The urge to mate explains virtually everything that males do during the breeding season. They threaten, chase, and fight to establish rank in a dominance hierarchy that gives access to females. One or a few of the highest-ranking males dominate mating; the alpha male may inseminate up to 100 females in a single breeding season or more than 200 females in life. Variation in lifetime reproductive success is extreme. Most males never mate because they die before reaching breeding age or they mature, reach old age, and are prevented from mating by the power structure. Males attempt to mate with pregnant females, nursing females, females giving birth, dead females, and newly weaned pups. Females departing the harem after weaning their pups are weak, having lost 40% of their mass; they are in danger from peripheral males attempting to mate with them, and some are inadvertently killed.