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In addition to fueling aggression, testosterone can also make men more generous, study says

In addition to fueling aggression, testosterone can also make men more generous, study says
Donald Trump, right, discusses his health on "The Dr. Oz Show." Trump, who recently revealed he has a testosterone level of 441 (generally above normal for a 70-year-old man), may be motivated by a hormonally-driven impulse to enhance his status, new research suggests. (Sony Pictures Entertainment / Associated Press)

Testosterone, the big daddy (if you will) of male hormones, has gotten a bit of a bad reputation, what with it being linked to bluster, aggression, violent offending and a whole raft of behaviors at which men do seem to best women consistently.

But in humans, new research suggests that's not the whole picture. The testosterone findings that have shaped our common assumptions probably fail to take account of human society's exquisite level of social evolution.

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We may routinely invoke testosterone to dismiss boorish behavior. But in polite society, the new research suggests, higher levels of testosterone also drive men to do good things: to donate to charities, behave gallantly toward those in need, and share the proceeds of business deals generously with cooperating business partners.

But here's the hitch: When driven by testosterone, those good deeds are anything but selfless, the research suggests. Testosterone's kind heart appears to be motivated by the same concerns as testosterone's better-established dark heart: a male's impulse to protect or enhance his status and thereby increase his chances of spreading his sperm far and wide.

In short, whether you're Andrew Carnegie, Bill Gates or Donald Trump, testosterone makes you loathe to accept a disrespectful business proposition and vindictive toward the person who dares propose it. But when a negotiating partner shows you the respect you believe is your due, testosterone may also be what drives you to respond generously.

Similarly, wrote the new paper's authors, among humans, public munificence  has come to enhance and consolidate a man's status in business and society. Under these evolved circumstances, a high level of testosterone might make a man an inveterate giver, even if his motivation — self-enhancement — is primitive.

In a study published Monday in the journal PNAS, researchers found that getting an extra shot of testosterone made men engage in seemingly contradictory behaviors. When an unseen negotiator lowballed male subjects plied with extra testosterone, their responses were unusually punishing, even when it cost subjects to inflict such punishment. But under the influence of extra testosterone, the same men responded to a negotiating partner's more respectful bid with outsized generosity.

The new research looked at the response of men between the ages of 18 and 30 to unseen negotiators ("proposers") in the "Ultimatum Game." In it, subjects ("responders") were asked to react to proposals to split a pot of money. If they accepted the share proposed, they got to keep that share. If they rejected the share proposed (say, because they perceived it to unfairly benefit the proposer), the pot of money went to neither side.

After playing the game, responders were then given the opportunity to reward or punish a proposer. Using some of his own earnings, a responder could either reduce the unseen negotiator's payout for playing or increase it by contributing a small share from his own pot.

When played by two people, the Ultimatum Game rewards cooperation and punishes undue greed for both players. When played by just a responder reacting to predetermined proposals, the Ultimatum Game is a good way to measure just how far a subject will go to punish another's greed or reward another's generosity.

When responders got an extra dose of testosterone, they were more likely than those who got a placebo to forfeit money by rejecting proposals that tilted heavily in favor of the proposer: their behavior suggested that they'd rather get no money than accept the proposal of a negotiator who did not respect them.

Compared to men who got a placebo, the men who got the testosterone shot were subsequently more vindictive toward proposers who proposed an unfair split, even when it cost them. But compared to those who got a placebo, the testosterone-enhanced men also chose bigger rewards for the proposers who had been fair with them.

Testosterone did not make men respond more quickly than those on placebo, so the authors of the new study concluded that testosterone didn't increase "emotional reactivity." Instead, testosterone "has a more restricted effect that is consistent with increasing status-enhancing aggressive and nonaggressive behaviors."

Follow me on Twitter @LATMelissaHealy and "like" Los Angeles Times Science & Health on Facebook.

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