It is present in many animal species and can sometimes be expressed in lieu of parental care by males. Mate guarding is a typical tactic in monogamous species. Female voles have shown no difference in fecundity with genetic monogamy, but it may be enforced by males in some instances. In some species, genetic monogamy has been enforced. Though individual pairs may be genetically monogamous, no one species has been identified as fully genetically monogamous. Genetic monogamy refers to a mating system in which fidelity of the bonding pair is exhibited. The proposed conflict is derived from the conflict-centric differential allocation hypothesis, which states that there is a tradeoff between investment and attractiveness. Sexual conflicts that have been proposed to arise from social monogamy include infidelity and parental investment. In largemouth bass, females are sometimes seen to exhibit cuckold behavior by laying some of their eggs in another female's nest, thus 'stealing' fertilizations from other females. This could be because of the shared energy expenditure by the males and females lower each individual's input.

It has been shown that female prairie voles live longer when paired with males in a social monogamous relationship. Social monogamy has been shown to increase fitness in prairie voles. The existence of purely social monogamy is a polygamous or polyandrous social pair with extra pair coupling. With social monogamy there may not be an expected sexual fidelity between the males and the females. Paternal care in monogamous species is commonly displayed through carrying, feeding, defending, and socializing offspring. The two individuals may cooperate in search of resources such as food and shelter and/or in caring for young. Social monogamy refers to the cohabitation of one male and one female. Monogamy is quite rare in fish and amphibians, but not unheard of, appearing in a select few species. A larger percentage of avian species are known to have monogamous relationships (about 90%), but most avian species practice social but not genetic monogamy in contrast to what was previously assumed by researchers. Monogamy in mammals is rather rare, only occurring in 3–9% of these species. As an example, in the cichlid species Variabilichromis moorii, a monogamous pair will care for eggs and young together, but the eggs may not all be fertilized by the male giving the care. Monogamy can be partitioned into two categories, social monogamy and genetic monogamy which may occur together in some combination, or completely independently of one another. Monogamy may either be short-term, lasting one to a few seasons or long-term, lasting many seasons and in extreme cases, life-long. This pair may cohabitate in an area or territory for some duration of time, and in some cases may copulate and reproduce with only each other. Monogamy is defined as a pair bond between two adult animals of the same species – typically of the opposite sex.

6 Mate assistance and territory defense.

Monogamy vs serial monogamy vs polygamy