A Double-Edged Hormone

Popularly associated with blunt male aggression, testosterone may in fact operate more like the titular boss in The Godfather—inducing us to reward people who toe the line and to lash out at those who cross it.

A study by researchers at Dublin's Trinity College and St. James's Hospital provides a fresh look at the hormone's social sway. Forty men were injected with either testosterone or a placebo and took part in several rounds of an experimental game. Each received an offer from another player to split a sum of money, and he could either accept the terms or reject the money altogether (if, for example, he felt his share was too small). After each exchange, the participant was given the power to respond to the other player's kindness (or lack thereof) with a bonus or a fine.

Compared with the placebo group, the men who received testosterone were more likely to inflict financial punishment on players who had made unfair offers, but they were also more likely to reward players who had made generous proposals. These results help flesh out the idea, first posited decades ago, that testosterone might serve less to boost aggression than to encourage status-enhancement. "In a lot of nonhuman animal species, that's done through aggressive means, but humans have more nuanced and complex ways of determining status," says Pranjal Mehta, a psychologist at the University of Oregon.

Reacting aggressively to perceived slights may raise your profile, but so can showing others that you are fair-minded. In a 2013 study with female participants, Mehta and colleagues found that a dose of testosterone predicted greater reciprocation of trust. Other researchers have reported evidence that men treated with testosterone are less likely to lie. Larger studies are needed, but these experiments suggest that the influence of the hormone on a person's actions may hinge on the demands of the social environment.

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