Testosterone is associated with cooperation during intergroup competition by enhancing parochial altruism

Abstract

The steroid hormone testosterone is widely associated with negative behavioral effects, such as aggression or dominance. However, recent studies applying economic exchange tasks revealed conflicting results. While some point to a prosocial effect of testosterone by increasing altruistic behavior, others report that testosterone promotes antisocial tendencies. Taking into account additional factors such as parochial altruism (i.e., ingroup favoritism and outgroup hostility) might help to explain this contradiction. First evidence for a link between testosterone and parochial altruism comes from recently reported data of male soccer fans playing the ultimatum game. In this study high levels of endogenous testosterone predicted increased altruistic punishment during outgroup interactions and at the same time heightened ingroup generosity. Here, we report findings of another experimental task, the prisoner's dilemma, applied in the same context to examine the role of testosterone on parochial tendencies in terms of cooperation. In this task, 50 male soccer fans were asked to decide whether or not they wanted to cooperate with partners marked as either fans of the subject's own favorite team (ingroup) or fans of other teams (outgroups). Our results show that high testosterone levels were associated with increased ingroup cooperation during intergroup competition. In addition, subjects displaying a high degree of parochialism during intergroup competition had significantly higher levels of testosterone than subjects who did not differentiate much between the different groups. In sum, the present data demonstrate that the behavioral effects of testosterone are not limited to aggressive and selfish tendencies but may imply prosocial aspects depending on the context. By this means, our results support the previously reported findings on testosterone-dependent intergroup bias and indicate that this social hormone might be an important factor driving parochial altruism.

Keywords: altruistic behavior; competition; intergroup conflict; prisoner's dilemma; testosterone.

Figure 1

Experimental paradigm. Each trial started with a start frame informing the subject that now there will be a new interaction. Next, subjects saw a male silhouette representing the second player along with two small soccer team logos as well as the written name of the team to indicate the second player's favorite team. The first name and initial of the last name of the opponent was presented to increase plausibility of a real person. After this, subjects were asked to decide whether or not they would like to cooperate with the opposing player. They indicated their response via right or left button press. The second player's decision was then revealed along with feedback on the outcome according to the subject's decision.

Figure 2

Cooperation rates in the prisoner's dilemma. Cooperation rates decreased with increasing social distance to the opposing player's team. The group competition context further accentuated this parochial pattern resulting in increased cooperation rates with ingroup members whereas outgroup cooperation decreased (^*p < 0.01, ^**p < 0.001). Error bars indicate standard errors from mean (SEM).

Figure 3

Effect of testosterone on ingroup cooperation. High testosterone levels were associated with increased ingroup cooperation during the group competition relative to the neutral context (Δcontext: cooperation rates competition—neutral context).

Figure 4

Testosterone levels predict parochialism. Subjects displaying a higher tendency for parochial altruism during the competition (i.e., individuals who showed increased cooperation with the ingroup relative to the antagonistic outgroup) had significantly higher testosterone levels than subjects who did not show such a strong ingroup bias (^*p < 0.05). Error bars indicate standard errors of the mean (SEM).