According to a group of anthropologists headed by Dr Brian Hare of Duke University, a decline in testosterone levels about 50,000 years ago led to the development of advanced tools and art.
There are a lot of theories about why, after 150,000 years of existence, humans suddenly leapt forward in technology.
Around 50,000 years ago, there is widespread evidence of producing bone and antler tools, heat-treated and flaked flint, projectile weapons, grindstones, fishing and birding equipment and a command of fire.
“Was this driven by a brain mutation, cooked foods, the advent of language or just population density?”
Dr Hare and his colleagues argue that human society advanced when people started being nicer to each other, which entails having a little less testosterone in action.
“If prehistoric people began living closer together and passing down new technologies, they’d have to be tolerant of each other. The key to our success is the ability to cooperate and get along and learn from one another,” said Robert Cieri, a student at the University of Utah and the first author on the study published in the journal Current Anthropology.
In their study, the scientists compared the brow ridge, facial shape and interior volume of 13 modern human skulls older than 80,000 years, 41 skulls from 10,000 to 38,000 years ago, and a global sample of 1,367 20th century skulls from 30 different ethnic populations.
The trend that emerged was toward a reduction in the brow ridge and a shortening of the upper face, traits which generally reflect a reduction in the action of testosterone.
“Heavy brows were out, rounder heads were in, and those changes can be traced directly to testosterone levels acting on the skeleton,” said Prof Steven Churchill of Duke University, a co-author on the study.
What the anthropologists can’t tell from the bones is whether these humans had less testosterone in circulation, or fewer receptors for the hormone.
Robert L. Cieri et al. 2014. Craniofacial Feminization, Social Tolerance, and the Origins of Behavioral Modernity. Current Anthropology, vol. 55, no. 4, pp. 419-443; doi: 10.1086/677209