In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of offspring and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is frequently used in sociobiology and evolutionary biology circles. The term often implies either a lifelong socially monogamous relationship or a stage of mating interaction in socially monogamous species. It is sometimes used in reference to human relationships. Varieties According to evolutionary psychologists David P. Barash and Judith Lipton, from their 2001 book The Myth of Monogamy, there are several varieties of pair bonds: Short-term pair-bond: a transient mating or associations Long-term pair-bond: bonded for a significant portion of the life cycle of that pair Lifelong pair-bond: mated for life Social pair-bond: attachments for territorial or social reasons Clandestine pair-bond: quick extra-pair copulations Dynamic pair-bond: e.g. gibbon mating systems being analogous to "divorce" Human pair bonding Humans can experience all of the above-mentioned varieties of pair bonds. These bonds can be temporary or last a lifetime. Pair bonding is a behavioral and physiological bond between two mated individuals, and is rare among non-human primates. Humans also engage in social pair bonding, where two individuals will form a close relationship that does not involve sex. In humans and other vertebrates, pair bonds are created by a combination of social interaction and biological factors including neurotransmitters like oxytocin, vasopressin, and dopamine. Pair bonds are a biological phenomenon and are not equivalent to the human social institution of marriage. Married couples are not necessarily pair bonded. Marriage may be a consequence of pair bonding and vice versa. One of the functions of romantic love is pair bonding. Examples Birds Close to ninety percent of known avian species are monogamous, compared to five percent of known mammalian species. The majority of monogamous avians form long-term pair bonds which typically result in seasonal mating: these species breed with a single partner, raise their young, and then pair up with a new mate to repeat the cycle during the next season. Some avians such as swans, bald eagles, California condors, and the Atlantic Puffin are not only monogamous, but also form lifelong pair bonds. When discussing the social life of the bank swallow, Lipton and Barash state: For about four days immediately prior to egg-laying, when copulations lead to fertilization, the male bank swallow is