Eisenegger et al. reply

Replying to J. van Honk, E. R. Montoya, P. A. Bos, M. van Vugt & D. Terburg Nature 485 10.1038/nature11136 (2012) van Honk and colleagues have taken our findings on the role of testosterone in ultimatum game bargaining1 a step forward by showing that the hormone has important prosocial effects beyond the ultimatum game by increasing cooperation in the public goods game (PGG)2. In contrast to the ultimatum game, participants in the PGG decide simultaneously about their cooperation levels and are not confronted with a rejection threat from other participants, suggesting a much more universal effect of testosterone on prosociality than revealed by our study1. As the PGG captures a large class of evolutionarily and contemporaneously important situations, their findings are of great interest, and considerably extend our knowledge about the causal effect of testosterone on social behaviour. In addition, their results raise intriguing questions regarding the motivational and biological mechanisms through which testosterone increased cooperation levels, suggesting that the study will trigger further important experiments.