By Amarachi Orie, CNN(CNN) — Sexual behavior is one reason why female mammals typically live longer than their male counterparts, according to a new study. Among mammals, adult females lived 12% longer than males, the study found. Competing theoriesThere are several theories about why there are these sex differences in longevity. The scientists found evidence in support of the sexual selection theory, with female mammals living longer than males in species that were non-monogamous — having more than one sexual partner. Females with childcare responsibilities tended to live longer than males in zoos.