Pair-bonded relationships are dyadic coalitions between sexual partners based on selective social attachments, often characterized by partner preference, biparental care and intrasexual aggression. Although it is debatable whether humans are truly monogamous lasting bonds between sexual partners are widespread throughout nearly all modern human societies. In humans pair-bonding probably evolved to increase paternal provisioning (1, 2) or as a consequence of male mating competition (3, 4). Furthermore, it has recently been suggested that pair-bonding behavior shaped the evolution of human society (5). Although pair-bonds are common in our species and an important part of human nature, knowledge about the biological foundations of the human propensity to engage in enduring pair-bonded relationships remain sparse.
