Azara’s Owl monkeys of South America are fully monogamous, with the father handling much of the child care. But indeed, these owl monkeys remain monogamous, published in march - this is the first genetic confirmation for any nonhuman primate. We are also unusual in the sense that fewer than even 10 percent of mammals form exclusive sexual relationships. Coupling up might have been the best move our ancestors ever made, an ancestral polygamous mating system was replaced by pairbonding when lower-ranked hominin males diverted energy from fighting one another toward finding food to bring females as an incentive to mate. These innovations, gave hominins, that tribe that emerged when early humans diverged from chimpanzees, a reproductive edge over apes. Keeping many mates is hard work. It involves a lot of fighting with other males and guarding females. Monogamy might have emerged as a way to reduce that effort. Without cooperative breeding, a social system in which alloparents help care for the young evolved among our ancient ancestors starting with H. erectus nearly two million years ago, early Homo would not have broken through the hypothetical “gray ceiling” that constrains an ape’s brain to a maximum volume of about 700 cubic centimeters.