Editing Assortative mating (section)

== In humans ==
{{See also|1=Human mating strategies}}
Assortative mating in humans has been widely observed and studied, and can be broken down into two types of human assortative mating.<ref>{{Cite web |title=Assortative Mating and Income Inequality |url=https://www.nber.org/digest/may14/assortative-mating-and-income-inequality |access-date=2024-07-19 |website=NBER |language=en}}</ref> These are: 

* genetic assortative mating (assortative mating with mate choice based on genetic type and phenotypical expression); and
* social assortative mating (assortative mating with mate choice based on social, cultural, and other societal factors)

Genetic assortative mating is well studied and documented. In 1903 Pearson and colleagues reported strong correlations in height, span of arms, and the length of the left forearm between husband and wife in 1000 couples.<ref>{{Cite journal|date=1903-01-01|title=Assortative Mating in Man: A Cooperative Study|jstor=2331510|journal=Biometrika|volume=2|issue=4|pages=481–498|doi=10.2307/2331510}}</ref> Assortative mating with regards to appearance does not end there. Males prefer female faces that resemble their own when provided images of three women, with one image modified to resemble their own. However, the same result does not apply to females selecting male faces.<ref>{{Cite journal|last1=Kocsor|first1=Ferenc|last2=Rezneki|first2=Rita|last3=Juhász|first3=Szabolcs|last4=Bereczkei|first4=Tamás|date=2011-12-01|title=Preference for Facial Self-Resemblance and Attractiveness in Human Mate Choice |journal=Archives of Sexual Behavior|language=en|volume=40|issue=6|pages=1263–1270|doi=10.1007/s10508-010-9723-z|pmid=21267643|s2cid=2920533|issn=0004-0002}}</ref> Genetically related individuals (3rd or 4th cousin level) exhibit higher [[Fitness (biology)|fitness]] than unrelated individuals.<ref>{{Cite journal |last1=Helgason |first1=Agnar |last2=Pálsson |first2=Snæbjörn |last3=Guðbjartsson |first3=Daníel F. |last4=Kristjánsson |first4=þórður |last5=Stefánsson |first5=Kári |date=2008-02-08 |title=An Association Between the Kinship and Fertility of Human Couples |url=https://www.science.org/doi/10.1126/science.1150232 |journal=Science |language=en |volume=319 |issue=5864 |pages=813–816 |doi=10.1126/science.1150232 |pmid=18258915 |bibcode=2008Sci...319..813H |s2cid=17831162 |issn=0036-8075|url-access=subscription }}</ref>

Assortative mating based on genomic similarities plays a role in human marriages in the United States. Spouses are more genetically similar to each other than two randomly chosen individuals.<ref>{{Cite journal|last1=Guo|first1=Guang|last2=Wang|first2=Lin|last3=Liu|first3=Hexuan|last4=Randall|first4=Thomas|date=2014 |title=Genomic Assortative Mating in Marriages in the United States|journal=PLOS ONE|volume=9|issue=11|pages=e112322|doi=10.1371/journal.pone.0112322|issn=1932-6203|pmc=4226554|pmid=25384046|bibcode=2014PLoSO...9k2322G|doi-access=free}}</ref> The probability of marriage increases by roughly 15% for every one [[standard deviation]] increase in genetic similarity. However, some researchers argue that this assortative mating is caused purely by [[population stratification]] (the fact that people are more likely to marry within ethnic subgroups such as Swedish-Americans).<ref>{{Cite journal|last1=Abdellaoui|first1=Abdel|last2=Verweij|first2=Karin J. H.|last3=Zietsch|first3=Brendan P.|date=2014-10-07|title=No evidence for genetic assortative mating beyond that due to population stratification |journal=Proceedings of the National Academy of Sciences|language=en|volume=111|issue=40|pages=E4137|doi=10.1073/pnas.1410781111|issn=0027-8424|pmc=4210009|pmid=25232036|bibcode=2014PNAS..111E4137A|doi-access=free}}</ref>

At the same time, individuals display disassortative mating for genes in the major histocompatibility complex region on [[chromosome 6]]. Individuals feel more attracted to odors of individuals who are genetically different in this region. This promotes [[Major histocompatibility complex|MHC]] heterozygosity in the children, making them less vulnerable to pathogens. Apart from humans, [[Major histocompatibility complex and sexual selection|disassortative mating with regards to the MHC]] coding region has been widely studied in mice, and has also been reported to occur in fish.<ref>{{Cite journal|last1=Chaix|first1=Raphaëlle|last2=Cao|first2=Chen|last3=Donnelly|first3=Peter|date=2008-09-12|title=Is Mate Choice in Humans MHC-Dependent?|journal=PLOS Genetics|volume=4|issue=9|pages=e1000184|doi=10.1371/journal.pgen.1000184|issn=1553-7404|pmc=2519788|pmid=18787687 |doi-access=free }}</ref>

In addition to genetic assortative mating, humans also demonstrate patterns of assortative mating based on [[Sociology|sociological]] factors as well. Sociological assortative mating is typically broken down into three categories, mate choice based on [[Socioeconomic status|socio-economic status]], mate choice based on racial or ethnic background, and mate choice based on religious beliefs.<ref name=":0">{{Cite journal|last=Schwartz|first=Christine R.|title=Trends and Variation in Assortative Mating: Causes and Consequences |journal=Annual Review of Sociology|language=en|volume=39|issue=1|pages=451–470|doi=10.1146/annurev-soc-071312-145544|year=2013}}</ref>

Assortative mating based on socio-economic status is the broadest of these general categories. It includes the tendency of humans to prefer to mate within their socio-economic peers, that is, those with similar social standing, job prestige, educational attainment, or economic background as they themselves. This tendency has always been present in society: there was no historical area when most of the individuals preferred to sort, and had actually sorted, negatively into couples or matched randomly along these traits.<ref name=":0" /><ref name=":1">{{Cite journal|last=Mare|first=Robert D.|date=1991-01-01|title=Five Decades of Educational Assortative Mating|jstor=2095670|journal=American Sociological Review|volume=56|issue=1|pages=15–32|doi=10.2307/2095670}}</ref> Still, this tendency was weaker in some generations than in others. For instance, in the 20th century in the Western world, late Boomers had weaker aggregate preferences for educational homogamy than early Boomers had when being young adults; also, the members of the early Generation-X were typically much less "picky" about spousal education than the members of the late Generation-X were.  <ref>{{cite journal |last1=Naszodi |first1=A. |last2=Mendonca |first2=F. |year=2021 |title=A new method for identifying the role of marital preferences at shaping marriage patterns |journal=[[Journal of Demographic Economics]] |volume=1 |issue=1 |pages=1–27 |doi=10.1017/dem.2021.1 |doi-access=free}}</ref> This  trend is evidenced by the search criteria of online dating site users.<ref>{{cite journal |last1=Naszodi |first1=A. |last2=Mendonca |first2=F. |year=2022 |title=Changing educational homogamy: Shifting preferences or evolving educational distribution? |journal=[[Journal of Demographic Economics]] |volume=1 |issue=1 |pages=1–29 |doi=10.1017/dem.2022.21 |doi-access=free}}</ref>

Another form of sociological assortative mating is assortative mating based on racial and ethnic background. Mentioned above in the context of the genetically similar preferring to mate with one another, this form of assortative mating can take many varied and complicated forms. While the tendency mentioned above does exist, and people do tend to marry those genetically similar to themselves, especially if within the same racial or ethnic group, this trend can change in various ways. It is common, for example, for the barriers to intermarriage with the general population experienced by a minority population to decrease as the numbers of the minority population increase. This assimilation reduces the prevalence of this form of assortative mating. However, growth of a minority population does not necessarily lead to decreased barriers to intermarriage. This can be seen in the sharp increase in the non-white Hispanic population of the United States in the 1990s and 2000s that correlated with a sharp decrease in the percentage of non-white Hispanics intermarrying with the general population.<ref name=":0" />

Religious assortative mating is the tendency of individuals to marry within their own religious group. This tendency is prevalent and observable, and changes according to three main factors. The first of these is the proportion of available spouses in the area who already follow the same religion as the person searching for a mate. Areas where religious beliefs are already similar for most people will always have high degrees of religious inbreeding. The second is the social distance between the intermarrying religious groups, or the physical proximity and social interactivity of these groups. Finally, the third factor is the personal views one holds towards marrying outside of a religion. Those who greatly value adherence to religious tradition may be more likely to be averse to marrying across religious lines.<ref>{{Cite book |title=Religious Assortative Marriage|year=1980|publisher=Academic Press|isbn=978-0123865809|editor-last=Johncon|editor-first=RobertR Alan|pages=ii|doi=10.1016/b978-0-12-386580-9.50001-6}}</ref> Although not necessarily religious, a good example of humans mating assortatively based on belief structure can be found in the tendency of humans to marry based on levels of charitable giving. Couples show similarities in terms of their contributions to public betterment and charities, and this can be attributed to mate choice based on generosity rather than phenotypic convergence.<ref>{{Cite journal|last1=Tognetti|first1=A.|last2=Berticat|first2=C.|last3=Raymond|first3=M.|last4=Faurie|first4=C.|date=2014-05-01|title=Assortative mating based on cooperativeness and generosity |journal=Journal of Evolutionary Biology|language=en|volume=27|issue=5|pages=975–981|doi=10.1111/jeb.12346|pmid=24581285|issn=1420-9101|doi-access=free}}</ref>

Assortative mating also occurs among people with mental disorders such as ADHD, in which one person with ADHD is more likely to marry or have a child with another individual with ADHD.<ref>{{Cite journal|last1=Nordsletten|first1=Ashley E.|last2=Larsson|first2=Henrik|last3=Crowley|first3=James J.|last4=Almqvist|first4=Catarina|date=2016|title=Patterns of Nonrandom Mating Within and Across 11 Major Psychiatric Disorders|journal=JAMA Psychiatry|volume=73|issue=4|pages=354–361|doi=10.1001/jamapsychiatry.2015.3192|pmid=26913486|pmc=5082975}}</ref>