Editing Mating system (section)

===Genetic causes and effects===
Monogamy has evolved multiple times in animals, with [[Homology (biology)|homologous]] brain structures predicting the mating and parental strategies used by them. These homologous structures were brought about by similar mechanisms. Even though there have been many different evolutionary pathways to get to monogamy, all the studied organisms express their genes very similarly in the fore and midbrain, implying a universal mechanism for the evolution of monogamy in vertebrates.<ref name="Young et al 2019">{{cite journal |last1=Young |first1=Rebecca L. |last2=Ferkin |first2=Michael H. |last3=Ockendon-Powell |first3=Nina F. |last4=Orr |first4=Veronica N. |last5=Phelps |first5=Steven M. |last6=Pogány |first6=Ákos |last7=Richards-Zawacki |first7=Corinne L. |last8=Summers |first8=Kyle |last9=Székely |first9=Tamás |last10=Trainor |first10=Brian C. |last11=Urrutia |first11=Araxi O. |last12=Zachar |first12=Gergely |last13=O’Connell |first13=Lauren A. |last14=Hofmann |first14=Hans A. |title=Conserved transcriptomic profiles underpin monogamy across vertebrates |journal=Proceedings of the National Academy of Sciences |date=22 January 2019 |volume=116 |issue=4 |pages=1331–1336 |doi=10.1073/pnas.1813775116 |pmid=30617061 |pmc=6347671 |bibcode=2019PNAS..116.1331Y |doi-access=free}}</ref> While genetics is not the exclusive cause of mating systems within animals, it is influential in many animals, particularly [[rodent]]s, which have been the most heavily researched. Certain rodents’ mating systems—monogamous, polygynous, or socially monogamous with frequent promiscuity—are correlated with suggested evolutionary [[Phylogenetic tree|phylogenies]], where rodents more closely related genetically are more likely to use a similar mating system, suggesting an evolutionary basis. These differences in mating strategy can be traced back to a few significant [[allele]]s that affect behaviors that are heavily influential on mating system, such as the alleles responsible for the level of parental care, how animals choose their partner(s), and sexual competitiveness, among others, which are all at least partially influenced by genetics.<ref name="Sinervo 2020">{{cite journal |last1=Sinervo |first1=Barry |last2=Chaine |first2=Alexis S. |last3=Miles |first3=Donald B. |title=Social Games and Genic Selection Drive Mammalian Mating System Evolution and Speciation |journal=The American Naturalist |date=February 2020 |volume=195 |issue=2 |pages=247–274 |doi=10.1086/706810|pmid=32017620 |bibcode=2020ANat..195..247S |s2cid=208584558 |url=https://hal.archives-ouvertes.fr/hal-03013292/file/Sinervo%20rodent%20mating%20systems.pdf }}</ref> While these genes may not perfectly correlate with the mating system that animals use, genetics is one factor that may lead to a species or population reproducing using one mating system over another, or even potentially multiple at different locations or points in time.

Mating systems can also have large impacts on the genetics of a population, strongly affecting natural selection and speciation. In [[plover]] populations, polygamous species tend to speciate more slowly than monogamous species do. This is likely because polygamous animals tend to move larger distances to find mates, contributing to a high level of [[gene flow]], which can genetically homogenize many nearby subpopulations. Monogamous animals, on the other hand, tend to stay closer to their starting location, not dispersing as much.<ref name="D'Urban 2017">{{cite journal |last1=D'Urban Jackson |first1=Josephine |last2=Dos Remedios |first2=Natalie |last3=Maher |first3=Kathryn H. |last4=Zefania |first4=Sama |last5=Haig |first5=Susan |last6=Oyler-McCance |first6=Sara |last7=Blomqvist |first7=Donald |last8=Burke |first8=Terry |last9=Bruford |first9=Michael W. |last10=Székely |first10=Tamás |last11=Küpper |first11=Clemens |title=Polygamy slows down population divergence in shorebirds. |journal=Evolution |date=May 2017 |volume=71 |issue=5 |pages=1313–1326 |doi=10.1111/evo.13212 |pmid=28233288 |pmc=5484996|bibcode=2017Evolu..71.1313J }}</ref> Because monogamous animals don’t migrate as far, monogamous populations which are geographically closer together tend to reproductively isolate from each other more easily, and thus each subpopulation is more likely to diversify or speciate from the other nearby populations as compared to polygamous populations. In polygamous species, however, the male partner in polygynous species and female partner in polyandrous species often tend to spread further to look for mates, potentially to find more or better mates. The increased level of movement among populations leads to increased gene flow between populations, effectively making geographically distinct populations into genetically similar ones via interbreeding.<ref name="Ritchie 2007">{{cite journal |last1=Ritchie |first1=Michael G. |title=Sexual Selection and Speciation |journal=Annual Review of Ecology, Evolution, and Systematics |date=1 December 2007 |volume=38 |issue=1 |pages=79–102 |doi=10.1146/annurev.ecolsys.38.091206.095733}}</ref> This has been observed in some species of rodents, where generally promiscuous species were quickly differentiated into monogamous and polygamous [[Taxon|taxa]] by a prominent introduction of monogamous behaviors in some populations of that species, showing the swift evolutionary effects different mating systems can have. Specifically, monogamous populations speciated up to 4.8 times faster and had lower extinction rates than non monogamous populations.<ref name="Sinervo 2020"/> Another way that monogamy has the potential to cause increased speciation is because individuals are more selective with partners and competition, causing different nearby populations of the same species to stop interbreeding as much, leading to speciation down the road.<ref name="Ritchie 2007"/>

Another potential effect of polyandry in particular is increasing the quality of offspring and reducing the probability of reproductive failure.<ref name="Holman 2013">{{cite journal |last1=Holman |first1=Luke |last2=Kokko |first2=Hanna |title=The consequences of polyandry for population viability, extinction risk and conservation |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=5 March 2013 |volume=368 |issue=1613 |doi=10.1098/rstb.2012.0053 |pmid=23339244 |pmc=3576587}}</ref> There are many possible reasons for this, one of the possibilities being that there is greater genetic variation in families because most offspring in a family will have either a different mother or father.<ref name="Firman 2012">{{cite journal |last1=Firman |first1=Renée C. |last2=Simmons |first2=Leigh W. |title=Male house mice evolving with post-copulatory sexual selection sire embryos with increased viability: Post-copulatory sexual selection and embryo viability in mice |journal=Ecology Letters |date=January 2012 |volume=15 |issue=1 |pages=42–46 |doi=10.1111/j.1461-0248.2011.01706.x|pmid=22011211 }}</ref> This reduces the potential harm done by inbreeding, as siblings will be less closely related and more genetically diverse. Additionally, because of the increased genetic diversity among generations, the levels of [[Fitness (biology)|reproductive fitness]] are also more variable, and so it is easier to select for positive traits more quickly, as the difference in fitness between members of the same generation would be greater. When many males are actively mating, polyandry can decrease the risk of extinction as well, as it can increase the [[effective population size]]. Increased effective population sizes are more stable and less prone to accumulating deleterious mutations due to genetic drift.<ref name="Firman 2012"/>