Editing Animal sexual behaviour (section)

==Mating systems==
{{main|mating systems}}
In [[sociobiology]] and [[behavioural ecology]], the term [[mating system]] is used to describe the ways in which animal societies are structured in relation to sexual behaviour. The mating system specifies which males [[mate]] with which females, and under what circumstances. 

The following are some of the mating systems generally recognised in humans and other animals:
*[[Monogamy]]: One male and one female have an exclusive mating relationship. 
*[[Polygamy]]: One or more males have an exclusive relationship with one or more females. Three types are recognised: 
**[[Polygyny]] (the most common polygamous mating system in vertebrates so far studied): One male has an exclusive relationship with two or more females 
**[[Polyandry]]: One female has an exclusive relationship with two or more males.
**[[Polygynandry]]: Two or more males have an exclusive relationship with two or more females; the numbers of males and females need not be equal, and in vertebrate species studied so far, there are usually fewer males. 
*[[Promiscuity]]: Any male and female will mate within the social group. 

===Monogamy===
:''[[Portal:Main|Main]] article: [[Monogamamous pairing in animals]]''
Zoologists and biologists now have solid evidence that monogamous pairs of animals are not always sexually exclusive. Many animals that form pairs to mate and raise offspring regularly engage in sexual activities with extra-pair partners<ref name="Ågren,Zhou,Zhong,1989">Ågren, G., Zhou, Q. & Zhong, W. (1989). Ecology and social behaviour of Mongolian gerbils Meriones unguiculatus, at Xiliuhot, Inner Mongolia, China. Animal Behaviour, 37, 11-27.</ref><ref name="Barash,1981">Barash, D.P. (1981). Mate guarding and gallivanting by male hoary marmots (Marmota caligata). Behavioural Ecology and Sociobiology, 9, 187-193.</ref><ref name="Birkhead,Møller,1995">Birkhead, T.R. & Møller, A.P. (1995). Extra-pair copulations and extra-pair paternity in birds. Animal Behaviour, 49, 843-848.</ref><ref name="Birkhead,Møller,1996">Birkhead, T.R. & Møller, A.P. (1996). Monogamy and sperm competition in birds. In J. M. Black (Ed.), Partnerships in Birds: The Study of Monogamy (pp. 323-343). Oxford: Oxford University Press.</ref><ref name="Foltz,1981">Foltz, D.W. (1981). Genetic evidence for long-term monogamy in a small rodent, Peromyscus polionotus. American Naturalist, 117, 665-675.</ref><ref name="Gursky,2000">Gursky, S.L. (2000). Sociality in the spectral tarsier, Tarsius spectrum. American Journal of Primatology, 51, 89-101.</ref><ref name="Hasselquist,Sherman,2001"> Hasselquist, D. S. & Sherman, P.W. (2001). Social mating systems and extrapair fertilizations in passerine birds. Behavioural Ecology, 12, 457-466.</ref><ref name="Hubrecht,1985">Hubrecht, R.C. (1985). Home range size and use and territorial behaviour in the common marmoset, Callithrix jacchus jacchus, at the Tapacura Field Station, Recife, Brazil. International Journal of Primatology, 6, 533-550.</ref><ref name="Mason,1966">Mason, W.A. (1966). Social organization of the South American monkey, Callicebus moloch: a preliminary report. Tulane Studies in Zoology, 13, 23-28.</ref><ref name="McKinney,Derrickson,Mineau,1983">McKinney, F., Derrickson, S.R., & Mineau, P. (1983). Forced copulation in waterfowl. Behaviour, 86, 250-294.</ref><ref name=Reichard,1995">Reichard, U. (1995). Extra-pair Copulations in a Monogamous Gibbon (Hylobates lar). Ethology, 100, 99-112.</ref><ref name="Reichard,2002">Reichard, U.H. (2002). Monogamy—A variable relationship. Max Planck Research, 3, 62-67.</ref><ref name="Richardson,1987">Richardson, P.R.K. (1987). Aardwolf mating system: overt cuckoldry in an apparently monogamous mammal. South African Journal of Science, 83, 405-412.</ref><ref name="Welsh,Sedinger,1990"> Welsh, D. & Sedinger, J.S. (1990). Extra-Pair copulations in Black Brant. The Condor, 92, 242-244.</ref><ref name="Westneat,Stewart,2003>Westneat, D.F. & Stewart, I.R.K. (2003). Extra-pair paternity in birds: causes, correlates, and conflict. Annual Review of Ecology, Evolution, and Systematics, 34, 365-396.</ref> 
This includes previous exemplars such as [[swan]]s. Sometimes these extra-pair sexual activities lead to offspring. Genetic tests frequently show that some of the offspring raised by a monogamous pair come from the female mating with an extra-pair male partner.<ref name="Birkhead,Møller,1995"/><ref name="Birkhead,Møller,1996"/><ref name="Owens,Hartley,1998">Owens, I.P.F. & Hartley, I.R. (1998). Sexual dimorphism in birds: why are there so many different forms of dimorphism? Proceedings of the Royal Society, London, B265, 397–407.</ref><ref name="Solomon,Keane,Knoch,Hogan,2004">Solomon, N.G., Keane, B., Knoch, L.R., & Hogan, P.J. (2004). Multiple paternity in socially monogamous prairie voles (Microtus ochrogaster). Canadian Journal of Zoology, 82, 1667-1671.</ref>
These discoveries have led biologists to adopt new ways of talking about monogamy:
====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]].

===Polygamy===

Polygamy is defined as a mating structure in which a single individual of one gender has exclusive access to several individuals of the opposite gender.  It takes two main forms - polygyny and polyandry.  As polygyny is the most common form of polygamy among vertebrates (including humans, to some extent), it has been studied far more extensively than polyandry.

====Polygyny====
In some species, notably those with [[harem]] male structures, only one of a few males in a group of females will mate. This is also known as [[polygyny]] in [[sociobiology]].<ref>Technically, [[polygyny]] in sociobiology and zoology is defined as a system in which a male has a relationships with more than one female, but the females are predominantly bonded to a single male.</ref> Should the active male be driven out, killed, or otherwise removed from the group, in a number of species the new male will ensure that breeding resources are not wasted on another male's young.<ref>This section and examples taken from:[[Robert Sapolsky]] ''Why Zebras Don't get Ulcers'', p.140-141.</ref> The new male may achieve this in many different ways, including:
* Competitive [[infanticide (zoology)|infanticide]]
:in [[lion]]s and some [[monkey]]s the new male will kill other young; therefore, the females, which are no longer [[lactation|nursing]], rapidly become [[sexual receptiveness|receptive]] again.
* [[Harassment]] to [[miscarriage]]
:amongst wild [[horse]]s and [[baboon]]s, the male will "systematically harass" pregnant females until they miscarry.
* [[Pheromone]] based spontaneous abortion
:in some [[rodent]]s such as [[mouse|mice]], a new male with a different scent will cause females who are pregnant to spontaneously fail to implant recently fertilized eggs. This does not require contact; it is mediated by [[scent]] alone. It is known as the [[Bruce effect|Bruce-Parkes effect]].

===Promiscuity===
Two examples of systems in primates are [[promiscuous]] mating [[chimpanzees]] and [[bonobo]]s. These species live in social groups consisting of several males and several females. Each male copulates with many females, and vice versa. In bonobos, the amount of promiscuity is particularly striking because bonobos use sex to alleviate social conflict as well as to reproduce.

===Seasonal nature of animal sexuality===
Many animal species have specific mating (or breeding) seasons. These are often associated with changes to herd or group structure, and behavioural changes, including territorialism amongst individuals. These may be annual (eg wolves), biannual (eg dogs) or more frequently (eg horses). During these periods, females of most species are more mentally and physically [[receptive]] to sexual advances, a period often described as being "in season" or "in [[heat]]", but outside them animals still engage in sexual behaviours,<ref>For example, masturbation, trial mounting, and other behaviours are regularly seen in male animals out of season</ref> and such acts as do occur are not necessarily harmful.<ref name="danish">2006 Danish Animal Ethics Council report: "The mucous membrane in the female animal’s vagina and the animal’s behaviour is under influence of its rut cycle. That means that the animal is physically and mentally more ready for sexual activities at some times than at others. But this does not mean that sexual activity will lead to injuries, fear or suffering, if it happens outside the rut period."

(Danish: ''"Slimhinden i hundyrets vagina og dyrets adfærd er under indflydelse af dets brunstcyklus. Det betyder, at dyret er fysisk og mentalt mere parat til seksuelle aktiviteter på nogle tidspunkter end på andre. Men dette er ikke ensbetydende med, at den seksuelle aktivitet vil være forbundet med skader, angst og lidelse, hvis den foregår udenfor brunstperioden."'') [http://www.jm.dk/image.asp?page=image&objno=76595 Report November 2006 (PDF)]</ref>