Consciousness Blog 15 December 2009

According to a new study, reported in Nature, testosterone does not of itself induce aggression, but rather intensifies status-seeking behaviour in a human social setting.

Neuroscientist Christoph Eisenegger and economist Ernst Fehr, both of the University of Zurich, and economist Michael Naef of Royal Holloway in London tested a group of 120 female subjects in a game in which money could be won through the making of an acceptable offer for the distribution of a real amount of money. If no agreement was reached, neither party earned anything. Before the game the test subjects were administered either a dose of 0.5 mg testosterone or a corresponding placebo.

"If one were to believe the common opinion, we would expect subjects who received testosterone to adopt aggressive, egocentric, and risky strategies – regardless of the possibly negative consequences on the negotiation process," says Eisenegger. But the opposite was found: the subjects receiving testosterone generally made better, fairer offers than those who received placebos

"The preconception that testosterone only causes aggressive or egoistic behavior in humans is thus clearly refuted," says Eisenegger. "In the socially complex human environment, pro-social behavior secures status, and not aggression," says Michael Naef. "The interplay between testosterone and the socially differentiated environment of humans, and not testosterone itself, probably causes fair or aggressive behavior".

Testosterone of course existed long before humans came along, and like other chemical messengers in the brain had evolved to cause adaptive behaviour. Put simplistically, a bull moose is more likely to breed successfully if it aggressively challenges and defeats its male fellows, whereas in the sophisticated human social group, females make their choices in a more nuanced fashion. Successful males, such as prime ministers, billionaires, film stars and top golfers have no difficulty in finding females. And their success is based not on brute strength or aggression, but an understanding in depth of how to succeed in the game of life, which means to be a leader or prime mover in the group.

Just one more example of how evolution took advantage of a pre-existing feature of the human brain during its adaptation to the new, groupish environment.

Read more in Chapter Three of Agent Human by Michael Bell.


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