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August 03, 2010

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Poor, misunderstood testosterone

Dec. 8, 2009
Courtesy Nature
and World Science staff

De­spite pop­u­lar con­cep­tions about the hor­mone tes­tos­ter­one, in wom­en, at least, the sub­stance ac­tu­ally may pro­mote fair, con­cil­ia­to­ry be­hav­ior, re­search­ers say.

But the myths about tes­tos­ter­one are so pow­er­ful that wom­en in a study started act­ing less fairly if they thought they had re­ceived a dose of it, wheth­er they had or not.

Such are the find­ings of a study ap­pear­ing in the Dec. 8 ad­vance on­line is­sue of the re­search jour­nal Na­ture.

Test­os­terone is often called the “male” hor­mone and is po­pu­lar­ly asso­ciated with aggres­sion. Wom­en have some test­os­terone also, though.

Ernst Fehr of the Un­ivers­ity of Zu­rich, Switz­er­land, and col­leagues set up a bar­gain­ing game in which fe­male par­ti­ci­pants were giv­en a pill ei­ther of tes­tos­ter­one or of a neu­tral sub­stance, called a pla­ce­bo.

Those that re­ceived tes­tos­ter­one showed a “sub­stan­ti­al in­crease in fair bar­gain­ing be­haviour,” lead­ing to better so­cial in­ter­ac­tions, the re­search­ers wrote. But wom­en who thought that they re­ceived tes­tos­ter­one, wheth­er or not they ac­tu­ally did, “be­haved much more un­fair­ly” than those who thought that they re­ceived pla­ce­bo. 

So, the neg­a­tive, an­ti­so­cial con­nota­t­ion of in­creas­ing tes­tos­ter­one lev­els seems to be strong enough to in­duce neg­a­tive so­cial be­hav­iour even when the bi­o­log­i­cal re­sult is ac­tu­ally the op­po­site, the sci­en­tists re­marked.

Ev­i­dence from an­i­mal stud­ies does show that tes­tos­ter­one causes ag­gres­sion to­ward oth­er mem­bers of the spe­cies, Fehr and col­leagues wrote. Pop­u­lar wis­dom tends to as­sume hu­mans work the same way. But it has been un­clear wheth­er this is cor­rect. 

Stud­ies have in­deed found that male and fe­male pris­on­ers with vi­o­lent his­to­ries have high­er sal­i­vary tes­tos­ter­one lev­els than nonvi­o­lent pris­on­ers, the re­search­ers not­ed. But this does not show that the tes­tos­ter­one ac­tu­ally caused the vi­o­lence.

A com­pet­ing idea, they ob­served, is that tes­tos­ter­one mo­ti­vates peo­ple to seek high so­cial sta­tus. De­pend­ing on the situa­t­ion, they may try to achieve that ei­ther through vi­o­lence or through fair­ness.

In the con­text of the ex­pe­ri­men­tal bar­gain­ing game, fair­ness tended to help pro­tect so­cial sta­tus, ac­cord­ing to Fehr and col­leagues. 

In the “ul­ti­ma­tum game,” as it was called, two play­ers are pre­sented with a sum of mon­ey, which they can keep if they can agree on how to split it. The catch is that just one play­er gets to pro­pose—and only on­ce—how it should be di­vid­ed. The oth­er play­er must ac­cept or re­ject that of­fer. “Fair” of­fers, such as an even split, tend to be more readily ac­cepted than “un­fair” of­fers where the pro­pos­er tries to keep most of the mon­ey. Fehr and col­leagues sug­gested that tes­tos­ter­one mo­ti­vat­ed play­ers to pro­pose “fair­er” of­fers in or­der to avoid the so­cial af­front of re­jection.

* * *

Despite popular conceptions about the hormone testosterone, in women, at least, the substance actually may promote fair, conciliatory behavior, researchers say. But the myths about testosterone are so powerful that women in a study started acting less fairly if they thought they had received a dose of it, whether that was true or not. Such are the findings of a study to appear in the Dec. 8 advance online issue of the research journal Nature. Ernst Fehr of the University of Zurich, Switzerland, and colleagues set up a bargaining game in which female participants were either given a pill of testosterone or of a neutral substance, or placebo. Those that received testosterone showed a “substantial increase in fair bargaining behaviour,” reducing bargaining conflicts and improving social interactions, the researchers wrote. However, women who thought that they received testosterone, whether or not they actually did, “behaved much more unfairly” than those who thought that they received placebo. So, the negative, antisocial connotation of increasing testosterone levels seems to be strong enough to induce negative social behaviour even when the biological result is actually the opposite, the scientists remarked. Evidence from animal studies does show that testosterone causes aggression toward other members of the species, Fehr and colleagues wrote. Popular wisdom tends to assume humans work the same way. But it has been unclear whether this is correct. Studies have indeed found that male and female prisoners with violent histories have higher salivary testosterone levels than nonviolent prisoners, the researchers noted. But this does not show that the testosterone actually caused the violence. A competing idea, they observed, is that testosterone motivates people to seek high social status. Depending on the situation, they may try to achieve that either through violence or through fairness. In the context of the experimental bargaining game, fairness tended to help protect social status, according to Fehr and colleagues. In the “ultimatum game,” as it was called, two players are presented with a sum of money, which they can keep if they can agree on how to split it. The catch is that just one player gets to propose—and only once—how it should be divided. The other player must accept or reject that offer. “Fair” offers, such as an even split, tend to be more readily accepted than “unfair” offers where the proposing player tries to keep most of the money. Fehr and colleagues suggested that testosterone motivated players to propose “fairer” offers in order to avoid the social affront of rejection.