In this study on sexuality across the menstrual cycle, a team of psychologists and biologists from the Georg August University Göttingen set out to study how women’s sexuality changes across the menstrual cycle. Unlike most primates, human exhibit few and subtle signs of increased sexual interest and activity, or ‘estrus’, around ovulation. For a long time, scientists have tried to understand this difference from an evolutionary perspective. Because these changes are so subtle, the team collected online diary data from more than one and a half thousand women over the course of seventy days. This unprecedented dataset will be used to test different theories about the impact of the human menstrual cycle on female sexuality and the effect of hormonal contraception on these cycles.