Digit ratios, the menstrual cycle and social preferences

► We correlate 2D:4D and menstrual cycle measures with choices in trust, ultimatum, public good and dictator games. ► 2D:4D is a marker for prenatal hormone exposure and menstrual cycle is a proxy for contemporary biological processes. ► Subjects with lower 2D:4D are less generous in all games. ► Giving in the trust and public good games and reciprocity in the trust game vary over menstrual cycle. ► Social preferences are shaped by prenatal and current biological factors.