In American folklore, testosterone is supposed to cause rage, lust, competitiveness, nuclear arms races, beer hats and other indicators of whacked-out excess masculinity. Andrew Sullivan, for example, wrote years ago about the "increased edginess and self-confidence'' that he got from hormone supplements--or, as he put it, his "biweekly encounter with a syringe full of manhood.'' He chased sex, he nearly got into fights, he bounced off the walls. Boo-yah!

If matters were that simple, then you'd expect that women who'd taken a testosterone dose before negotiating with each other would be more aggressive and reckless in their tactics.

Not so, says a report this week on the Nature website. Christoph Eisenegger and his colleagues had 121 women play the ultimatum game. Those who received testosterone beforehand were more fair and less egotistical than those who got a placebo.

Actually, there was one group of women who did behave according to stereotype, taking a much more "in-your-face'' stance in the talks. These were the women who thought they had been given testosterone.

Two conclusions: First, this is evidence for Eisenegger's more careful definition of testosterone's effect. He believes it's not a one-note promoter of aggression and lust, but rather a spur to competition for status. The experiment was designed to distinguish between the two theories: if testosterone just impels humans to act like rutting elks, then it should induce bad behavior at the bargaining table. But if it promotes status-seeking, then extra testosterone should make people want to win the game (with skillful, self-restraining effort) not burn down the casino. And that turned out to be what the study found.

More importantly, the work is a good reminder that we shouldn't assume that "bottom-up'' is a stronger explanation than "top-down'' for people's actions. Many tend to think that pills, hormones and brain scans are evidence of forces more real and powerful than ideas, feelings and conversation. That's a bias to watch out for. Testosterone isn't just a chemical; it's an idea about gender and behavior that many Americans have acquired. The chemical can cause behavior changes; so can the idea.

Henrich Caveat: The work was done on 121 young women in a rich nation. It's not definitive (I'm not aware of a lot of cross-cultural work on testosterone's effect). But in creating conditions where the "folk theory'' didn't work, it does dent the notion that testosterone could be "a syringe full of manhood.''