Testosterone

A composite image shows the facial differences between an ancient modern human with heavy brows and a large upper face and the more recent modern human who has rounder features and a much less prominent brow.
Robert Cieri / University of Utah

About 50,000 years ago, people started developing tools. They started making art, in caves. And they started cooperating. Simultaneously, that's when our faces went from looking like the skull on the left, to the one on the right.

A group of researchers from Duke and the University of Utah are theorizing that the correlation is not coincidence; that, in fact, the changing shape of skulls signals a change in something else that would have made cooperation more likely: A drop in male testosterone levels.

Researchers at Duke University say testosterone affects people’s willingness to take economic risks. Associate professor of psychology and neuroscience Scott Huettel says men and women with high or low levels of testosterone are more likely to take risks in economic situations:

"Testosterone is important, but it’s equally important for men and women it turns out. Your level of testosterone matters quite a lot to how risk-seeking you are, but it matters in much the same for women as it does for men."