Editing Mating system (section)

===In humans===
{{See also|Monogamy|Polygyny|Polyandry|Polyamory}}
Compared to other [[vertebrate]]s, where a species usually has a single mating system, humans display great variety. Humans also differ by having formal [[marriage]]s, which in some cultures involve negotiation and arrangement between elder relatives. Regarding sexual dimorphism (see the section about animals above), humans are in the intermediate group with moderate sex differences in body size but with relatively small testes,<ref name="Dixson 2018">{{cite journal |last1=Dixson |first1=Alan |title=Copulatory and Postcopulatory Sexual Selection in Primates |journal=Folia Primatologica |date=May 2018 |volume=89 |issue=3–4 |pages=258–286 |doi=10.1159/000488105 |url=https://karger.com/fpr/article/89/3-4/258/144087/Copulatory-and-Postcopulatory-Sexual-Selection-in |access-date=31 July 2023|doi-access=free |pmid=29804108 }}</ref> indicating relatively low sperm competition in socially monogamous and polygynous human societies. One estimate is that 83% of human societies are polygynous, 0.05% are polyandrous, and the rest are monogamous. Even the last group may at least in part be genetically polygynous.<ref name=Oxford2007>The Oxford Handbook of Evolutionary Psychology, Edited by Robin Dunbar and Louise Barret, Oxford University Press, 2007, Chapter 30 Ecological and socio-cultural impacts on mating and marriage systems by Bobbi S. Low</ref>

From an evolutionary standpoint, females are more prone to practice [[monogamy]] because their reproductive success is based on the resources they are able to acquire through reproduction rather than the quantity of offspring they produce. However, males are more likely to practice [[polygamy]] because their reproductive success is based on the amount of offspring they produce, rather than any kind of benefit from parental investment.<ref name="Cartwright 2002 19">{{Cite book|title=Evolutionary Explanations of Human Behaviour|last=Cartwright|first=John. H|publisher=Taylor and Francis e-Library|year=2002|isbn=978-0-203-47064-0|location=New York, NY|pages=19}}</ref>

Polygyny is associated with an increased sharing of subsistence provided by women. This is consistent with the theory that if women raise the children alone, men can concentrate on the mating effort. Polygyny is also associated with greater environmental variability in the form of variability of [[rainfall]]. This may increase the differences in the resources available to men. An important association is that polygyny is associated with a higher [[pathogen]] load in an area which may make having good genes in a male increasingly important. A high pathogen load also decreases the relative importance of [[sororal polygyny]] which may be because it becomes increasingly important to have genetic variability in the offspring (See [[Major histocompatibility complex and sexual selection]]).<ref name=Oxford2007/>

Virtually all the terms used to describe animal mating systems were adopted from [[social anthropology]], where they had been devised to describe systems of [[marriage]]. This shows that human sexual behavior is unusually flexible since, in most animal species, one mating system dominates. While there are close analogies between animal mating systems and human marriage institutions, these analogies should not be pressed too far, because in human societies, marriages typically have to be recognized by the entire social group in some way, and there is no equivalent process in animal societies. The temptation to draw conclusions about what is "natural" for human sexual behavior from observations of animal mating systems should be resisted: a socio-biologist observing the kinds of behavior shown by humans in any other species would conclude that all known mating systems were natural for that species, depending on the circumstances or on individual differences.<ref name="Cartwright 2002 19"/>

As culture increasingly affects human mating choices, ascertaining what is the 'natural' mating system of the human animal from a zoological perspective becomes increasingly difficult. Some clues can be taken from human anatomy, which is essentially unchanged from the prehistoric past:

*humans have a small relative size of testes to body mass in comparison to most primates;<ref name="Dixson 2018" />
*humans have a small ejaculate volume and sperm count in comparison to other primates;<ref name="Dixson 2018"/><ref name="Gerhard 2013">{{cite journal |last1=Van der Horst |first1=Gerhard |last2=Maree |first2=Liana |title=Sperm form and function in the absence of sperm competition |journal=Molecular Reproduction and Development |date=November 2013 |volume=81 |issue=3 |pages=204–216 |doi=10.1002/mrd.22277 |pmid=24273026 |s2cid=43821455 |url=https://onlinelibrary.wiley.com/doi/full/10.1002/mrd.22277 |access-date=31 July 2023|url-access=subscription }}</ref>
*as compared to most primates, humans spend more time in copulation;
*as compared to most primates, humans [[human reproduction#Copulation|copulate]] with lower frequency;<ref name="Dixson 2018" />
*the outward signs of [[Estrous cycle|estrus]] in women (i.e. higher body temperature, breast swelling, sugar cravings, etc.), are often perceived to be less obvious in comparison to the outward signs of ovulation in most other mammals;
*for most mammals, the estrous cycle and its outward signs bring on mating activity; the majority of female-initiated matings in humans coincides with estrus,<ref>{{cite journal|last1=Beach|first1=Frank|title=Sexual attractivity, proceptivity, and receptivity in female mammals|journal=Hormones and Behavior|date=1976|volume=7|issue=1|pages=105–138|doi=10.1016/0018-506x(76)90008-8|pmid=819345|s2cid=5469783}}</ref> but humans copulate throughout the reproductive cycle;
*after ejaculation/orgasm in males and females, humans release a hormone that has a sedative effect;<ref>{{cite journal|last1=Esch|first1=Tobias|last2=Stefano|first2=George|title=The Neurobiology of Love|journal=Neuro Endocrinology Letters|date=June 2005|volume=26|issue=3|pages=175–92|pmid=15990719}}</ref>

Some have suggested that these anatomical factors signify some degree of [[Human sperm competition|sperm competition]], although others have provided anatomical evidence to suggest that sperm competition risk in humans is low;<ref name="Dixson 2018" /><ref name="Gerhard 2013" />
*humans have a small ejaculate volume and sperm count in comparison to other primates,<ref name="Dixson 2018" /><ref name="Gerhard 2013" /> even though levels of genetic and societal promiscuity are highly varied across cultures,<ref>{{cite journal |first=Frank W. |last=Marlowe |date=August 2003 |title=The Mating System of Foragers in the Standard Cross-Cultural Sample |journal=Cross-Cultural Research |volume=37 |issue=3 |url=http://raptor1.bizlab.mtsu.edu/s-drive/TEFF/662/papers2010/men_dominance/The%20Mating%20System%20of%20Foragers%20in%20the%20Standard%20Cross-Cultural%20Sample.pdf |access-date=2014-02-26 |pages=282–306 |doi=10.1177/1069397103254008 |s2cid=145482562 |url-status=dead |archive-url=https://web.archive.org/web/20140302125838/http://raptor1.bizlab.mtsu.edu/s-drive/TEFF/662/papers2010/men_dominance/The%20Mating%20System%20of%20Foragers%20in%20the%20Standard%20Cross-Cultural%20Sample.pdf |archive-date=2014-03-02}}</ref>