Models to explain life history variation distinguish somatic from reproductive effort – the former including allocation to growth, maintenance, and repair, while the latter is effort directly devoted to producing descendants. Two distinct kinds of reproductive effort, parenting and mating, have been distinguished based on Darwin’s theory of sexual selection to explain the evolution of features, usually found in males, that reduce the survival prospects of their carriers but increase their success in mating competition. While Darwin did not explicitly identify the difference in gamete size, or potential reproductive rates, between the sexes as the basis for the fact that male paternity competition is a zero-sum game, he recognized the consequences of this difference for sexually reproducing species. Features could improve success in mating competition either by directly enhancing success in competition for mates, the “armaments” of male-male competition, or by increasing the likelihood of being chosen as a mate by members of the opposite sex, the “ornaments” that evolve through female choice. Mating competition among males plays an important role in favoring larger size in primate males. Male mating competition underlies the threat of male infanticide that occurs widely in the primate order, favoring both male and female counter-strategies, and probably explaining the unusual sociality of primates. The larger size of adult males, a characteristic of all the great apes including humans, is generally attributed to size advantages in male-male competition. In addition to size differences, many features of male physiology and emotional architecture may be a legacy of advantages in male-male mating competition. Long favored scenarios to explain human evolution emphasize the importance of male parental effort in the human lineage, assuming a large difference on this score between humans and the other great apes where male reproductive effort is almost entirely directed to mating competition. But in recent decades observations of hunter-gatherer foraging and food sharing strategies have often found that men specialize in foods that come in large packages, are risky to acquire, and then claimed so widely that the hunter’s own wife and children get no special share. Payoffs to the hunters themselves appear to come through improving their standing relative to other men, status advantages that may give mating rather than parenting benefits.