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 ultimatum, trust, 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. In our preferred specification, giving in the trust and public good games as well as reciprocity in the trust and ultimatum games 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.