Modern humans appear in the fossil record about 200,000 years ago, but it was only about 50,000 years ago that making art and advanced tools became widespread. A new study appearing Aug. 1 in the journal Current Anthropology finds that human skulls changed in ways that indicate a lowering of testosterone levels at around the same time that culture was blossoming.
“The modern human behaviors of technological innovation, making art and rapid cultural exchange probably came at the same time that we developed a more cooperative temperament,” said lead author Robert Cieri, a biology graduate student at the University of Utah who began this work as a senior at Duke University.
The study authors also suggest their theory explains differences between our closest ape relatives — aggressive chimpanzees and mellow, free-loving bonobos.
Those two apes develop differently, and they respond to social stress differently. Chimpanzee males experience a strong rise in testosterone during puberty, but bonobos do not. When stressed, the bonobos don’t produce more testosterone, as chimps do, but they do produce more cortisol, the stress hormone.
Their social interactions are profoundly different and, relevant to this finding, their faces are different, too. “It’s very hard to find a brow-ridge in a bonobo,”.