Digit ratios, the menstrual cycle and social preferences

We examine whether social preferences are partially determined by biological factors. We do this by investigating whether digit ratios (2D:4D) and menstrual cycle information are correlated with choices in trust, ultimatum, public good and dictator games. Digit ratios are thought to be a proxy for prenatal testosterone and oestrogen exposure and the menstrual cycle is a proxy for contemporary variations in a range of hormones. We find that digit ratios predict giving in all games. Giving in the trust, public good and dictator games as well as reciprocity in the trust game vary significantly over the menstrual cycle. We discuss possible mechanisms behind these effects and conclude that biological factors play an important role in shaping social preferences. ∗I am indebted to Hessel Oosterbeek and Erik Plug for their advice and support. I thank Burkhard Schipper and two anonymous referees for their many valuable comments. I would also like to thank seminar participants at the University of Amsterdam and at the ESA World Meeting 2010 for their comments. I also thank Lygia Cesar for great research assistance in the lab. I gratefully acknowledge financial support from the University of Amsterdam through the Speerpunt Behavioural Economics and thank CREED for letting me use their lab. University of Amsterdam, Roetersstraat 11, 1018 WB Amsterdam, The Netherlands; [email protected]; buser.economists.nl.