In animal societies, control over resources and reproduction is often biased towards one sex. Such power asymmetries between the sexes largely shape male-female sexual and social relationships. In particular, males often coerce females in reproductive contexts, but also in other contexts. Yet, the ecological and evolutionary underpinnings of male-female power asymmetries remain poorly understood. In this talk, I use long-term data from wild primates as well as comparative data from the literature to show how variation in power asymmetries between the sexes can be quantified, and try to explain some of this variation.