Did Reduced Testosterone Levels Help Human Culture Advance?

August 3, 2014

Image Caption: A composite image shows the facial differences between an ancient modern human with heavy brows and a large upper face and the more recent modern human who has rounder features and a much less prominent brow. The prominence of these features can be directly traced to the influence of the hormone testosterone. Credit: Robert Cieri, University of Utah

redOrbit Staff & Wire Reports Your Universe Online

Changes in the human skull occurring approximately 50,000 years ago indicate that the rise of culture occurred around the same time as a reduction in testosterone levels, according to new research appearing in the August 1 edition of the journal Current Anthropology.

In the study, lead author Robert Cieri, a biology graduate student at the University of Utah who began this work as a senior at Duke University, argue that people started making art and using advanced tools only after they became nicer to each other. Those gentler personalities required having slightly reduced testosterone levels, they added a condition suggested by the more feminine features found in skulls recovered from that era.

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, Cieri explained in a statement Friday.

The research team based their theory on measurements of over 1,400 ancient and modern skulls. Their efforts revealed that more recent modern humans had rounder features and a much less prominent brow, and those changes can be traced back directly to the impact of testosterone levels on the skeleton.

They are not certain if the bones indicate that these individuals had less testosterone in circulation, or fewer receptors for the hormone. However, fellow investigators and Duke university animal cognition researchers Brian Hare and Jingzhi Tan state that this hypothesis is in line with what has previously been established in non-human species.

For example, selective breeding of Siberian foxes was eventually able to produce creatures that were less aggressive towards humans and were more juvenile in appearance and behavior after several generations. Hare said that observing a process that leads to these types of changes in other creatures might also explain human behavior.

It might help explain who we are and how we got to be this way, said Hare, who researches differences between humans and their closes ape relatives, the more aggressive chimpanzees and the more laid-back bonobos. Those apes develop differently, he said, and they respond to social stress in different ways.

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Did Reduced Testosterone Levels Help Human Culture Advance?

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