Some anthropologists now believe that advanced human behaviors like toolmaking only developed when early humans evolved to have lower levels of testosterone than their ancestors, according to a new study published in Current Anthropology.
"All of a sudden, in the archeological record, culture and advanced technology suddenly becomes more widespread. And at that time we also see a decrease in testosterone," said the study's lead author Bob Cieri, a graduate student at the University of Utah. "Before 50,00 years ago, there were brief flashes of advanced behavior and artifacts, but they're not persistent and widespread."
Cieri measured the browridge of different human skulls, which indicates the level of testosterone in the skeleton. Heavier brows and longer faces indicate more testosterone, and more rounded heads indicate less testosterone, according to Stephen Churchill, the Duke professor who supervised Cieri's work. Cieri measured 13 human skulls that were more than 80,000 years old; 41 skulls between 10,000 and 38,000 years old; and over 1,200 20th-century skulls from different ethnic populations. He found that the modern skulls had substantially more rounded features and less heavy brows than the early skulls, indicating a drop in testosterone between our early ancestors and modern humans.
Cieri says the decrease in testosterone levels could be attributed to the rise in the Homo sapiens population, which meant that people had to be nicer to each other because they were living in closer quarters. "If population density starts increasing, not only are there more people in your immediate environment that you have to get along with, but all land would be occupied with human groups," he explains. "You wouldn't just go across to the other side of the valley to hunt bison by yourself, you'd go to the other side of the valley and maybe make a treaty with the other people who live there."
It's important to note that these early humans didn't yet have "culture" as we know it — they were still hunter-gatherers, Cieri says, but they were much less aggressive about it. But he thinks this lowering of testosterone led to more cooperation between people, which laid crucial groundwork for cultural advances thousands of years later.
So if you're still worried about low T after reading TIME's recent cover story, "Manopause?!," consider that a little less T isn't always a bad thing.