Pair-bonding
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Hover over keys for definitions:Mating systems are culturally-prescribed rules and conventions for who mates with whom, when, and how lasting and exclusive the nature of sexual relationships may be. There is no single universal human mating system, rather, substantial variability in patterns of reproductive practices and family systems are observed across cultures. Culturally-condoned mating systems span the range of variation from exclusive monogamy to polygyny, with rare instances of polyandry reported. Exclusive monogamy is rare in mammalian species and uncommon among primate species, and is not observed among great ape species. By contrast, monogamous pair-bonds are valued by some human cultures, wherein romantic love and sexual exclusivity are culturally reinforced.
Whereas primate groups generally follow species-specific patterns of mating behavior, human cultures show much greater variability between populations. In gorillas, for example, groups are defined as unimale, multi-female "harems" wherein a single male has sexual access to a range of females. In chimpanzees and bonobos, multiple males may mate with a female who is sexually receptive. Often, culturally-prescribed rules and conventions are in place to limit sexual access to females to a single male, who may couple monogamously or have multiple sexual and/or domestic partners. However, polyandry, wherein a female takes multiple partners, has been reported much more rarely. In one such example, women in Tibet and parts of India may take multiple husbands from a single family (fraternal polyandry) as a means of maintaining limited agricultural land within a single family.
Sophisticated rules for marriage often govern human reproduction, and reflect culturally-constructed ideas about the degree of relatedness individuals may have to each other. Incest taboos are common in human cultures, likely related to incest-avoidance mechanisms that exist in other species. However, sexual relationships between members of the same clan or moiety may be considered incestuous irrespective of individuals’ genetic relatedness.
In humans, the high metabolic demands associated with pregnancy and lactation make it very difficult for a mother to provide for her own and her offspring’s nutritional needs. Provisioning of a mother by the father of her offspring may be one way to help offset the demands of caring for a young child, contributing to higher rates of offspring survival, and thus, enhancing differential reproductive fitness. In humans, the interbirth interval (described as the length between the birth of offspring) is shorter on average, facilitated by the capacity to share responsibilities for caring for offspring with a partner or other members of a social group.
Bipedal locomotion may have served to free the hands of early hominids to carry food resources to group members, such as mothers, who cannot provide sufficient calories to meet their own nutritional needs, fostering greater provisioning of partners by males and encouraging paternal investment and monogamous mating systems. Monogamous relationships are predicted to occur more frequently in cultures where males provide contribute a higher proportion of calories to the local diet.
Patterns of mating systems may reflect certain ecological conditions. Among cultures where pathogen load is high, polygyny is especially common. Monogamy, by contrast, is more common in cultures where pathogen stress is low. Sex ratios may additionally favor the development of different mating strategies such that increased competition between males for reproductive access to females favors greater paternal investment in offspring. High mortality rates due to ecological factors may also have developmental effects contributing to learned attachment styles, such that uncertain offspring survivability corresponds to insecure attachment styles, recapitulated in more unrestricted sociosexuality in adult relationships. Alternately, variable seasonality and demanding environments may favor the emergence of biparental care to meet the demands of raising offspring in marginal areas.
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