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No, this isn’t some jab at dudes. According to a study published in Current Anthropology, our transition into modern civilization might have coincided with our species’ drop in testosterone.

The hormone, associated with both biologically male characteristics and aggression, makes skulls grow those heavy brows we associate with our evolutionary ancestors. Lead author Robert Cieri, a graduate student of biology at the University of Utah, said in a news release that a study of 1,400 modern and ancient skulls provided insight into how these changes might have overlapped with cultural shifts.

While the modern human — species Homo sapiens — appears in the fossil record around 200,000 years ago, evidence of the kind of “modernity” we associate with our species (like advanced tools and symbolic artifacts) took an additional 150,000 years to appear.

The key, the researchers claim, could be found in the feminized skulls that became more prevalent around that time. A rounder face in humans is associated with less testosterone, and less testosterone can mean better cooperation between individuals. Less head clubbing and more community building, basically.

One study isn’t quite enough to pin the origin of humanity on. But studying how humans and apes responded to evolutionary hormonal shifts can give us insights into the origins of culture and modernity.