Editing Animal sexual behaviour (section)

====Social monogamy====

{{quote|Social monogamy refers to a male and female's social living arrangement (e.g., shared use of a territory, behaviour indicative of a social pair, and/or proximity between a male and female) without inferring any sexual interactions or reproductive patterns. In humans, social monogamy equals monogamous marriage. Sexual monogamy is defined as an exclusive sexual relationship between a female and a male based on observations of sexual interactions. Finally, the term genetic monogamy is used when DNA analyses can confirm that a female-male pair reproduce exclusively with each other. A combination of terms indicates examples where levels of relationships coincide, e.g., sociosexual and sociogenetic monogamy describe corresponding social and sexual, and social and genetic monogamous relationships, respectively.|Reichard, 2003, page 4<ref>Reichard, U.H. (2003). Monogamy: Past and present. In U.H. Reichard and C. Boesch (Eds.), Monogamy: Mating strategies and parnternships in birds, humans, and other mammals (pp.3-25).Cambridge: Cambridge University Press.</ref>}}

Whatever makes a pair of animals socially monogamous does not necessarily make them sexually or genetically monogamous. Social monogamy, sexual monogamy, and genetic monogamy can occur in different combinations.

Social monogamy is relatively rare in the animal kingdom. The actual incidence of social monogamy varies greatly across different branches of the evolutionary tree. Over 90 percent of avian species are socially monogamous.<ref name="Reichard,2002" /><ref name="Barash,Lipton,2001">Barash, D.P. & Lipton, J.E. (2001). The Myth of Monogamy. New York, NY: W.H. Freeman and Company.</ref>

This stands in contrast to mammals. Only 3 percent of mammalian species are socially monogamous, although up to 15 percent of primate species are socially monogamous.<ref name="Reichard,2002" /><ref name="Barash,Lipton,2001" /> Social monogamy has also been observed in reptiles, fish, and insects. 

Sexual monogamy is very rare among animals. The great majority of socially monogamous species engage in [[extra-pair copulations]], making them sexually non-monogamous. For example, while over 90% of birds are socially monogamous, "on average, 30 percent or more of the baby birds in any nest [are] sired by someone other than the resident male."<ref name="NY Times Mating">[http://query.nytimes.com/gst/fullpage.html?res=9C0CEFDC143FF932A1575BC0A966958260 Mating for Life? It's Not for the Birds of the Bees - New York Times<!-- Bot generated title -->]</ref>
[[Patricia Adair Gowaty]] has estimated that, out of 180 different species of socially monogomous songbirds, only 10 percent are sexually monogamous.<ref name="Gowaty,Morell,1998">Research conducted by Patricia Adair Gowaty. Reported by Morell, V. (1998). Evolution of sex: A new look at monogamy. Science, 281, 1982-1983.</ref>

The incidence of genetic monogamy, determined by DNA fingerprinting, varies widely across species. For a few rare species, the incidence of genetic monogamy is 100 percent, with all offspring genetically related to the socially monogamous pair. But genetic monogamy is strikingly low in other species. Barash and Lipton note:

{{quote|The highest known frequency of extra-pair copulations are found among the fairy-wrens, lovely tropical creatures technically known as ''Malurus splendens'' and ''Malurus cyaneus''. More than 65 percent of all fairy-wren chicks are fathered by males outside the supposed breeding group.|Barash & Lipton, 2001, page 12<ref name="Barash,Lipton,2001" />}}

Such low levels of genetic monogamy have surprised biologists and zoologists, forcing them to rethink the role of social monogamy in evolution. They can no longer assume social monogamy determines how genes are distributed in a species. The lower the rates of genetic monogamy among socially monogamous pairs, the less of a role social monogamy plays in determining how genes are distributed among offspring. See also [[Evolution of Monogamy]].