Stable mating relationships are widespread in our species, with important economic, social, and reproductive implications.' Pair-bonds are part of the unique human mosaic, including very large brains, childhood, concealed ovulation, sexual intercourse in private, cultural symbols, and complex social groups. Yet we understand relatively little about the evolution of human pairing, its functions, and consequences for human diversity. We can define pair-bonds as the long-term affiliation, including a sexual relationship, between two individuals. The important point is that the union, whether monogamous or polygamous, is relatively enduring. Recent debate about human pair-bonds highlights apparently conflicting hypotheses: Are pair-bonds the evolutionary consequence of male mating competition(2,3) or are they an adaptation for paternal provisioning ?(4,5) Unfortunately, a simple answer seems unlikely. The evidence indicates selective pressures from both mating competition and provisioning needs, suggesting different benefits of pair-bonds in different contexts. Whether a bond emphasizes mating or parenting effort may depend on environmental cues. Childhood experience evidently affects pair-bond development, suggesting further adaptive design for flexible life-history strategies.
