View source for Philosophy:Sexual selection in humans

{{short description|Evolutionary effects of sexual selection on humans}}
'''Sexual selection in humans''' concerns the concept of [[Biology:Sexual selection|sexual selection]], introduced by [[Biography:Charles Darwin|Charles Darwin]] as an element of his theory of [[Biology:Natural selection|natural selection]],<ref name="PHYS-20140129">{{cite news |last=Vogt |first=Yngve |title=Large testicles are linked to infidelity |url=http://phys.org/news/2014-01-large-testicles-linked-infidelity.html |date=29 January 2014 |work=Phys.org |access-date=31 January 2014 }}</ref> as it affects [[Biology:Human|human]]s. Sexual selection is a biological way one sex chooses a mate for the best reproductive success. Most compete with others of the same sex for the best mate to contribute their genome for future generations. This has shaped human evolution for many years, but reasons why humans choose their mates are not fully understood. Sexual selection is quite different in non-human animals than humans as they feel more of the evolutionary pressures to reproduce and can easily reject a mate.<ref name="Miller G 2000" /> The role of sexual selection in [[Biology:Human evolution|human evolution]] has not been firmly established although [[Biology:Neoteny|neoteny]] has been cited as being caused by human sexual selection.<ref>{{Cite web|url=http://www.davidbrin.com/nonfiction/neoteny1.html|author=Brin, David|title= Neoteny and Two-Way Sexual Selection in Human Evolution|website=www.davidbrin.com}}</ref> It has been suggested that sexual selection played a part in the evolution of the anatomically modern human brain, i.e. the structures responsible for social intelligence underwent positive selection as a sexual ornamentation to be used in courtship rather than for survival itself,<ref>{{Cite web|url=https://www.edge.org/conversation/sexual-selection-and-the-mind|title=Sexual Selection and the Mind|website=www.edge.org}}</ref> and that it has developed in ways outlined by [[Biography:Ronald Fisher|Ronald Fisher]] in the [[Biology:Fisherian runaway|Fisherian runaway]] model.<ref name="fisher30">Fisher, R.A. (1930) The Genetical Theory of Natural Selection. {{ISBN|0198504403}}</ref><ref name="pers00">Edwards, A.W.F. (2000) Perspectives: Anecdotal, Historical and Critical Commentaries on Genetics. The Genetics Society of America (154) 1419:1426</ref><ref name="ander94">Andersson, M. (1994) Sexual selection. {{ISBN|0691000573}}</ref><ref name="ander06">Andersson, M. and Simmons, L.W. (2006) Sexual selection and mate choice. Trends, Ecology and Evolution (21) 296:302</ref><ref name="gayon10">Gayon, J. (2010) Sexual selection: Another Darwinian process. Comptes Rendus Biologies (333) 134:144</ref> Fisher also stated that the development of sexual selection was "more favourable" in humans.<ref name="Fisher 1915a">{{cite journal | last1 = Fisher | first1 = R. A. | year = 1915 | title = The evolution of sexual preference | journal = Eugenics Review | volume = 7 | issue = 3| pages = 184–192 |pmc=2987134 | pmid=21259607}}</ref>

==General hypotheses==
Some hypotheses about the evolution of the human brain argue that it is a sexually selected trait, as it would not confer enough fitness in itself relative to its high maintenance costs (a fifth to a quarter of the energy and oxygen consumed by a human).<ref>{{cite journal | author = Schillaci, M. A. | year = 2006 | title = Sexual selection and the evolution of brain size in primates | journal = PLOS ONE | volume = 1 | issue = 1 | page = e62 | doi=10.1371/journal.pone.0000062 | pmid=17183693 | pmc=1762360| bibcode=2006PLoSO...1...62S | doi-access = free }} {{open access}}</ref> Current consensus about the evolutionary development of the human brain accepts sexual selection as a potential contributing factor but maintains that human intelligence and the ability to store and share cultural knowledge would have likely carried high survival value as well.<ref>{{Cite journal|last=McElreath|first=Richard|date=May 2018|title=Sizing up human brain evolution|journal=Nature|volume=557|issue=7706|pages=496–497|doi=10.1038/d41586-018-05197-8|pmid=29789743|bibcode=2018Natur.557..496M|doi-access=free}}</ref>

Sexual selection's role in human evolution cannot be definitively established, as features may result from an equilibrium among competing selective pressures, some involving sexual selection, others [[Biology:Natural selection|natural selection]], and others [[Biology:Pleiotropy|pleiotropy]]. [[Biography:Richard Dawkins|Richard Dawkins]] argued that
: "When you notice a characteristic of an animal and ask what its Darwinian survival value is, you may be asking the wrong question. It could be that the characteristic you have picked out is not the one that matters.  It may have "come along for the ride", dragged along in evolution by some other characteristic to which it is pleiotropically linked."<ref>{{cite book|author=Richard Dawkins|title=The Greatest Show on Earth: The Evidence for Evolution|url=https://books.google.com/books?id=CQdDhIgKM4UC&pg=PT67|year=2009|publisher=Simon and Schuster|isbn=978-1416597780|page=67}}</ref>

==Darwin's sexual selection hypothesis==
[[Biography:Charles Darwin|Charles Darwin]] described [[Biology:Sexual selection|sexual selection]] as depending on "the advantage which certain individuals have over others of the same sex and species, solely in respect of reproduction".<ref name=DarwinDescent256>{{cite book | author = Darwin, Charles | url = http://darwin-online.org.uk/content/frameset?pageseq=269&itemID=F937.1&viewtype=side | title = The Descent of Man and Selection in Relation to Sex | location = London | publisher = John Murray | year = 1871 | volume = 1 | edition = 1st | page = 256}}</ref> Darwin noted that sexual selection is of two kinds and concluded that both kinds had operated on humans:<ref name=DarwinDescent402>{{cite book | author = Darwin, Charles | url = http://darwin-online.org.uk/content/frameset?pageseq=419&itemID=F937.2&viewtype=sidee | title = The Descent of Man and Selection in Relation to Sex | location = London | publisher = John Murray | year = 1871 | volume = 2 | edition = 1st | page = 402}}</ref> "The sexual struggle is of two kinds; in the one it is between the individuals of the same sex, generally the male sex, in order to drive away or kill their rivals, the females remaining passive; whilst in the other, the struggle is likewise between the individuals of the same sex, in order to excite or charm those of the opposite sex, generally the females, which no longer remain passive, but select the more agreeable partners."<ref name=DarwinDescent398>{{cite book | author = Darwin, Charles | url = http://darwin-online.org.uk/content/frameset?pageseq=269&itemID=F937.1&viewtype=side | title = The Descent of Man and Selection in Relation to Sex | location = London | publisher = John Murray | year = 1871 | volume = 1 | edition = 1st | page = 398}}</ref>

Charles Darwin conjectured that the male beard, as well as the hairlessness of humans compared to nearly all other mammals, were results of sexual selection. He reasoned that since the bodies of females are more nearly hairless, the loss of fur was due to sexual selection of females at a remote prehistoric time when males had overwhelming selective power, and that it nonetheless affected males due to genetic correlation between the sexes. He also hypothesized that contrasts in sexual selection acting along with natural selection were significant factors in the geographical differentiation in human appearance of some isolated groups, as he did not believe that [[Biology:Natural selection|natural selection]] alone provided a satisfactory answer. Although not explicit, his observation that in Khoisan women "the posterior part of the body projects in a most wonderful manner" (known as [[Medicine:Steatopygia|steatopygia]])<ref>{{cite book | title = The Descent of Man and Selection in Relation to Sex | author = Charles Darwin | year = 1882 | location = London | publisher = John Murray | page = 578 | url = http://darwin-online.org.uk/content/frameset?itemID=F955&viewtype=text&pageseq=1}}</ref> implies sexual selection for this characteristic. In ''The Descent of Man, and Selection in Relation to Sex'', Darwin viewed many physical traits which vary around the world as being so trivial to survival<ref name="Darwin1882">{{cite book|author=Charles Darwin|title=The Descent of Man, and Selection in Relation to Sex|url=https://archive.org/details/descentmanandse14darwgoog|year=1882|publisher=AMS Press|pages=[https://archive.org/details/descentmanandse14darwgoog/page/n627 605]|isbn=978-0404084097|quote=The races of man differ from each other, and from their nearest allies, in certain characters which are of no service to them in their daily habits of life, and which it is extremely probable would have been modified through sexual selection}}</ref> that he concluded some input from sexual selection was required to account for their presence. He noted that variation in these features among the various peoples of the world meant human mate-choice criteria would also have to be quite different if the focus was similar, and he himself doubted that, citing<ref>Darwin, C. (1936) [1888]. ''The Descent of Man and Selection in Relation to Sex''. reprint of 2nd ed., The Modern Library, New York: Random House.</ref> reports indicating that ideals of beauty did not, in fact, vary in this way around the world.

==Sexual dimorphism==
{{main|Biology:Sexual dimorphism}}
{{Further|Philosophy:Sex differences in humans}}

The effects on the human brain formation during puberty is directly linked to hormones changes.  The mismatch timing between biological puberty and age of social maturity in western society has a psychological expectation on children.<ref>{{cite journal |last1=Gluckman |first1=P. D. |last2=Hanson |first2=M. A. |title=Changing times: The evolution of puberty |journal=Molecular and Cellular Endocrinology |volume=254–255 |pages=26–31 |doi=10.1016/j.mce.2006.04.005 |pmid=16713071 |date=25 July 2006|s2cid=8724902 }}</ref> With puberty, men are generally hairier than women, and Darwin was of the opinion that hairlessness was related to sexual selection; however, several other explanations have been advanced to explain human hairlessness; a leading one being that loss of body hair facilitated sweating.<ref name=Jablonski06>Jablonski, N. G. (2006). ''[https://archive.org/details/skinnaturalhisto00jabl Skin: a natural history].'' Berkeley, CA: University of California Press. p. PP13.</ref> This idea closely relates to that of the suggested need for increased [[Physics:Photoprotection|photoprotection]] and is part of the most-commonly-accepted scientific explanation for the evolution of pigmentary traits.<ref name="pmid 20445093">{{Cite journal | last1 = Jablonski | first1 = N. G. | last2 = Chaplin | first2 = G.
| doi = 10.1073/pnas.0914628107 | title = Human skin pigmentation as an adaptation to UV radiation | journal = Proceedings of the National Academy of Sciences | volume = 107 | issue = Suppl 2 | pages = 8962–8968 | year = 2010 | pmid = 20445093 | pmc =3024016| bibcode = 2010PNAS..107.8962J | doi-access = free }}</ref>

Sexual dimorphism suggests the presence of sexual selection. The earliest [[Biology:Homininae|homininae]] were highly dimorphic and that this tendency lessened over the course of human evolution, suggesting humans have become more monogamous. In contrast, [[Biology:Gorilla|gorilla]]s living in harems exhibit a much stronger sexual dimorphism (see: [[Biology:Homininae|homininae]]).<ref>''Principles of Human Evolution'', by Roger Lewin, Robert Foley. {{page needed|date=March 2022}}</ref>

===Sexual anatomy===

The theory of sexual selection has been used to explain a number of [[Medicine:Human body|human anatomical]] features. These include rounded breasts, [[Medicine:Facial hair|facial hair]], pubic hair and penis size. The breasts of primates are flat, yet are able to produce sufficient milk for feeding their young. The breasts of non-lactating human females are filled with fatty tissue and not milk. Thus it has been suggested the rounded female breasts are signals of fertility.<ref name="nakedwoman">{{cite book |title=The Naked Woman|last=Morris |first=Desmond |chapter=Breasts|chapter-url=https://books.google.com/books?id=Wa9zntiEKeAC&pg=PA144 |year=2007 |publisher=Macmillan |isbn= 978-0312338534}}</ref> Richard Dawkins has speculated that the loss of the [[Biology:Baculum|penis bone]] in humans, when it is present in other primates, may be due to sexual selection by females looking for a clear sign of good health in prospective mates. Since a human erection relies on a hydraulic pumping system, erection failure is a sensitive early warning of certain kinds of physical and mental ill health.<ref name="Dawkins 2006 p.158 endnote">{{cite book |last=Dawkins |first=Richard |author-link=Richard Dawkins |title=The Selfish Gene |orig-year=1976 |edition=30th anniversary |year=2006 |page=[https://archive.org/details/selfishgene00dawk_018/page/n182 158] endnote |quote=It is not implausible that, with natural selection refining their diagnostic skills, females could glean all sorts of clues about a male's health, and the robustness of his ability to cope with stress, from the tone and bearing of his penis. |title-link=The Selfish Gene }}</ref>

''Homo'' has a thicker penis than the other [[Biology:Hominidae|great apes]], though it is on average no longer than the [[Biology:Common chimpanzee|chimpanzee]]'s.<ref>{{cite book | author = Dixson, A. F. | year = 2009 | title = Sexual selection and the origins of human mating systems | publisher = Oxford University Press | pages = 61–65 | url = https://books.google.com/books?id=VRTniKE2liYC| isbn=978-0191569739 }}</ref> It has been suggested the [[Medicine:Human penis size#Evolution|evolution of the human penis towards larger size]] was the result of female choice rather than [[Philosophy:Sperm competition|sperm competition]], which generally favors large testicles.<ref>Miller, G.F. (1998), "How mate choice shaped human nature: A review of sexual selection and human evolution" in ''Handbook of Evolutionary Psychology''.</ref> However, penis size may have been subject to natural selection, rather than sexual selection, due to a larger penis' efficiency in displacing the sperm of rival males during [[Biology:Sexual intercourse|sexual intercourse]]. A model study showed displacement of semen was directly proportional to the depth of pelvic thrusting, as an efficient semen displacement device.<ref>In a {{usurped|1=[https://web.archive.org/web/20070114130537/http://www.epjournal.net/filestore/ep021223.pdf theoretical paper]}} published in the journal [http://www.scientificamerican.com/topic.cfm?id=evolutionary-psychology ''Evolutionary Psychology''] in 2004, Gallup and coauthor, Rebecca Burch, conjecture that, "A longer penis would not only have been an advantage for leaving semen in a less-accessible part of the vagina, but by filling and expanding the vagina, it also would aid and abet the displacement of semen left by other males as a means of maximizing the likelihood of paternity." – [http://www.scientificamerican.com/article.cfm?id=secrets-of-the-phallus "Secrets of the Phallus: Why Is the Penis Shaped Like That?"], ScientificAmerican.com.</ref>

== Selection preferences and biological drivers ==

{{main|Biology:Mate choice in humans}}

There are a variety of factors that drive sexual selection in humans. Current available research indicates that selection preferences are biologically driven,<ref name="Grammer 385–407">{{Cite journal|last1=Grammer|first1=Karl|last2=Fink|first2=Bernhard|last3=Møller|first3=Anders P.|last4=Thornhill|first4=Randy|date=1 August 2003|title=Darwinian aesthetics: sexual selection and the biology of beauty|journal=Biological Reviews|volume=78|issue=3|pages=385–407|doi=10.1017/s1464793102006085|pmid=14558590|s2cid=25257668|issn=1469-185X}}</ref> that is, by the display of [[Biology:Phenotypic trait|phenotypic trait]]s that can be both consciously and unconsciously evaluated by the opposite sex to determine the health and fertility of a potential mate.<ref name="Rhodes S93–S95">{{Cite journal|last1=Rhodes|first1=Gillian|last2=Chan|first2=Janelle|last3=Zebrowitz|first3=Leslie A.|last4=Simmons|first4=Leigh W.|date=7 August 2003|title=Does sexual dimorphism in human faces signal health?|journal=Proceedings of the Royal Society of London B: Biological Sciences|volume=270|issue=Suppl 1|pages=S93–S95|doi=10.1098/rsbl.2003.0023|issn=0962-8452|pmc=1698019|pmid=12952647}}</ref> This process can be affected, however, by social factors, including in cultures where arranged marriage is practiced, or [[Social:Psychosocial|psychosocial]] factors, such as valuing certain cultural traits of a mate, including a person's [[Social:Social status|social status]], or what is perceived to be an ideal partner in various cultures.<ref name="Price e52532">{{Cite journal|last1=Price|first1=Michael E. |last2=Pound |first2=Nicholas |last3=Dunn|first3=James |last4=Hopkins|first4=Sian |last5=Kang|first5=Jinsheng |date=2 January 2013|title=Body Shape Preferences: Associations with Rater Body Shape and Sociosexuality |journal=PLOS ONE|volume=8|issue=1|pages=e52532 |doi=10.1371/journal.pone.0052532 |pmc=3534680 |pmid=23300976 |bibcode=2013PLoSO...852532P |doi-access=free}}</ref>

=== Selection preferences in females ===
Some of the factors that affect how females select their potential mates for reproduction include voice pitch, facial shape, muscular appearance, and height.<ref>{{cite book |last=Buss |first=David |date=2019 |edition=6th |title=Evolutionary Psychology: The New Science of the Mind |chapter=Women's Long-Term Mating Strategies |url=https://books.google.com/books?id=Sn6JDwAAQBAJ |publisher=Routledge |isbn=978-0429590061 }}</ref><ref name=":0">{{Cite journal |last1=Feinberg |first1=D. R. |last2=Jones |first2=B. C. |last3=Law Smith|first3=M. J. |last4=Moore|first4=F. R. |last5=DeBruine|first5=L. M. |last6=Cornwell|first6=R. E.|last7=Hillier |first7=S. G. |last8=Perrett|first8=D. I. |date=1 February 2006|title=Menstrual cycle, trait estrogen level, and masculinity preferences in the human voice|journal=Hormones and Behavior |volume=49 |issue=2 |pages=215–222 |doi=10.1016/j.yhbeh.2005.07.004 |pmid=16055126 |s2cid=14884832}}</ref> Several studies suggest that there is a link between hormone levels and partner selection among humans. In a study measuring female attraction to males with varying levels of [[Social:Masculinity|masculinity]], it was established that women had a general masculinity preference for men's voices, and that the preference for masculinity was greater in the fertile phase of the [[Medicine:Menstrual cycle|menstrual cycle]] than in the non-fertile phase.<ref name=":0" /> There is further evidence from the same study that in fertile stages of the menstrual cycle, women also had a preference for other masculine traits such as body size, facial shape, and dominant behavior, which are indicators of both fertility and health.<ref name=":0" /> This study did not exclude males with feminine traits from being selected, however, as feminine traits in men indicate a higher probability of long-term relationship commitment,<ref name=":0" /> and may be one of several evolutionary strategies.<ref>{{cite web|title=Strategies for Animal Survival 2 (Animal Studies Series)|url=https://www.kanopystreaming.com/product/strategies-animal-survival-2|publisher=Chip Taylor Communications}}</ref> Further research also backs up the idea of using [[Biology:Phenotypic trait|phenotypic trait]]s as a means of assessing a potential mate's [[Biology:Fitness|fitness]] for [[Biology:Reproduction|reproduction]] as well as assessing whether a partner has high genetic quality.<ref>{{cite journal|title=Influence of female 2D:4D ratio on attractiveness of male vocal and facial masculinity|date=2009|author=Shaw, Fionna|type=Dissertation|hdl = 1842/3604}}</ref>

Another factor affecting the selection process is the environment which the person inhabits. In biological terms, certain environmental conditions may bring about demands for or the disregarding of certain traits. One such example is a preference for males whose facial structure indicates certain hormonal ratios, such as [[Chemistry:Testosterone|testosterone]]-[[Chemistry:Cortisol|cortisol]] levels (sex and stress hormones). Research shows that, for example, in countries with varying [[Engineering:Human Development Index|Human Development Index]] (HDI) levels, females have different preferences for sex-stress hormone ratios, as expressed in the male's face. A Royal Society research showed a significant correlation between a measure of societal development and preferences for indication of lower testosterone levels, as manifested in facial features, and the interaction between preferences for testosterone and cortisol.<ref name=":1">{{Cite journal|last1=Moore|first1=F. R.|last2=Coetzee|first2=V.|last3=Contreras-Garduño|first3=J.|last4=Debruine|first4=L. M.|last5=Kleisner|first5=K.|last6=Krams|first6=I.|last7=Marcinkowska|first7=U.|last8=Nord|first8=A.|last9=Perrett|first9=D. I.|date=23 June 2013|title=Cross-cultural variation in women's preferences for cues to sex- and stress-hormones in the male face|journal=Biology Letters|volume=9|issue=3|pages=20130050|doi=10.1098/rsbl.2013.0050|issn=1744-9561|pmc=3645036|pmid=23536442}}</ref> It was concluded that societal-level ecological factors impact the valuation of traits by combinations of sex- and stress-hormones.<ref name=":1" />

A 2020 study reported that women tend to find a man more attractive if the man's previous relationships ended mutually, and less attractive if the man was dumped.<ref>{{Cite journal |doi = 10.1007/s40806-020-00239-9|title = Female Mate Copying: Measuring the Effect of Mate-Relevant Information Provided by Former Partners|year = 2020|last1 = Scammell|first1 = Emily|last2 = Anderson|first2 = Ryan C.|journal = Evolutionary Psychological Science|volume = 6|issue = 4|pages = 319–327|s2cid = 218948364|doi-access = free}}</ref>

=== Selection preferences in males ===
Like their female counterparts, males also use visual information about a potential mate, as well as voice, body shape, and an assortment of other factors in selecting a partner. Research shows that males tend to prefer feminine women's faces and voices as opposed to women with masculine features in these categories.<ref name=":2">{{Cite journal|last1=O'Connor|first1=Jillian J. M.|last2=Fraccaro|first2=Paul J.|last3=Pisanski|first3=Katarzyna|last4=Tigue|first4=Cara C.|last5=Feinberg|first5=David R.|date=31 July 2013|title=Men's Preferences for Women's Femininity in Dynamic Cross-Modal Stimuli|journal=PLOS ONE|volume=8|issue=7|pages=e69531|doi=10.1371/journal.pone.0069531|issn=1932-6203|pmc=3729951|pmid=23936037|bibcode=2013PLoSO...869531O|doi-access=free}}</ref> Furthermore, males also evaluate skin coloration, [[Biology:Symmetry in biology|symmetry]], and apparent health, as a means by which they select a partner for reproductive purposes.<ref name=":2" /> Males are particularly attracted to femininity in women's faces when their testosterone levels are at their highest, and the level of attraction to femininity may fluctuate as hormone levels fluctuate.<ref>{{Cite journal|last1=Welling|first1=Lisa L. M.|last2=Jones|first2=Benedict C.|last3=DeBruine|first3=Lisa M.|last4=Smith|first4=Finlay G.|last5=Feinberg|first5=David R.|last6=Little|first6=Anthony C.|last7=Al-Dujaili|first7=Emad A. S.|date=1 November 2008|title=Men report stronger attraction to femininity in women's faces when their testosterone levels are high|journal=Hormones and Behavior|volume=54|issue=5|pages=703–708|doi=10.1016/j.yhbeh.2008.07.012|pmid=18755192|s2cid=205803606}}</ref> Studies on men have also been done to show the effects of [[Chemistry:Testosterone (medication)|exogenous testosterone]] and its effects on attraction to femininity, and the results concluded that throughout several studies, men have shown decreased preference for feminine female faces in the long-term context, when given exogenous testosterone, but this difference did not occur with [[Medicine:Placebo|placebo]].<ref>{{Cite journal|last1=Bird|first1=Brian M.|last2=Welling|first2=Lisa L. M.|last3=Ortiz|first3=Triana L.|last4=Moreau|first4=Benjamin J. P.|last5=Hansen|first5=Steve|last6=Emond|first6=Michael|last7=Goldfarb|first7=Bernard|last8=Bonin|first8=Pierre L.|last9=Carré|first9=Justin M.|date=1 September 2016|title=Effects of exogenous testosterone and mating context on men's preferences for female facial femininity|url= https://zone.biblio.laurentian.ca/handle/10219/2617|journal=Hormones and Behavior|volume=85|pages=76–85|doi=10.1016/j.yhbeh.2016.08.003|pmid=27511452|s2cid=4130150}}</ref>

=== Common preferences in either sex ===
Sexual selection preferences are general terms by which the [[Biology:Mating|mating]] and reproductive process are understood. As one article states, sexual selection is in essence a process which favors sexual displays for attraction, aggressiveness, dominance, size, and strength, and the ability to exclude competitors by force if necessary, or by using resources to win.<ref>{{Cite journal|last1=Puts|first1=David A.|last2=Jones|first2=Benedict C.|last3=DeBruine|first3=Lisa M.|date=1 March 2012|title=Sexual Selection on Human Faces and Voices|journal=The Journal of Sex Research|volume=49|issue=2–3|pages=227–243|doi=10.1080/00224499.2012.658924|issn=0022-4499|pmid=22380590|citeseerx=10.1.1.699.7560|s2cid=27040803}}</ref> Both male and female use voice, face, and other physical characteristics<ref name="Price e52532"/> to assess a potential mate's ability to reproduce, as well as their health.<ref name="Rhodes S93–S95"/> Together with visual and chemical signals, these crucial characteristics which are likely to enhance the ability to produce [[Biology:Offspring|offspring]], as well as long-term [[Biology:Survival of the fittest|survival]] prospects, can be assessed and selections made.<ref name="Grammer 385–407"/><ref>{{cite web|url=http://necsi.edu/projects/evolution/evolution/5parts/evolution_5parts.html|title=How Does Evolution Occur?|work=necsi.edu}}</ref>

== Sexual selection in males ==

=== Contest competition ===
Contest competition is form of sexual selection in which mating is obtained by using force or the threat of force to exclude same-sex competitors from mates.<ref name=":3">Puts, D., Carrier, D., and Rogers, A.R. (in press). Contest competition for mates and the evolution of human males. In: ''Handbook of Human Mating''. Buss, D.M. and Durkee, P., eds. ''Oxford University Press''. {{ISBN?}}{{page needed|date=December 2022}}</ref> Male contest competition favors large body size, which is seen in the sexual dimorphism of human males and females.<ref>{{Cite journal |last1=Mitani |first1=J. C. |last2=Gros-Louis |first2=J. |last3=Richards |first3=A. F. |date=June 1996 |title=Sexual Dimorphism, the Operational Sex Ratio, and the Intensity of Male Competition in Polygynous Primates |url=http://dx.doi.org/10.1086/285888 |journal=The American Naturalist |volume=147 |issue=6 |pages=966–980 |doi=10.1086/285888 |s2cid=84857807 |issn=0003-0147}}</ref> In all living hominid species, males are more muscular, allowing them to have more strength and power. Human males have 61% more overall muscle mass compared to females.<ref>{{Cite journal |last=Abe |first=T |date=2003-10-01 |title=Sex differences in whole body skeletal muscle mass measured by magnetic resonance imaging and its distribution in young Japanese adults |url=http://dx.doi.org/10.1136/bjsm.37.5.436 |journal=British Journal of Sports Medicine |volume=37 |issue=5 |pages=436–440 |doi=10.1136/bjsm.37.5.436 |pmid=14514537 |pmc=1751351 |issn=0306-3674}}</ref> This greater muscle mass allows males to gain greater acceleration, speed, and more powerful striking movements.<ref>{{Cite journal |last1=Hoffman |first1=Steven G. |last2=Schildhauer |first2=Mark P. |last3=Warner |first3=Robert R. |date=July 1985 |title=The Costs of Changing Sex and the Ontogeny of Males Under Contest Competition for Mates |url=http://dx.doi.org/10.2307/2408690 |journal=Evolution |volume=39 |issue=4 |pages=915–927 |doi=10.2307/2408690 |jstor=2408690 |pmid=28561353 |issn=0014-3820}}</ref> Compared to females, human males exhibit more same-sex aggression, which peaks in young adulthood.<ref>{{Cite journal |last=Archer |first=John |date=December 2004 |title=Sex Differences in Aggression in Real-World Settings: A Meta-Analytic Review |url=http://dx.doi.org/10.1037/1089-2680.8.4.291 |journal=Review of General Psychology |volume=8 |issue=4 |pages=291–322 |doi=10.1037/1089-2680.8.4.291 |s2cid=26394462 |issn=1089-2680}}</ref><ref>{{Cite book |last1=Ellis |first1=Lee |last2=Hershberger |first2=Scott |last3=Field |first3=Evelyn |last4=Wersinger |first4=Scott |last5=Pellis |first5=Sergio |last6=Geary |first6=David |last7=Palmer |first7=Craig |last8=Hoyenga |first8=Katherine |last9=Hetsroni |first9=Amir |last10=Karadi |first10=Kazmer |date=2013-05-13 |title=Sex Differences |url=http://dx.doi.org/10.4324/9780203838051 |doi=10.4324/9780203838051|isbn=978-0203838051 }}</ref><ref>{{Cite journal |last=Ryan |first=Michael J. |date=1995-02-03 |title=Offsetting Advantages: ''Sexual Selection''. Malte Andersson. Princeton University Press, Princeton, NJ, 1994. 599 pp. |url=http://dx.doi.org/10.1126/science.267.5198.712 |journal=Science |volume=267 |issue=5198 |pages=712–713 |doi=10.1126/science.267.5198.712 |s2cid=220098656 |issn=0036-8075}}</ref><ref>{{Cite journal |last=Archer |first=John |date=August 2009 |title=Does sexual selection explain human sex differences in aggression? |url=https://www.cambridge.org/core/product/identifier/S0140525X09990951/type/journal_article |journal=Behavioral and Brain Sciences |language=en |volume=32 |issue=3–4 |pages=249–266 |doi=10.1017/S0140525X09990951 |pmid=19691899 |issn=0140-525X}}</ref>

Male contest competition also often favors threat displays, which allow one competitor to submit without a costly fight.<ref>{{Cite journal |last1=Smith |first1=John Maynard |last2=Parker |first2=G.A. |date=February 1976 |title=The logic of asymmetric contests |url=http://dx.doi.org/10.1016/s0003-3472(76)80110-8 |journal=Animal Behaviour |volume=24 |issue=1 |pages=159–175 |doi=10.1016/s0003-3472(76)80110-8 |s2cid=53161069 |issn=0003-3472}}</ref> Low vocalization fundamental frequencies (perceived as vocal pitch) increase the perception of threat among human males.<ref>{{Cite journal |last1=Hodges-Simeon |first1=Carolyn R. |last2=Gaulin |first2=Steven J. C. |last3=Puts |first3=David A. |date=December 2010 |title=Different Vocal Parameters Predict Perceptions of Dominance and Attractiveness |journal=Human Nature |language=en |volume=21 |issue=4 |pages=406–427 |doi=10.1007/s12110-010-9101-5 |issn=1045-6767 |pmc=2995855 |pmid=21212816}}</ref><ref>{{Cite journal |last1=Feinberg |first1=D.R. |last2=Jones |first2=B.C. |last3=Little |first3=A.C. |last4=Burt |first4=D.M. |last5=Perrett |first5=D.I. |date=March 2005 |title=Manipulations of fundamental and formant frequencies influence the attractiveness of human male voices |url=https://linkinghub.elsevier.com/retrieve/pii/S0003347204003987 |journal=Animal Behaviour |language=en |volume=69 |issue=3 |pages=561–568 |doi=10.1016/j.anbehav.2004.06.012|s2cid=205510863 }}</ref><ref>{{Cite journal |last1=Puts |first1=David Andrew |last2=Gaulin |first2=Steven J.C. |last3=Verdolini |first3=Katherine |date=July 2006 |title=Dominance and the evolution of sexual dimorphism in human voice pitch |url=https://linkinghub.elsevier.com/retrieve/pii/S1090513805000966 |journal=Evolution and Human Behavior |language=en |volume=27 |issue=4 |pages=283–296 |doi=10.1016/j.evolhumbehav.2005.11.003|s2cid=32562654 }}</ref> Controlling for body size, lower male fundamental frequency relative to females tends to evolve in polygynous anthropoid primates, where males compete more intensely for mates.<ref name=":4">{{Cite journal |last1=Puts |first1=David A. |last2=Hill |first2=Alexander K. |last3=Bailey |first3=Drew H. |last4=Walker |first4=Robert S. |last5=Rendall |first5=Drew |last6=Wheatley |first6=John R. |last7=Welling |first7=Lisa L. M. |last8=Dawood |first8=Khytam |last9=Cárdenas |first9=Rodrigo |last10=Burriss |first10=Robert P. |last11=Jablonski |first11=Nina G. |last12=Shriver |first12=Mark D. |last13=Weiss |first13=Daniel |last14=Lameira |first14=Adriano R. |last15=Apicella |first15=Coren L. |date=2016-04-27 |title=Sexual selection on male vocal fundamental frequency in humans and other anthropoids |url=http://dx.doi.org/10.1098/rspb.2015.2830 |journal=Proceedings of the Royal Society B: Biological Sciences |volume=283 |issue=1829 |pages=20152830 |doi=10.1098/rspb.2015.2830 |pmid=27122553 |pmc=4855375 |issn=0962-8452}}</ref> Chimpanzees and humans have the greatest sexual dimorphism in fundamental frequency of all hominids.<ref name=":4" /> Males are also more likely to engage in physical risks in front of competitors, and males who take more physical risks are perceived as being stronger.<ref>{{Cite journal |last1=Fessler |first1=Daniel M.T. |last2=Tiokhin |first2=Leonid B. |last3=Holbrook |first3=Colin |last4=Gervais |first4=Matthew M. |last5=Snyder |first5=Jeffrey K. |date=January 2014 |title=Foundations of the Crazy Bastard Hypothesis: Nonviolent physical risk-taking enhances conceptualized formidability |url=https://linkinghub.elsevier.com/retrieve/pii/S1090513813000950 |journal=Evolution and Human Behavior |language=en |volume=35 |issue=1 |pages=26–33 |doi=10.1016/j.evolhumbehav.2013.09.003|s2cid=9657298 }}</ref> Status badges such as facial hair are generally related to men being perceived as more dominant.<ref name=":3" /> Facial hair makes the jaw appear more prominent and shows emotions like anger clearly which makes a male appear more threatening.<ref>{{Cite journal |last1=Craig |first1=Belinda M. |last2=Nelson |first2=Nicole L. |last3=Dixson |first3=Barnaby J. W. |date=May 2019 |title=Sexual Selection, Agonistic Signaling, and the Effect of Beards on Recognition of Men's Anger Displays |url=http://journals.sagepub.com/doi/10.1177/0956797619834876 |journal=Psychological Science |language=en |volume=30 |issue=5 |pages=728–738 |doi=10.1177/0956797619834876 |pmid=30908116 |s2cid=85514733 |issn=0956-7976|doi-access=free }}</ref><ref>Guthrie, R. (1970). Evolution of human threat display organs. ''Evolutionary Biology, 4'', 257–302.</ref> Dominance has been associated with increased male mating success.<ref>{{Cite journal |last1=Hill |first1=Alexander K. |last2=Hunt |first2=John |last3=Welling |first3=Lisa L.M. |last4=Cárdenas |first4=Rodrigo A. |last5=Rotella |first5=Michelle A. |last6=Wheatley |first6=John R. |last7=Dawood |first7=Khytam |last8=Shriver |first8=Mark D. |last9=Puts |first9=David A. |date=September 2013 |title=Quantifying the strength and form of sexual selection on men's traits |url=https://linkinghub.elsevier.com/retrieve/pii/S1090513813000615 |journal=Evolution and Human Behavior |language=en |volume=34 |issue=5 |pages=334–341 |doi=10.1016/j.evolhumbehav.2013.05.004}}</ref><ref>{{Cite journal |last1=Kordsmeyer |first1=Tobias L. |last2=Hunt |first2=John |last3=Puts |first3=David A. |last4=Ostner |first4=Julia |last5=Penke |first5=Lars |date=July 2018 |title=The relative importance of intra- and intersexual selection on human male sexually dimorphic traits |url=https://linkinghub.elsevier.com/retrieve/pii/S1090513817304105 |journal=Evolution and Human Behavior |language=en |volume=39 |issue=4 |pages=424–436 |doi=10.1016/j.evolhumbehav.2018.03.008|s2cid=150154211 }}</ref><ref>Wolff, S. E., & Puts, D. A. (2010). "Vocal masculinity is a robust dominance signal in men". ''Behavioral Ecology and Sociobiology, 64''(10), 1673–1683. {{doi|10.1007/s00265-010-0981-5}}</ref>

Often contest competition produces anatomical weapons such as antlers or large canine teeth; however, hominids lack canine weaponry typical of other primates.<ref name=":3" /> Reduced canine size may be due to bipedalism and adaptations of the hand.<ref name=":5">{{Cite journal |last=Carrier |first=David R. |date=2011-05-18 |title=The Advantage of Standing Up to Fight and the Evolution of Habitual Bipedalism in Hominins |journal=PLOS ONE |volume=6 |issue=5 |pages=e19630 |doi=10.1371/journal.pone.0019630 |pmid=21611167 |pmc=3097185 |bibcode=2011PLoSO...619630C |issn=1932-6203|doi-access=free }}</ref><ref>{{Cite book |last=Darwin |first=Charles |url=http://dx.doi.org/10.5962/bhl.title.2092 |title=The descent of man, and selection in relation to sex |date=1871 |publisher=J. Murray |location=London|doi=10.5962/bhl.title.2092 }}</ref> Bipedalism is not a common trait, yet many species like the great apes stand on their hind legs when fighting, which increases power behind blows.<ref>{{Cite journal |last1=Thorpe |first1=S.K.S. |last2=Crompton |first2=R.H. |last3=Wang |first3=W.J. |date=2004-02-08 |title=Stresses Exerted in the Hindlimb Muscles of Common Chimpanzees (Pan troglodytes) during Bipedal Locomotion |url=http://dx.doi.org/10.1159/000078937 |journal=Folia Primatologica |volume=75 |issue=4 |pages=253–265 |doi=10.1159/000078937 |pmid=15316153 |s2cid=20869474 |issn=0015-5713}}</ref><ref name=":3" /> Hominin hands are adapted for gripping tools or hurling objects like stones.<ref>{{Cite journal |last1=Marzke |first1=M. W. |last2=Wullstein |first2=K. L. |last3=Viegas |first3=S. F. |date=November 1992 |title=Evolution of the power ("squeeze") grip and its morphological correlates in hominids |url=https://onlinelibrary.wiley.com/doi/10.1002/ajpa.1330890303 |journal=American Journal of Physical Anthropology |language=en |volume=89 |issue=3 |pages=283–298 |doi=10.1002/ajpa.1330890303 |pmid=1485637 |issn=0002-9483}}</ref><ref>{{Cite journal |last=Napier |first=John|date=November 1962 |title=Fossil Hand Bones from Olduvai Gorge |url=http://dx.doi.org/10.1038/196409a0 |journal=Nature |volume=196 |issue=4853 |pages=409–411 |doi=10.1038/196409a0 |bibcode=1962Natur.196..409N |issn=0028-0836}}</ref><ref name=":6">{{Cite journal |last=Young |first=Richard W. |date=January 2003 |title=Evolution of the human hand: the role of throwing and clubbing |journal=Journal of Anatomy |language=en |volume=202 |issue=1 |pages=165–174 |doi=10.1046/j.1469-7580.2003.00144.x |pmid=12587931 |pmc=1571064 |issn=0021-8782}}</ref><ref>{{Cite journal |last=Young |first=Richard W. |date=2009-03-18 |title=The ontogeny of throwing and striking |url=https://onlinelibrary.wiley.com/doi/10.1002/huon.200800013 |journal=Human_ontogenetics |language=en |volume=3 |issue=1 |pages=19–31 |doi=10.1002/huon.200800013|doi-access=free }}</ref> Bipedalism and utilizing handheld objects such as weapons may have aided early hominins in contest competition, reducing sexual selection pressures of maintaining large canine teeth.<ref name=":5" /><ref name=":6" /><ref>{{Cite journal |last1=Plavcan |first1=J.Michael |last2=van Schaik |first2=Carel P. |date=April 1997 |title=Interpreting hominid behavior on the basis of sexual dimorphism |url=http://dx.doi.org/10.1006/jhev.1996.0096 |journal=Journal of Human Evolution |volume=32 |issue=4 |pages=345–374 |doi=10.1006/jhev.1996.0096 |pmid=9085186 |issn=0047-2484}}</ref>

Several other traits in human males may have been selected for contest competition. Males exhibit a more robust face compared to females.<ref name=":3" /> This may have provided protection against blows to the face during contest competitions as the areas on the skull that have increased robusticity are parts that are more likely to suffer from injury.<ref>{{Cite journal |last1=Carrier |first1=David R. |last2=Morgan |first2=Michael H. |date=February 2015 |title=Protective buttressing of the hominin face: Buttressing of the hominin face |url=https://onlinelibrary.wiley.com/doi/10.1111/brv.12112 |journal=Biological Reviews |language=en |volume=90 |issue=1 |pages=330–346 |doi=10.1111/brv.12112|pmid=24909544 |s2cid=14777701 }}</ref>  Additionally, there are 23% more lefthanded males than females.<ref>{{Cite journal |last1=Papadatou-Pastou |first1=Marietta |last2=Martin |first2=Maryanne |last3=Munafò |first3=Marcus R. |last4=Jones |first4=Gregory V. |date=September 2008 |title=Sex differences in left-handedness: A meta-analysis of 144 studies. |url=http://dx.doi.org/10.1037/a0012814 |journal=Psychological Bulletin |volume=134 |issue=5 |pages=677–699 |doi=10.1037/a0012814 |pmid=18729568 |issn=1939-1455}}</ref> Although left-handedness is heritable and associated with survival disadvantages, the rarity of left-handedness may have given ancestral males a fighting advantage in competitions keeping this trait in the gene pool via negative frequency-dependent selection.<ref name=":3" /><ref>{{Cite journal |last1=Medland |first1=Sarah E. |last2=Duffy |first2=David L. |last3=Wright |first3=Margaret J. |last4=Geffen |first4=Gina M. |last5=Hay |first5=David A. |last6=Levy |first6=Florence |last7=van-Beijsterveldt |first7=Catherina E.M. |last8=Willemsen |first8=Gonneke |last9=Townsend |first9=Grant C. |last10=White |first10=Vicki |last11=Hewitt |first11=Alex W. |last12=Mackey |first12=David A. |last13=Bailey |first13=J. Michael |last14=Slutske |first14=Wendy S. |last15=Nyholt |first15=Dale R. |date=January 2009 |title=Genetic influences on handedness: Data from 25,732 Australian and Dutch twin families |url=http://dx.doi.org/10.1016/j.neuropsychologia.2008.09.005 |journal=Neuropsychologia |volume=47 |issue=2 |pages=330–337 |doi=10.1016/j.neuropsychologia.2008.09.005 |pmid=18824185 |pmc=2755095 |issn=0028-3932}}</ref><ref>{{Cite journal |last1=Coren |first1=Stanley |last2=Halpern |first2=Diane F. |date=1991 |title=Left-handedness: A marker for decreased survival fitness. |url=http://dx.doi.org/10.1037/0033-2909.109.1.90 |journal=Psychological Bulletin |volume=109 |issue=1 |pages=90–106 |doi=10.1037/0033-2909.109.1.90 |pmid=2006231 |issn=1939-1455}}</ref><ref>{{Cite journal |date=1996-12-22 |title=Frequency-dependent maintenance of left handedness in humans |url=http://dx.doi.org/10.1098/rspb.1996.0238 |journal=Proceedings of the Royal Society of London. Series B: Biological Sciences |volume=263 |issue=1377 |pages=1627–1633 |doi=10.1098/rspb.1996.0238 |pmid=9025310 |issn=0962-8452|last1=Raymond |first1=M. |last2=Pontier |first2=D. |last3=Dufour |first3=A. B. |last4=Møller |first4=A. P. |s2cid=11938077 }}</ref> Many combat sports such as boxing have higher-than-chance frequencies of left-handed individuals among the top competitors.<ref>{{Cite journal |last1=Richardson |first1=Thomas |last2=Gilman |first2=R. Tucker |date=2019-02-21 |title=Left-handedness is associated with greater fighting success in humans |url=http://dx.doi.org/10.1101/555912 |access-date=2022-12-12 |journal=Scientific Reports|volume=9 |issue=1 |page=15402 |doi=10.1038/s41598-019-51975-3|biorxiv=10.1101/555912 |pmid=31659217 |pmc=6817864 |bibcode=2019NatSR...915402R }}</ref> Human males are also able to tolerate pain longer than females, especially during competition.<ref name=":3" /><ref>Fillingim, R. B., King, C. D., Ribeiro-Dasilva, M. C., Rahim-Williams, B., & Riley, J. L. (2009). Sex, gender, and pain: a review of recent clinical and experimental findings. ''The journal of pain'', 10(5), 447–485. Fitch, W. T., & Giedd, J. (1999).</ref><ref>{{Cite journal |last1=Riley |first1=Joseph L |last2=Robinson |first2=Michael E |last3=Wise |first3=Emily A |last4=Myers |first4=Cynthia D |last5=Fillingim |first5=Roger B |date=January 1998 |title=Sex differences in the perception of noxious experimental stimuli: a meta-analysis |url=http://dx.doi.org/10.1016/s0304-3959(97)00199-1 |journal=Pain |volume=74 |issue=2 |pages=181–187 |doi=10.1016/s0304-3959(97)00199-1 |pmid=9520232 |s2cid=9189089 |issn=0304-3959}}</ref>  A higher pain tolerance allows for males to remain aggressive during contests along with an increased aerobic capacity.<ref name=":3" /> Males have an oxygen capacity rate that is 25–30% higher than females.<ref>{{Cite journal |last1=Billat |first1=Véronique L. |last2=Demarle |first2=Alexandre|last3=Slawinski|first3=Jean|last4=Paiva |first4=Mario|last5=Koralsztein |first5=Jean-Pierre|date=December 2001 |title=Physical and training characteristics of top-class marathon runners |journal=Medicine & Science in Sports & Exercise |volume=33 |issue=12 |pages=2089–2097 |doi=10.1097/00005768-200112000-00018 |pmid=11740304 |s2cid=38838193 |issn=0195-9131|doi-access=free }}</ref><ref>{{Cite journal |last1=Davies |first1=C. T. M. |last2=Thompson |first2=M. W. |date=August 1979 |title=Aerobic performance of female marathon and male ultramarathon athletes |url=http://dx.doi.org/10.1007/bf00429740 |journal=European Journal of Applied Physiology and Occupational Physiology |volume=41 |issue=4 |pages=233–245 |doi=10.1007/bf00429740 |pmid=499187 |s2cid=39782050 |issn=0301-5548}}</ref> This aerobic capacity increases during puberty when males are sexually maturing and preparing to mate.<ref name=":3" />

Human males engage in both within-group contest competition and coalitional aggression.<ref name=":3" /> The latter form competition may be supported by males tending to contribute more to a group task when competing against other groups and to discriminate more strongly against outgroup members.<ref>{{Cite journal |last1=Vugt |first1=Mark Van |last2=Cremer |first2=David De |last3=Janssen |first3=Dirk P. |date=January 2007 |title=Gender Differences in Cooperation and Competition |url=http://dx.doi.org/10.1111/j.1467-9280.2007.01842.x |journal=Psychological Science |volume=18 |issue=1 |pages=19–23 |doi=10.1111/j.1467-9280.2007.01842.x |pmid=17362372 |s2cid=3566509 |issn=0956-7976}}</ref><ref>{{Cite journal |last1=Brooks |first1=James |last2=Onishi |first2=Ena |last3=Clark |first3=Isabelle R. |last4=Bohn |first4=Manuel |last5=Yamamoto |first5=Shinya |date=2021-02-24 |title=Uniting against a common enemy: Perceived outgroup threat elicits ingroup cohesion in chimpanzees |journal=PLOS ONE |volume=16 |issue=2 |pages=e0246869 |doi=10.1371/journal.pone.0246869 |pmid=33626062 |pmc=7904213 |bibcode=2021PLoSO..1646869B |issn=1932-6203|doi-access=free }}</ref><ref>{{Cite journal |last1=McDonald |first1=Melissa M. |last2=Navarrete |first2=Carlos David |last3=Van Vugt |first3=Mark |date=2012-03-05 |title=Evolution and the psychology of intergroup conflict: the male warrior hypothesis |url=http://dx.doi.org/10.1098/rstb.2011.0301 |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=367 |issue=1589 |pages=670–679 |doi=10.1098/rstb.2011.0301 |pmid=22271783 |pmc=3260849 |issn=0962-8436}}</ref><ref>{{Cite journal |last=Wrangham |first=Richard W. |date=1999 |title=Evolution of coalitionary killing |journal=American Journal of Physical Anthropology |volume=110 |issue=S29 |pages=1–30 |doi=10.1002/(sici)1096-8644(1999)110:29+<1::aid-ajpa2>3.0.co;2-e |issn=0002-9483|doi-access=free }}</ref>

Traits that evolve during contest competition, such as large body size and physical aggression, are often costly to produce and maintain.<ref name=":7">{{Cite journal |last1=Berglund |first1=Anders |last2=Bisazza |first2=Angelo |last3=Pilastro |first3=Andrea |date=August 1996 |title=Armaments and ornaments: an evolutionary explanation of traits of dual utility |journal=Biological Journal of the Linnean Society |volume=58 |issue=4 |pages=385–399 |doi=10.1111/j.1095-8312.1996.tb01442.x |issn=0024-4066|doi-access=free }}</ref> These traits may therefore be indicators of male genetic quality and/or ability to provide resources and other direct benefits.<ref name=":7" /> Consequently, human females may evolve preferences for these traits, which then comprise an additional selection pressure.  However, secondary sexual characteristics in human males do not always enhance overall [[Social:Physical attractiveness|attractiveness]] to females.<ref>{{Cite journal |last=Puts |first=David A. |date=May 2010 |title=Beauty and the beast: mechanisms of sexual selection in humans |url=http://dx.doi.org/10.1016/j.evolhumbehav.2010.02.005 |journal=Evolution and Human Behavior |volume=31 |issue=3 |pages=157–175 |doi=10.1016/j.evolhumbehav.2010.02.005 |issn=1090-5138}}</ref><ref>{{Cite journal |last1=Frederick |first1=David A. |last2=Haselton |first2=Martie G. |date=August 2007 |title=Why Is Muscularity Sexy? Tests of the Fitness Indicator Hypothesis |url=http://journals.sagepub.com/doi/10.1177/0146167207303022 |journal=Personality and Social Psychology Bulletin |language=en |volume=33 |issue=8 |pages=1167–1183 |doi=10.1177/0146167207303022 |pmid=17578932 |s2cid=2972841 |issn=0146-1672}}</ref><ref>{{Cite journal |last1=Puts |first1=David A. |last2=Jones |first2=Benedict C. |last3=DeBruine |first3=Lisa M. |date=2012-03-01 |title=Sexual Selection on Human Faces and Voices |url=https://www.tandfonline.com/doi/full/10.1080/00224499.2012.658924 |journal=The Journal of Sex Research |language=en |volume=49 |issue=2–3 |pages=227–243 |doi=10.1080/00224499.2012.658924 |pmid=22380590 |s2cid=27040803 |issn=0022-4499}}</ref> Some traits of human males that function in contests, such as body size, strength, and weaponry usage, may also have been selected to aid in hunting.<ref name=":3" /> However, contest competition is observed in all great apes and thus likely preceded hunting as a selective pressure.<ref name=":3" />

== Sexual selection in females ==

Human female mating competition is complex and multifaceted and varies across cultures, societies, and individuals.<ref>{{cite journal |last1=Buss |first1=David M. |title=Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures |journal=Behavioral and Brain Sciences |date=March 1989 |volume=12 |issue=1 |pages=1–14 |doi=10.1017/S0140525X00023992|s2cid=3807679 |doi-access=free }}</ref> Females may compete for high-quality mates who possess traits that indicate underlying genetic quality, possibly including physical attractiveness and intelligence,<ref name="Female Intrasexual Competition">{{cite journal |last1=Fisher |first1=Maryanne L. |title=Female Intrasexual Competition |journal=The Cambridge Handbook of Evolutionary Perspectives on Sexual Psychology: Volume 3: Female Sexual Adaptations |date=2022 |volume=3 |pages=91–117 |doi=10.1017/9781108943567.006|isbn=9781108943567 }}</ref> or material resources that can enhance the survival and reproductive success of the female and her offspring.<ref>{{cite journal |last1=Campbell |first1=Anne |title=Staying alive: Evolution, culture, and women's intrasexual aggression |journal=Behavioral and Brain Sciences |date=April 1999 |volume=22 |issue=2 |pages=203–214 |doi=10.1017/s0140525x99001818|pmid=11301523 |s2cid=1081104 }}</ref><ref name="Female Intrasexual Competition"/>

Females may also compete for leadership and reputation in social alliances and networks that can provide support, protection, and mating opportunities.<ref name="Self-protection as an adaptive fema">{{cite journal |last1=Benenson |first1=Joyce F. |last2=Webb |first2=Christine E. |last3=Wrangham |first3=Richard W. |title=Self-protection as an adaptive female strategy |journal=Behavioral and Brain Sciences |date=2022 |volume=45 |pages=e128 |doi=10.1017/S0140525X21002417|pmid=34742359 |s2cid=243845886 }}</ref><ref name="An Evolutionary Review of Female In">{{cite journal |last1=Fisher |first1=Maryanne L. |last2=Krems |first2=Jaimie Arona |title=An Evolutionary Review of Female Intrasexual Competition |journal=The Oxford Handbook of Human Mating |date=26 January 2023 |pages=378–C14.P201 |doi=10.1093/oxfordhb/9780197536438.013.27|isbn=978-0197536438 }}</ref> Human females compete with other females, sometimes including co-wives, to obtain and retain investment from mates, while managing cooperative same-sex relationships.<ref>{{cite journal |last1=Benenson |first1=Joyce F. |title=Dominating versus eliminating the competition: Sex differences in human intrasexual aggression |journal=Behavioral and Brain Sciences |date=August 2009 |volume=32 |issue=3–4 |pages=268–269 |doi=10.1017/s0140525x0999046x}}</ref>

=== Female mate competition ===

Over human evolution, the cost of aggressive and physical contests in females may have been high given that females were the primary caregivers and protectors of offspring, so a mother's death greatly impacts infant mortality.<ref name="Self-protection as an adaptive fema"/><ref name="An Evolutionary Review of Female In"/> Some behaviors from mothers competing with other females at a similar life stage over resources include self-promotion and competitor derogation.<ref name="An Evolutionary Review of Female In"/> However, maternal competition remains understudied.  
Compared to male aggression, female aggression tends to be more indirect. Females tend to engage in more subtle and indirect aggression, such as gossip, as a competitive tool to harm same-sex rivals' social opportunities<ref>{{cite journal |last1=Campbell |first1=Anne |title=The evolutionary psychology of women's aggression |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=5 December 2013 |volume=368 |issue=1631 |pages=20130078 |doi=10.1098/rstb.2013.0078|pmid=24167308 |pmc=3826207 }}</ref> and partake in competitor derogation to prevent female rivals from getting male attention.<ref name="An Evolutionary Review of Female In"/> Gossip, derogation, and social exclusion grant the aggressor the chance to go undetected and avoid retaliation. Derogation, for example, can eliminate same-sex rivals by reducing their ability to compete; it was found that girls' suicide attempts were associated with any amount of indirect peer victimization, whereas only frequent indirect peer victimization was associated with boys' suicide attempts.<ref name="An Evolutionary Review of Female In"/> Furthermore, same-sex harassment in some nonhuman animals impacted females' ovulation capabilities, which suggests that human females' reproductive success could be influenced by the stress induced by indirect or direct peer victimization.<ref name="An Evolutionary Review of Female In"/>  
Males pursue both sexually attractive and faithful long-term partners, which might be the source of female mating competition greatly revolving around denigrating same-sex rivals' attractiveness and reputation through accusations of promiscuity and infidelity.<ref name="An Evolutionary Review of Female In"/> Competitive women are more likely to spread reputation-harming information about other women, suggesting that reputation manipulation is a form of female competition for romantic partners.<ref>{{cite journal |doi=10.1016/j.jesp.2018.03.011 |title=Competitive reputation manipulation: Women strategically transmit social information about romantic rivals |year=2018 |last1=Reynolds |first1=Tania |last2=Baumeister |first2=Roy F. |last3=Maner |first3=Jon K. |journal=Journal of Experimental Social Psychology |volume=78 |pages=195–209 |s2cid=146804099 }}</ref> 
Women are more likely to compete for desirable mates when maternal investment levels are high, and their social groups are largely composed of mothers,<ref>{{cite journal |last1=Rosvall |first1=Kimberly A. |title=Intrasexual competition in females: evidence for sexual selection? |journal=Behavioral Ecology |date=1 November 2011 |volume=22 |issue=6 |pages=1131–1140 |doi=10.1093/beheco/arr106|pmid=22479137 |pmc=3199163 }}</ref> as more women living closer together are looking for similar resources that benefit their own survival and that of their children.<ref name="An Evolutionary Review of Female In"/>

=== Sexually selected female traits ===

Competition for mates among human females may take multiple forms. Contests tend to be less frequent, aggressive, and injurious than male-male contests.<ref>{{Cite journal |last=Campbell |first=Anne |date=2013-12-05 |title=The evolutionary psychology of women's aggression |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=368 |issue=1631 |pages=20130078 |doi=10.1098/rstb.2013.0078 |pmid=24167308 |pmc=3826207 |issn=0962-8436}}</ref> This leads to a difference in the traits selected. The indirect aggression in which females engage can take the form of damaging the reputation of other women (e.g., via gossip), potentially influencing their sexual behavior and opportunities.<ref name="Fisher 378–C14.P201">{{Citation |last1=Fisher |first1=Maryanne L. |title=An Evolutionary Review of Female Intrasexual Competition |date=2023-01-26 |url=http://dx.doi.org/10.1093/oxfordhb/9780197536438.013.27 |work=The Oxford Handbook of Human Mating |pages=378–C14.P201 |access-date=2023-12-09 |publisher=Oxford University Press |isbn=978-0-19-753643-8 |last2=Krems |first2=Jaimie Arona|doi=10.1093/oxfordhb/9780197536438.013.27 }}</ref> Additionally, females compete with one another through male mate choice, e.g., by enhancing their own physical attractiveness.<ref name="Fisher 378–C14.P201"/> Some female anatomical traits are targets of male mate choice and possibly represent female sexual ornaments shaped by selection. Femininity in the female face and voice provide cues to female reproductive hormones and reproductive potential.<ref>{{Cite journal |last1=Moore |first1=F.R. |last2=Law Smith |first2=M.J. |last3=Taylor |first3=V. |last4=Perrett |first4=D.I. |date=May 2011 |title=Sexual dimorphism in the female face is a cue to health and social status but not age |url=https://linkinghub.elsevier.com/retrieve/pii/S019188691100047X |journal=Personality and Individual Differences |language=en |volume=50 |issue=7 |pages=1068–1073 |doi=10.1016/j.paid.2011.01.026}}</ref> Males tend to have lower pitched voices than females, likely due to male intrasexual competition,<ref>{{Cite journal |last=Puts |first=David A. |date=May 2010 |title=Beauty and the beast: mechanisms of sexual selection in humans |url=https://linkinghub.elsevier.com/retrieve/pii/S1090513810000279 |journal=Evolution and Human Behavior |language=en |volume=31 |issue=3 |pages=157–175 |doi=10.1016/j.evolhumbehav.2010.02.005}}</ref> but some evidence suggests that high female voice pitch may also be favored by male mate choice and function in intrasexual competition among females.<ref>{{Cite journal |last1=Puts |first1=David A. |last2=Jones |first2=Benedict C. |last3=DeBruine |first3=Lisa M. |date=2012-03-01 |title=Sexual Selection on Human Faces and Voices |url=https://www.tandfonline.com/doi/full/10.1080/00224499.2012.658924 |journal=The Journal of Sex Research |language=en |volume=49 |issue=2–3 |pages=227–243 |doi=10.1080/00224499.2012.658924 |pmid=22380590 |s2cid=27040803 |issn=0022-4499}}</ref>

Deposition of fat on the hips, buttocks, and breasts in human females may also be an outcome of female sexual selection, signaling the ability to support gestation and lactation for offspring in environments where resources may be low.<ref name=":8">{{Cite journal |last=Dixson |first=Barnaby J. W. |date=January 2022 |title=Sexual Selection and the Evolution of Human Appearance Enhancements |url=https://link.springer.com/10.1007/s10508-021-01946-5 |journal=Archives of Sexual Behavior |language=en |volume=51 |issue=1 |pages=49–55 |doi=10.1007/s10508-021-01946-5 |pmid=33721143 |s2cid=232244631 |issn=0004-0002}}</ref><ref>{{Cite journal |last=Norgan |first=Ng |date=September 1997 |title=The beneficial effects of body fat and adipose tissue in humans* |url=https://www.nature.com/articles/0800473 |journal=International Journal of Obesity |language=en |volume=21 |issue=9 |pages=738–746 |doi=10.1038/sj.ijo.0800473 |pmid=9376885 |s2cid=5781207 |issn=0307-0565}}</ref> However, in the Western World, women with larger breasts are seen as more likely to commit infidelity and more likely to participate in intra-sexual competition with other females.<ref name=":8" /> Greater overall body fat percentage in human females appears to be unique among primates and may function in storing resources needed to gestate and support large-brained offspring<ref>{{Cite journal |last1=Lassek |first1=W |last2=Gaulin |first2=S |date=January 2008 |title=Waist-hip ratio and cognitive ability: is gluteofemoral fat a privileged store of neurodevelopmental resources? |url=https://linkinghub.elsevier.com/retrieve/pii/S1090513807000736 |journal=Evolution and Human Behavior |language=en |volume=29 |issue=1 |pages=26–34 |doi=10.1016/j.evolhumbehav.2007.07.005}}</ref> as well as in sexual selection.<ref>{{Cite journal |last=Singh |first=Devendra |date=1993 |title=Adaptive significance of female physical attractiveness: Role of waist-to-hip ratio. |url=http://doi.apa.org/getdoi.cfm?doi=10.1037/0022-3514.65.2.293 |journal=Journal of Personality and Social Psychology |language=en |volume=65 |issue=2 |pages=293–307 |doi=10.1037/0022-3514.65.2.293 |pmid=8366421 |issn=1939-1315}}</ref> For example, higher female body mass index (BMI) is associated with increased fertility in young women, particularly those in subsistence societies.<ref>{{Cite journal |last1=Hochberg |first1=Ze'ev |last2=Gawlik |first2=Aneta |last3=Walker |first3=Robert S |date=December 2011 |title=Evolutionary fitness as a function of pubertal age in 22 subsistence-based traditional societies |journal=International Journal of Pediatric Endocrinology |language=en |volume=2011 |issue=1 |page=2 |doi=10.1186/1687-9856-2011-2 |issn=1687-9856 |pmc=3159136 |pmid=21860629 |doi-access=free }}</ref> Lower WHR, lower BMI, and smaller waist sizes are also associated with lower birth weights and higher infant mortality.<ref>{{Cite journal |last1=Lassek |first1=William D. |last2=Gaulin |first2=Steven J. C. |date=2018-10-01 |title=Do the Low WHRs and BMIs Judged Most Attractive Indicate Higher Fertility? |journal=Evolutionary Psychology |language=en |volume=16 |issue=4 |pages=147470491880006 |doi=10.1177/1474704918800063 |pmid=30296846 |pmc=10480809 |s2cid=52941981 |issn=1474-7049}}</ref> Such traits, particularly body fat distribution, may represent sexual ornamentation, which is important in mating throughout the animal kingdom, for example, in birds.<ref>{{Cite journal |last1=Mahoney |first1=Sean M. |last2=Reudink |first2=Matthew W. |last3=Contina |first3=Andrea |last4=Roberts |first4=Kelly A. |last5=Schabert |first5=Veronica T. |last6=Gunther |first6=Emily G. |last7=Covino |first7=Kristen M. |date=March 2022 |title=A tail of plumage colouration: disentangling geographic, seasonal and dietary effects on plumage colour in a migratory songbird |url=https://onlinelibrary.wiley.com/doi/10.1111/jav.02957 |journal=Journal of Avian Biology |language=en |volume=2022 |issue=3 |doi=10.1111/jav.02957 |issn=0908-8857|doi-access=free }}</ref><ref>{{Cite journal |last1=Loyau |first1=Adeline |last2=Jalme |first2=Michel Saint |last3=Sorci |first3=Gabriele |date=September 2005 |title=Intra‐ and Intersexual Selection for Multiple Traits in the Peacock ( Pavo cristatus ) |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.2005.01091.x |journal=Ethology |language=en |volume=111 |issue=9 |pages=810–820 |doi=10.1111/j.1439-0310.2005.01091.x |bibcode=2005Ethol.111..810L |issn=0179-1613}}</ref> Humans also use bodily decoration, including jewelry, tattoos, scarification, and makeup to enhance appearance and desirability to potential mates.<ref name=":8" /><ref>{{Cite journal |last1=Carmen |first1=Rachael A. |last2=Guitar |first2=Amanda E. |last3=Dillon |first3=Haley M. |date=June 2012 |title=Ultimate Answers to Proximate Questions: The Evolutionary Motivations behind Tattoos and Body Piercings in Popular Culture |url=http://journals.sagepub.com/doi/10.1037/a0027908 |journal=Review of General Psychology |language=en |volume=16 |issue=2 |pages=134–143 |doi=10.1037/a0027908 |s2cid=8078573 |issn=1089-2680}}</ref>

In some non-human primates, red coloration may act as a sexual signal.<ref name=":9">{{Cite journal |last1=Elliot |first1=Andrew J. |last2=Pazda |first2=Adam D. |date=2012-04-13 |editor-last=Clifton |editor-first=Julian |title=Dressed for Sex: Red as a Female Sexual Signal in Humans |journal=PLOS ONE |language=en |volume=7 |issue=4 |pages=e34607 |doi=10.1371/journal.pone.0034607 |issn=1932-6203 |pmc=3326027 |pmid=22514643 |bibcode=2012PLoSO...734607E |doi-access=free }}</ref><ref>{{Cite journal |last1=Dubuc |first1=Constance |last2=Winters |first2=Sandra |last3=Allen |first3=William L. |last4=Brent |first4=Lauren J. N. |last5=Cascio |first5=Julie |last6=Maestripieri |first6=Dario |last7=Ruiz-Lambides |first7=Angelina V. |last8=Widdig |first8=Anja |last9=Higham |first9=James P. |date=2014-11-07 |title=Sexually selected skin colour is heritable and related to fecundity in a non-human primate |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=281 |issue=1794 |pages=20141602 |doi=10.1098/rspb.2014.1602 |pmid=25253459 |pmc=4211451 |issn=0962-8452}}</ref> For example, female mandrills have varying red facial colors that appear to indicate number of offspring and stage of ovulatory cycle, thereby advertising their apparent fertility.<ref>{{Cite journal |last1=Setchell |first1=Joanna M |last2=Jean Wickings |first2=E |last3=Knapp |first3=Leslie A |date=2006-09-22 |title=Signal content of red facial coloration in female mandrills ( Mandrillus sphinx ) |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=273 |issue=1599 |pages=2395–2400 |doi=10.1098/rspb.2006.3573 |pmid=16928644 |pmc=1636084 |issn=0962-8452}}</ref> Female rhesus macaques experience changes in facial redness during different times in their cycle, which is used by male macaques in mate choice, which is consistent with the proposal that this characteristic is sexually selected.<ref>{{Cite journal |last1=Higham |first1=James P |last2=Kimock |first2=Clare M |last3=Mandalaywala |first3=Tara M |last4=Heistermann |first4=Michael |last5=Cascio |first5=Julie |last6=Petersdorf |first6=Megan |last7=Winters |first7=Sandra |last8=Allen |first8=William L |last9=Dubuc |first9=Constance |date=2021-03-26 |editor-last=Barrett |editor-first=Louise |title=Female ornaments: is red skin color attractive to males and related to condition in rhesus macaques? |url=https://academic.oup.com/beheco/article/32/2/236/6122596 |journal=Behavioral Ecology |language=en |volume=32 |issue=2 |pages=236–247 |doi=10.1093/beheco/araa121 |issn=1045-2249 |pmc=7995641 |pmid=33814977}}</ref> Red has also been linked to human female sexuality.<ref name=":9" /> Some studies show that women who displayed themselves in red on dating websites were more likely to be interested in sex.<ref name=":9" /> Research has also shown that men perceive women in red as more sexually attractive than women who were not,<ref>{{Cite journal |last1=Elliot |first1=Andrew J. |last2=Niesta |first2=Daniela |date=2008 |title=Romantic red: Red enhances men's attraction to women. |url=http://doi.apa.org/getdoi.cfm?doi=10.1037/0022-3514.95.5.1150 |journal=Journal of Personality and Social Psychology |language=en |volume=95 |issue=5 |pages=1150–1164 |doi=10.1037/0022-3514.95.5.1150 |pmid=18954199 |issn=1939-1315}}</ref><ref>{{Cite journal |last1=Niesta Kayser |first1=Daniela |last2=Elliot |first2=Andrew J. |last3=Feltman |first3=Roger |date=October 2010 |title=Red and romantic behavior in men viewing women |url=https://onlinelibrary.wiley.com/doi/10.1002/ejsp.757 |journal=European Journal of Social Psychology |language=en |volume=40 |issue=6 |pages=901–908 |doi=10.1002/ejsp.757 |issn=0046-2772|doi-access=free }}</ref> particularly young, fertile women.<ref>{{Cite journal |last1=Schwarz |first1=Sascha |last2=Singer |first2=Marie |date=January 2013 |title=Romantic red revisited: Red enhances men's attraction to young, but not menopausal women |url=https://linkinghub.elsevier.com/retrieve/pii/S0022103112001564 |journal=Journal of Experimental Social Psychology |language=en |volume=49 |issue=1 |pages=161–164 |doi=10.1016/j.jesp.2012.08.004}}</ref>  

It has also been suggested that women who are nearing ovulation were more likely to be judged as more attractive than their counterparts who were in different stages of their cycle.<ref>{{Cite journal |last1=Haselton |first1=Martie G. |last2=Mortezaie |first2=Mina |last3=Pillsworth |first3=Elizabeth G. |last4=Bleske-Rechek |first4=April |last5=Frederick |first5=David A. |date=January 2007 |title=Ovulatory shifts in human female ornamentation: Near ovulation, women dress to impress |url=https://linkinghub.elsevier.com/retrieve/pii/S0018506X06002509 |journal=Hormones and Behavior |language=en |volume=51 |issue=1 |pages=40–45 |doi=10.1016/j.yhbeh.2006.07.007|pmid=17045994 |s2cid=9268718 }}</ref> Facial and vocal attractiveness have been observed to change with estradiol and progesterone in pattens consistent with fertility-related increases,<ref>{{Cite journal |last1=Puts |first1=David A. |last2=Bailey |first2=Drew H. |last3=Cárdenas |first3=Rodrigo A. |last4=Burriss |first4=Robert P. |last5=Welling |first5=Lisa L. M. |last6=Wheatley |first6=John R. |last7=Dawood |first7=Khytam |date=2013-01-01 |title=Women's attractiveness changes with estradiol and progesterone across the ovulatory cycle |url=https://www.sciencedirect.com/science/article/pii/S0018506X12002796 |journal=Hormones and Behavior |volume=63 |issue=1 |pages=13–19 |doi=10.1016/j.yhbeh.2012.11.007 |pmid=23159480 |s2cid=32877653 |issn=0018-506X}}</ref> although some data challenge this interpretation.<ref>{{Cite journal |last1=Catena |first1=Tikal M. |last2=Simmons |first2=Zachary L. |last3=Roney |first3=James R. |date=September 2019 |title=Do women's faces become more attractive near ovulation? |url=https://linkinghub.elsevier.com/retrieve/pii/S0018506X19301333 |journal=Hormones and Behavior |language=en |volume=115 |pages=104560 |doi=10.1016/j.yhbeh.2019.07.008|pmid=31310761 |s2cid=197421994 }}</ref> In general, ovulatory cycle changes are more subtle than in non-human primates, perhaps representing leakage of information on fertility and hormonal status rather than signals functioning to convey this information.<ref>{{Cite journal |last1=Gangestad |first1=Steven W |last2=Thornhill |first2=Randy |date=2008-05-07 |title=Human oestrus |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=275 |issue=1638 |pages=991–1000 |doi=10.1098/rspb.2007.1425 |issn=0962-8452 |pmc=2394562 |pmid=18252670}}</ref>  

==Phenotype==

Sexual selection has continued to be suggested as a possible explanation for geographical variation in appearance within the human species; in modern hypotheses, marriage practices are proposed as the main determinant of sexual selection. John Manning<ref name="manning2009">{{cite book | title = The Finger Ratio | author = Manning, John | isbn = 978-0571215409 | year = 2009 | publisher = Faber & Faber}}</ref> suggests that where [[Social:Polygyny|polygyny]] is common (e.g. as result of women emancipation), men face intense competition for wives and are more likely to be completely unsuccessful in reproducing, and the result is strong selection of males for traits which are adaptive for successful reproduction. He proposes a link to skin color through selection of males for testosterone-mediated traits which confer an ability to successfully compete for females. He suggests testosterone makes the human immune system less competent to resist [[Biology:Pathogen|pathogen]]s. In this view the antimicrobial properties of [[Chemistry:Melanin|melanin]] help mitigate the susceptibility to disease that polygyny induces by increasing testosteronization. According to this argument, the anti-infective qualities of melanin were more important than protection from ultraviolet light in the evolution of the darkest skin types. Manning asserts that skin color is more correlated with the occurrence of polygyny – explicable by it having an antimicrobial function – than the latitudinal gradient in intensity of ultraviolet radiation, and he points to the lack of very dark skin at equatorial latitudes of the [[Earth:New World|New World]] and the relatively light skin of Khoisan people in Africa.<ref name="manning2009" /><ref>{{Cite journal| doi = 10.1006/jtbi.2001.2331| pmid = 11419954| year = 2001| last1 = MacKintosh | first1 = J.| title = The antimicrobial properties of melanocytes, melanosomes and melanin and the evolution of black skin.| volume = 211| issue = 2| pages = 101–113| journal = Journal of Theoretical Biology | bibcode = 2001JThBi.211..101M}}</ref>

Research seems to contradict Manning's explanation about skin color. In 1978, [[Organization:NASA|NASA]] launched the [[Physics:Total Ozone Mapping Spectrometer|Total Ozone Mapping Spectrometer]], which was able to measure the ultraviolet radiation reaching Earth's surface. Jablonski and Chaplin took the spectrometer's global ultraviolet measurements and compared them with published data on skin color in indigenous populations from more than 50 countries. There was an unmistakable correlation: The weaker the ultraviolet light, the fairer the skin.<ref>{{cite news | date = 1 February 2001 | author = Kirchweger, Gina | title = The Biology of . . . Skin Color | work = Discover | access-date = 31 March 2015 | url = http://discovermagazine.com/2001/feb/featbiology/}}</ref> Rogers ''et al.'' (2004) performed an examination of the variation in MC1R nucleotide sequences for people of different ancestry and compared the sequences of chimpanzees and humans from various regions of the Earth. Rogers concluded that, at the time of the evolutionary separation of chimpanzees and humans, the common ancestors of all humans had light skin that was covered by dark hair. Additionally, our closest extant relative, the chimpanzee, has light skin covered by thick body hair.<ref name=rogers2004>{{cite journal |last1=Rogers |first1=Alan R.  |last2=Iltis |first2=David |last3=Wooding |first3=Stephen |year=2004 |title=Genetic Variation at the MC1R Locus and the Time since Loss of Human Body Hair |journal=Current Anthropology |volume=45 |pages=105–108 |doi=10.1086/381006 |s2cid=224795768 }}
</ref> Over time human hair disappeared to allow better heat dissipation through sweating<ref name=jablonski2000>{{cite journal|last1=Jablonski |first1=Nina G. |last2=Chaplin |first2=George |last3=Chaplin |pmid=10896812 |title=The evolution of human skin coloration |year=2000 |pages=57–106 |issue=1 |volume=39 |journal=Journal of Human Evolution |url=http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf |doi=10.1006/jhev.2000.0403 |url-status=dead |archive-url=https://web.archive.org/web/20030324212017/http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf |archive-date=24 March 2003 }}</ref> and the skin tone grew darker to increase the [[Biology:Stratum corneum|epidermal permeability barrier]]<ref name=Elias2010>{{cite journal |last1=Elias |first1=Peter M |last2=Menon  |first2=Gapinathan |last3=Wetzel |first3=Bruce J |last4=Williams |first4=John (Jack) W| journal=American Journal of Human Biology| pmid=20209486 |year=2010 |volume=22 | issue=4| pages=526–537| title=Barrier Requirements as the Evolutionary "Driver" of Epidermal Pigmentation in Humans| doi=10.1002/ajhb.21043 | pmc=3071612}}</ref> and protect from folate [[Medicine:Folate deficiency|depletion]] due to the increased exposure to sunlight.<ref name=pmid20445093>{{cite journal |last1=Jablonski |first1=N. G. |last2=Chaplin |first2=G. |title=Colloquium Paper: Human skin pigmentation as an adaptation to UV radiation |journal=Proceedings of the National Academy of Sciences |volume=107 |pages=8962–8968 |year=2010 |doi=10.1073/pnas.0914628107 |pmid=20445093 |pmc=3024016 |bibcode=2010PNAS..107.8962J |issue=Suppl 2|doi-access=free }}</ref> When humans started to migrate away from the tropics, there was less-intense [[Astronomy:Sunlight|sunlight]], partly due to clothing to protect against cold weather. Under these conditions there was less photodestruction of folate, and so the evolutionary pressure stopping lighter-skinned gene variants from surviving was reduced. In addition, lighter skin is able to generate more [[Chemistry:Vitamin D|vitamin D]] (cholecalciferol) than darker skin, so it would have represented a health benefit in reduced sunlight if there were limited sources of vitamin D.<ref name=jablonski2000 /> The genetic mutations leading to light skin may have experienced selective pressure due to the adoption of farming and settlement in northern latitudes.<ref name=pmid19481954>{{cite journal |last1=Juzeniene |first1=Asta |last2=Setlow |first2=Richard |last3=Porojnicu |first3=Alina |last4=Steindal |first4=Arnfinn Hykkerud |last5=Moan |first5=Johan |title=Development of different human skin colors: A review highlighting photobiological and photobiophysical aspects |journal=Journal of Photochemistry and Photobiology B: Biology |volume=96 |pages=93–100 |year=2009 |doi=10.1016/j.jphotobiol.2009.04.009 |pmid=19481954 |issue=2}}</ref>

Anthropologist Peter Frost has proposed that sexual selection was responsible for the evolution of pigmentary traits of women in [[Place:Northern Europe|Northern]] and Eastern European populations. He contends that the diversity of hair and eye color in Northeast European populations originated as a consequence of intense [[Philosophy:Female intrasexual competition|female intrasexual competition]], and is an adaptation for reproductive success in women.<ref name="jsecjournal.com">{{cite journal|author=Frost, P. |year=2008 |url=http://137.140.1.71/jsec/articles/volume2/issue4/NEEPSfrost.pdf |title=Sexual selection and human geographic variation |journal=Journal of Social, Evolutionary, and Cultural Psychology |volume=2 |issue=4 |pages=169–191 |doi=10.1037/h0099346 |url-status=dead |archive-url=https://web.archive.org/web/20120425153306/http://137.140.1.71/jsec/articles/volume2/issue4/NEEPSfrost.pdf |archive-date=25 April 2012 }}</ref><ref>{{cite journal | last1 = Cunningham | first1 = M.R. | last2 = Roberts | first2 = A.R. | last3 = Barbee | first3 = A.P. | last4 = Druen | first4 = P.B. | last5 = Wu | first5 = C-H. | year = 1995 | title = Their ideas of beauty are, on the whole, the same as ours": consistency and variability in the cross-cultural perception of female physical attractiveness | journal = Journal of Personality and Social Psychology | volume = 68 | issue = 2| pages = 261–279 | doi=10.1037/0022-3514.68.2.261}}</ref>

==Geoffrey Miller hypothesis==
[[File:Homo habilis - forensic facial reconstruction.png|thumb|upright|''Homo habilis'' – forensic facial reconstruction]]

[[Biography:Geoffrey Miller (psychologist)|Geoffrey Miller]], drawing on some of Darwin's largely neglected ideas about human behavior, has hypothesized that many human behaviors not clearly tied to survival benefits, such as humor, music, visual art, some forms of altruism, verbal creativity, or the fact that most humans have a far greater vocabulary than that which is required for survival, can nevertheless play a role.<ref>Geoffrey Miller, The Mating Mind, p.111; published 2001</ref> Miller (2000) has proposed that this apparent redundancy is due to individuals using vocabulary to demonstrate their intelligence, and consequently their "fitness", to potential mates. This has been tested experimentally, and it appears that males do make greater use of lower-frequency (more unusual) words when in a romantic mindset compared to a non-romantic mindset, suggesting that vocabulary is likely to be used as a sexual display (Rosenberg & Tunney, 2008). All these qualities are considered courtship adaptations that have been favored through sexual selection.<ref name=Klasios>{{cite web| last=Klasios, J. |date=2013 |url=http://psycnet.apa.org/journals/gpr/17/4/428/ |title=Cognitive traits as sexually selected fitness indicators |work=Review of General Psychology | volume=17 |pages=428–442 }}</ref>

Miller is critical of theories that imply that human culture arose as accidents or by-products of human evolution. He believes that human culture arose through sexual selection for creative traits. In that view, many human artifacts could be considered subject to sexual selection as part of the extended phenotype, for instance clothing that enhances sexually selected traits.<ref name="Miller G 2000">Miller G. (2000). ''The mating mind: how sexual choice shaped the evolution of human nature'', London, Heineman, {{ISBN|0434007412}} (also Doubleday, {{ISBN|0385495161}}).</ref> During human evolution, on at least two occasions, hominid brain size increased rapidly over a short period of time followed by a period of stasis. The first period of brain expansion occurred 2.5 million years ago, when ''[[Biology:Homo habilis|Homo habilis]]'' first began using stone tools. The second period occurred 500,000 years ago, with the emergence of [[Biology:Archaic humans|archaic ''Homo sapiens'']]. Miller argues that the rapid increases in brain size would have occurred by a [[Positive feedback|positive feedback]] loop resulting in a [[Biology:Fisherian runaway|Fisherian runaway]] selection for larger brains. Tor Nørretranders, in ''The Generous Man'' conjectures how intelligence, musicality, artistic and social skills, and language might have evolved as an example of the [[Biology:Handicap principle|handicap principle]], analogously with the peacock's tail, the standard example of that principle.

==Opposing arguments==
The role of sexual selection in human evolution has been considered controversial from the moment of publication of Darwin's book on sexual selection (1871). Among his vocal critics were some of Darwin's supporters, such as Alfred Wallace, a believer in [[Unsolved:Spiritualism|spiritualism]] and a [[Philosophy:Mind–body dualism|non-material origin]] of the human mind, who argued that animals and birds do not [[Philosophy:Mate choice|choose mates]] based on sexual selection, and that the artistic faculties in humans belong to their [[Philosophy:Spirituality|spiritual]] nature and therefore cannot be connected to natural selection, which only affects the animal nature.<ref name="Fisher 1915a"/> Darwin was accused of looking to the evolution of early human ancestors through the moral codes of the 19th century [[History:Victorian era|Victorian society]].

==See also==
* [[Philosophy:Human mating strategies|Human mating strategies]]
* [[Philosophy:Hypergamy|Hypergamy]]
* Marriage squeeze
* [[Philosophy:Parental investment#Parental investment in humans|Parental investment in humans]]
* [[Biology:Strategic pluralism|Strategic pluralism]]

==References==
{{Reflist}}

==Further reading==
* {{cite book|last=Buss|first=David M.|title=The Evolution of Desire: Strategies of Human Mating|title-link=The Evolution of Desire|publisher=Basic Books|year=2016|isbn=978-0465097760|edition=3rd|place=New York|orig-year=1994}}
* {{cite book|last=Miller|first=Geoffrey F.|title=The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature|place=New York|publisher=Doubleday|year=2000|edition=1st|isbn=978-0385495165|url-access=registration|url=https://archive.org/details/matingmind00geof}}

{{Human Evolution}}
{{sociobiology}}
{{evolution}}
{{Evolutionary psychology}}

{{DEFAULTSORT:Sexual Selection in Human Evolution}}
[[Category:Human evolution]]
[[Category:Evolutionary psychology]]

{{Sourceattribution|Sexual selection in humans}}