Northern gannet pair
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.
Monogamous voles (such as prairie voles) have significantly greater density and distribution of vasopressin
receptors in their brain when compared to polygamous voles. These
differences are located in the ventral forebrain and the
dopamine-mediated reward pathway.
Peptide arginine vasopressin (AVP), dopamine, and oxytocin
act in this region to coordinate rewarding activities such as mating,
and regulate selective affiliation. These species-specific differences
have shown to correlate with social behaviors, and in monogamous prairie
voles are important for facilitation of pair bonding. When compared to montane voles, which are polygamous, monogamous prairie voles appear to have more of these AVP and oxytocin neurotransmitter receptors. It is important that these receptors are in the reward centers of the brain because that could lead to a conditioned
partner in the prairie vole compared to the montane vole which would
explain why the prairie vole forms pair bonds and the montane vole does
not.
Varieties
Black-backed jackals are one of very few monogamous
mammals. This pair works together in teamwork to hunt down prey and
scavenge. They will stay together until one of the two dies.
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, as in cuckold situations
- Clandestine pair-bond: quick extra-pair copulations
- Dynamic pair-bond: e.g. gibbon mating systems being analogous to "swingers"
Humans and pair bonding
Pair-bonded human male and female
Humans can experience some or all of the above-mentioned varieties of
pair bonds in their lifetime. These bonds can be temporary or last a
lifetime, same age or with different age groups. In a biological sense
there are two main types of pair bonds exhibited in humans: social pair bonding and sexual
pair bonding. The social pair bond is a strong behavioral and
psychological relationship between two individuals that is measurably
different in physiological and emotional terms from general friendships or other acquaintance relationships.
On the other hand, the sexual pair bond is a behavioral and
physiological bond between two individuals with a strong sexual
attraction component. In this bond the participants in the sexual pair
bond prefer to have sex with each other over other options. Social pair
bonds are usually more wide-ranging than their sexual counterparts due
to the sexual nature involved in the latter. In humans and other mammals, these pair bonds are created by a combination of social interaction and biological factors including neurotransmitters like oxytocin, vasopressin, and dopamine.
Pair bonds (social and/or sexual) are a biological phenomenon and are not equivalent to the human social institution of marriage.
Marriage can be associated with a sexual or social pair bond; however,
married couples do not necessarily have to experience both or either of
these bonds. Marriage can be a consequence of pair bonding and vice
versa; however, neither always creates or leads to the other. Pair
bonding in humans helps explain extreme "bonds" that we may share with others but are unable to articulate in terms of contemporary "love".
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 fertilizations, the male bank swallow is very busy, attentively guarding his female. Before this time, as well as after—that is, when her eggs are not ripe, and again after his genes are safely tucked away inside the shells—he goes seeking extra-pair copulations with the mates of other males…who, of course, are busy with defensive mate-guarding of their own.
Male (left) and female (right) mallard ducks form seasonal monogamous pairs.
In various species, males provide parental care and females mate with
multiple males. For example, recent studies show that extra-pair
copulation frequently occurs in monogamous birds in which a "social"
father provides intensive care for its "social" offspring.
Fishes
A University of Florida scientist reports that male sand gobies
work harder at building nests and taking care of eggs when females are
present – the first time such “courtship parental care” has been
documented in any species.
In the cichlid species Tropheus moorii, a male and female will form a temporary monogamous pair bond and spawn; after which, the female leaves to mouthbrood the eggs on her own. T. moorii broods exhibit genetic monogamy (all eggs in a brood are fertilized by a single male). Another mouth brooding cichlid - the Lake Tanganyika cichlid (Xenotilapia rotundiventralis) has been shown that mating pairs maintain pair bonds at least until the shift of young from female to male. More recently the Australian Murray cod has been seen maintaining pair bonds over 3 years
Mammals
As
noted above, different species of voles vary in their sexual behavior,
and these differences correlate with expression levels of vasopressin
receptors in reward areas of the brain. Scientists were able to change
adult male montane voles' behavior to resemble that of monogamous
prairie voles in experiments in which vasopressin receptors were
introduced into the brain of male montane voles.
