Men

Image of Glen Warren and his three children
Glen Warren

Glen Warren vividly remembers the first moments of single fatherhood: he was standing in the living room of his new mobile home with his three kids, and he quickly realized that he had no idea how to make them dinner. 

In the coming years he learned how to piece together meals, filed for child support, and worked multiple jobs to put food on the table. And through all of this, he became increasingly certain about one thing: fatherhood is incredibly important. 

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.