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Modern humans appear in the fossil record about 200,000 years ago, but it was only about 50,000 years ago that creating art and advanced tools became widespread. Becoming nicer, calmer and more feminine might have been a factor in making that happen.

A new study appearing in the journal Current Anthropology finds that human skulls changed in ways that indicate a lowering of testosterone levels at around the same time that culture was blossoming.

The study, which is based on measurements of more than 1,400 ancient and modern skulls, makes the argument that human society advanced when people started being nicer to each other, which entails having a little less testosterone in action.

Heavy brows were out, rounder heads were in, and those changes can be traced directly to testosterone levels acting on the skeleton. What researchers can't tell from the bones is whether these humans had less testosterone in circulation, or fewer receptors for the hormone.

The research was led by University of Utah biology graduate student Robert Cieri. The research team also included Duke University animal cognition researchers Brian Hare and Jingzhi Tan, who say this argument is in line with what has been established in non-human species. The research builds on work Cieri did for his senior honors thesis while he was student at Duke.

There are a lot of theories about why, after 150,000 years of existence, humans suddenly leapt forward in technology. Around 50,000 years ago, there is widespread evidence of producing bone and antler tools, heat-treated and flaked flint, projectile weapons, grindstones, fishing and birding equipment and a command of fire. Possible reasons include a brain mutation, cooked foods, the advent of language and population density.

Cieri told The Salt Lake Tribune that he thinks living in close quarters had a lot to do with it.:

Humans didn’t became more girly in order to evolve culturally and intellectually. Rather, features considered hyper-masculine began to go, he said.

"It’s not necessarily that people are acting more like females, it’s just kind of this overly aggressive, intolerant phenotype was maybe selected against," Cieri said.

He said it’s possible testosterone began to dive as humans grew more populous and began living in more tightly packed conditions.

"It could have happened because as population density started increasing people were living closer together and had to get along," Cieri said.

This post originally appeared at Wonky News Nerd.
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