduction in the brow ridge and a shortening of the upper face, which are traits that generally reflect a reduction in testosterone.

Currently, researchers aren't sure why there was this sudden reduction in testosterone. Yet this could have helped lead to the modern societies of today. It's possibly that living together and cooperating put a premium on agreeableness and lowered aggression, which could explain why humans were selected for lower testosterone.

"If prehistoric people began living closer together and passing down new technologies, they'd have to be tolerant of each other," said Cieri. "The key to our success is the ability to cooperate and get along and learn from one another."

The findings are published in the journal Current Anthropology.