Editing Breast (section)

==Evolutionary development==
[[File:Mountain gorilla breast feeding.KMRA.jpg|thumb|[[Mountain gorilla]] breastfeeding an infant]]
Humans are the only mammals whose breasts become permanently enlarged after [[sexual maturity]] (known in humans as [[puberty]]). The reason for this evolutionary change is unknown.<ref name="DM">{{Cite web |last=Alex |first=Bridget |date=6 March 2019 |title=Scientists Still Stumped by the Evolution of Human Breasts |url=https://www.discovermagazine.com/planet-earth/scientists-still-stumped-by-the-evolution-of-human-breasts |url-status=live |archive-url=https://web.archive.org/web/20220204163722/https://www.discovermagazine.com/planet-earth/scientists-still-stumped-by-the-evolution-of-human-breasts |archive-date=4 February 2022 |access-date=4 February 2022 |website=[[Discover (magazine)|Discover]]}}</ref> Several hypotheses have been put forward:

A link has been proposed to processes for synthesizing the [[endogenous]] [[steroid hormone]] precursor [[dehydroepiandrosterone]] which takes place in fat rich regions of the body like the buttocks and breasts. These contributed to human brain development and played a part in increasing brain size.  Breast enlargement may for this purpose have occurred as early as ''[[Homo ergaster]]'' (1.7–1.4 [[myr|MYA]]).<ref name=":2" /> Other breast formation hypotheses may have then taken over as principal drivers.<ref>{{Cite journal|last1=LeBlanc|first1=Steven A.|last2=Barnes|first2=Ethne|date=July 1974|title=On the Adaptive Significance of the Female Breast|url=http://dx.doi.org/10.1086/282935|journal=The American Naturalist|volume=108|issue=962|pages=577–578|doi=10.1086/282935|bibcode=1974ANat..108..577L |s2cid=85243414|issn=0003-0147|access-date=24 November 2021|archive-date=4 March 2022|archive-url=https://web.archive.org/web/20220304004849/https://www.journals.uchicago.edu/doi/10.1086/282935|url-status=live|url-access=subscription}}</ref><ref name=":1">{{Cite journal|last1=Howard|first1=Beatrice A.|last2=Veltmaat|first2=Jacqueline M.|date=18 May 2013|title=Embryonic Mammary Gland Development; a Domain of Fundamental Research with High Relevance for Breast Cancer Research|journal=Journal of Mammary Gland Biology and Neoplasia|volume=18|issue=2|pages=89–91|doi=10.1007/s10911-013-9296-2|pmid=23686554|s2cid=1657065|issn=1083-3021|doi-access=free}}</ref><ref name=":2">{{Cite journal|last1=Pawłowski|first1=Bogusław|last2=Żelaźniewicz|first2=Agnieszka|date=2021|title=The evolution of perennially enlarged breasts in women: a critical review and a novel hypothesis|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/brv.12778|journal=Biological Reviews|language=en|volume=96|issue=6|pages=2794–2809|doi=10.1111/brv.12778|pmid=34254729|s2cid=235807642|issn=1469-185X|access-date=30 November 2021|archive-date=30 November 2021|archive-url=https://web.archive.org/web/20211130190318/https://onlinelibrary.wiley.com/doi/abs/10.1111/brv.12778|url-status=live|url-access=subscription}}</ref>

It has been suggested by zoologists Avishag and [[Amotz Zahavi]] that the size of the human breasts can be explained by the [[Handicap principle|handicap theory]] of [[sexual dimorphism]]. This would see the explanation for larger breasts as them being an [[Signalling theory|honest display]] of the women's health and ability to grow and carry them in her life. Prospective mates can then evaluate the genes of a potential mate for their ability to sustain her health even with the additional energy demanding burden she is carrying.<ref>Geoffrey Miller: ''The Sexual Evolution. Choice of partner and the emergence of the mind.'' Spectrum Academic Publishing House, 2009, {{ISBN|978-3-8274-2508-9}}</ref><ref name=":0">{{cite journal |last1=Pawłowski |first1=Bogusław |last2=Żelaźniewicz |first2=Agnieszka |date=13 July 2021 |title=The evolution of perennially enlarged breasts in women: a critical review and a novel hypothesis |journal=Biological Reviews |volume=96 |issue=6 |pages=2794–2809 |doi=10.1111/brv.12778 |pmid=34254729 |s2cid=235807642| issn=0006-3231 }}</ref>

The zoologist [[Desmond Morris]] describes a sociobiological approach in his science book ''[[The Naked Ape]]''. He suggests, by making comparisons with the other primates, that breasts evolved to replace swelling buttocks as a sex signal of ovulation. He notes how humans have, relatively speaking, large penises as well as large breasts. Furthermore, early humans adopted bipedalism and face-to-face coitus. He therefore suggested enlarged sexual signals helped maintain the bond between a mated male and female even though they performed different duties and therefore were separated for lengths of time.<ref>{{Cite web |last1=Dunbar |first1=Robin |last2=Saini |first2=Angela |last3=Garrod |first3=Ben |last4=Rutherford |first4=Adam |date=24 September 2017 |title=The Naked Ape at 50: 'Its central claim has surely stood the test of time ' |url=http://www.theguardian.com/science/2017/sep/24/the-naked-ape-at-50-desmond-morris-four-experts-assess-impact |url-status=live |archive-url=https://web.archive.org/web/20211116160057/https://www.theguardian.com/science/2017/sep/24/the-naked-ape-at-50-desmond-morris-four-experts-assess-impact |archive-date=16 November 2021 |access-date=24 November 2021 |website=The Guardian |language=en}}</ref><ref name=":0" /><ref>{{Cite web |last=Binns |first=Corey |date=5 August 2010 |title=Why Do Women Have Breasts? |url=https://www.livescience.com/32745-why-do-women-have-breasts.html |url-status=live |archive-url=https://web.archive.org/web/20211124171609/https://www.livescience.com/32745-why-do-women-have-breasts.html |archive-date=24 November 2021 |access-date=24 November 2021 |website=Live Science |language=en}}</ref>

A 2001 study proposed that the rounded shape of a woman's breast evolved to prevent the sucking infant offspring from suffocating while feeding at the teat; that is, because of the human infant's small jaw, which did not project from the face to reach the nipple, they might block the [[Nose|nostrils]] against the mother's breast if it were of a flatter form (compare with the [[common chimpanzee]]). Theoretically, as the human jaw receded into the face, the woman's body compensated with round breasts.<ref name="Bentley">{{cite journal |last = Bentley |first = Gillian R. |year = 2001 |title = The evolution of the human breast |journal = American Journal of Physical Anthropology |volume = 32 |issue = 38 |doi = 10.1002/ajpa.1033 |pages = 30–50 }}</ref>

[[Ashley Montagu]]e (1965) proposed that breasts came about as an adaptation for infant feeding for a different reason, as early human ancestors adopted bipedalism and the loss of body hair.  Human upright stance meant infants must be carried at the hip or shoulder instead of on the back as in the apes. This gives the infant less opportunity to find the nipple or the purchase to cling on to the mother's body hair.  The mobility of the nipple on a large breast in most human females gives the infant more ability to find it, grasp it and feed.<ref name=":1" />

Other suggestions include simply that permanent breasts attracted mates, that "pendulous" breasts gave infants something to cling to, or that permanent breasts shared the function of a [[Camel#Hump|camel's hump]], to store fat as an energy reserve.<ref name="DM"/>