Finally, an explanation for why bar bets sometimes escalate into bar fights: Levels of a “high-octane” form of testosterone soar when men think others don’t trust them.
Economist Paul Zak of Claremont Graduate University in California said scientists have known for years that aggressive behavior in animals is sparked by elevated testosterone–which is present in men and women, though women have significantly smaller amounts.
Less well understood is whether even mildly negative social interactions–such as feeling mistrusted by a stranger — can trigger testosterone surges. This is what Zak and his colleagues explored.
Zak’s research team gave $10 each to 106 men and 106 women (average age 22) to play a computerized “trust game” that allowed the subjects to keep any additional money (or absorb losses) from the decisions they make during the experiment.
The subjects were told they could choose to send any or all of their $10 (including none) to a randomly selected and anonymous partner. The amount of money they sent was then tripled in the receiving partner’s account; the receiver then could send back any amount (including nothing) to the sender. Thus the senders are giving away some of their stash, but they are hoping the receivers will react generously by sharing the tripled amount.
Zak’s team measured mistrust by how much money the receiver could have gotten from the sender but didn’t. Senders who sent $1 were labeled as less trusting than those who sent, say, $5. (The theory behind the trust experiments is that the original sender would pass along the entire $10, which would be tripled to $30 and added to the partner’s original $10. The receiver would split this $40. Thus each player would leave the game with $20, twice what they would have collected if the original sender, fearing he or she would get stiffed, kept the initial $10.)
After the players made their decisions, the researchers drew a blood sample from each and analyzed it. They found that men who received a high “distrust signal” from their partner (in the form of a smaller amount of money) exhibited increased levels of DHT, the biologically active metabolite of testosterone that circulates in both sexes. Women who received a strong distrust signal, however, showed no increase in DHT.
“This suggests that men in our experiment had an aggressive reaction when they received a signal of distrust, while women did not,” the researchers wrote in a recent issue of the American Economic Review.
While neither men nor women like being distrusted, “women don’t have the same physiological reaction as men do,” Zak says. “Women are just physiologically cooler.”
