International audienceAnimal reproductive phenology varies from strongly seasonal to non-seasonal, sometimes among closely related or sympatric species. While the extent of reproductive seasonality is often attributed to environmental seasonality, this fails to explain many cases of non-seasonal breeding in seasonal environments. We investigated the evolutionary determinants of nonseasonal breeding in a wild primate, the chacma baboon (Papio ursinus), living in a seasonal environment with high climatic unpredictability. We tested three hypotheses proposing that non-seasonal breeding has evolved in response to (1) climatic unpredictability, (2) reproductive competition between females favoring birth asynchrony, and (3) individual, rank-depen...