A study conducted by researchers from Duke University and the University of Utah revealed that a drop in testosterone levels 50,000 years ago correlates with the advent of modern culture and the complex communications of humans.

“Humans are uniquely able to communicate complex thoughts and cooperate even with strangers,” said Robert Cieri, University of Utah graduate biology student and lead author of the paper, in a statement. “New research on fossilized Stone Age humans from Europe, Africa and the Near East suggests these traits are linked, developed around 50,000 years ago, and were a driving force behind the development of complex culture.”

The researchers analyzed the bone structure of over 1,400 skulls of ancient and modern humans. Ancient humans exhibit bone structures that mimic bone structures of modern-day humans with high testosterone levels, such as a thick brow and sharp features. However, about 50,000 years ago, the skulls of humans began to display more feminine qualities and rounder features.

“Human fossils from after modern behavior became common have more feminine faces, and differences between the younger and older fossils are similar to those between faces of people with higher and lower testosterone levels living today,” said Cieri.

During ancient times, as higher population densities accumulated, there may have been an evolutionary advantage for lower testosterone. A lack of testosterone equals less aggressive behaviors from individuals, and could therefore spur cooperation and collaboration that previously could not have existed in a macho, testosterone-laden culture.

Scientists announced earlier this year that females are exposed to less testosterone in the womb, which leads to the so-called “female intuition,” which allows women to have a “more intuitive, less reflective” outlook of life.

“Whatever the cause, reduced testosterone levels enabled increasingly social people to better learn from and cooperate with each other, allowing the acceleration of cultural and technological innovation that is the hallmark of modern human success,” said Cieri.