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{{Short description|Idea that the menstural cycle synchronizes with those of other women in close proximity}}
'''Menstrual synchrony''', also called the '''McClintock effect''',<ref name=Gosline2007>{{cite web |url=http://www.scientificamerican.com/article.cfm?id=do-women-who-live-together-menstruate-together |title=Do Women Who Live Together Menstruate Together? |first=Anna |last=Gosline |date=December 7, 2007 |publisher=Scientific American |access-date=2 January 2012}}</ref> or the '''Wellesley effect''',<ref>{{cite book |last1=Sapolsky |first1=Robert M. |title=Behave : the biology of humans at our best and worst |date=2017 |location=New York, New York |isbn=9780735222786 |page=11}}</ref> is a contested process whereby women who begin living together in close proximity would experience their [[menstrual cycle]] onsets (the onset of [[menstruation]] or menses) becoming more synchronized together in time than when previously living apart. "For example, the distribution of onsets of seven female lifeguards was scattered at the beginning of the summer, but after 3 months spent together, the onset of all seven cycles fell within a 4-day period."<ref name=McClintock1971>{{Cite journal | doi = 10.1038/229244a0| title = Menstrual Synchrony and Suppression| journal = Nature| volume = 229| issue = 5282| pages = 244–5| year = 1971| last1 = McClintock | first1 = M. K. | pmid=4994256| bibcode = 1971Natur.229..244M| s2cid = 4267390}}</ref>
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[[Martha McClintock]]'s 1971 paper, published in ''[[Nature (journal)|Nature]]'', says that menstrual cycle synchronization happens when the menstrual cycle onsets of two or more women become closer together in time than they were several months earlier.<ref name=McClintock1971/>
After the initial studies, several papers were published reporting methodological flaws in studies reporting menstrual synchrony, including McClintock's study. In addition, other studies were published that failed to find synchrony. The proposed mechanisms have also received scientific criticism. Reviews in 2006 and 2013 concluded that menstrual synchrony likely does not exist.<ref name = Ziomkiewicz2006>{{cite journal |doi=10.1007/s12110-006-1004-0 |pmid=26181611 |title=Menstrual synchrony: Fact or artifact? |year=2006 |last1=Ziomkiewicz |first1=Anna |journal=Human Nature |volume=17 |issue=4 |pages=419–32|s2cid=40834364 }}</ref><ref name=Yang2006>{{cite journal |doi=10.1007/s12110-006-1005-z |pmid=26181612 |title=Women do not synchronize their menstrual cycles |year=2006 |last1=Yang |first1=Zhengwei |last2=Schank |first2=Jeffrey C. |journal=Human Nature |volume=17 |issue=4 |pages=433–47|s2cid=2316864 }}</ref><ref name=Schrank2006>{{cite journal |doi=10.1007/s12110-006-1006-y |title=Do human menstrual-cycle pheromones exist? |year=2006 |last1=Schrank |first1=Jeffrey C. |journal=Human Nature |volume=17 |issue=4 |pages=448–70 |pmid=26181613 |s2cid=14918247 }}</ref><ref name=Harris2013>{{cite journal |doi=10.1080/00224499.2012.763085 |title=Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning |year=2013 |last1=Harris |first1=Amy L. |last2=Vitzthum |first2=Virginia J. |journal=Journal of Sex Research |volume=50 |issue=3–4 |pages=207–46 |pmid=23480070|s2cid=30229421 }}</ref>
== Overview ==
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===Proposed causes===
McClintock hypothesized that [[pheromone]]s could cause menstrual cycle synchronization.<ref name=McClintock1971/><ref name=McClintock1998>{{cite journal |pmid=10349026 |year=1998 |last1=McClintock |first1=MK |title=Whither menstrual synchrony?|volume=9 |pages=77–95 |journal=Annual Review of Sex Research|doi=10.1080/10532528.1998.10559927 }}</ref> However, other mechanisms have been proposed, most prominently synchronization with [[lunar phases]].<ref name=Harris2013/>
===Efforts to replicate McClintock's results===
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After the initial studies reporting menstrual synchrony began to appear in the [[scientific literature]], other researchers began reporting the failure to find menstrual synchrony.<ref name =Wilson1991>{{cite journal |doi=10.1016/0306-4530(91)90021-K |title=Two studies of menstrual synchrony: Negative results |year=1991 |last1=Wilson |first1=H |last2=Kiefhaber |first2=S |last3=Gravel |first3=V |journal=Psychoneuroendocrinology |volume=16 |issue=4 |pages=353–9 |pmid=1745701|s2cid=23960204 }}</ref><ref name =Trevathan>{{cite journal |doi=10.1016/0306-4530(93)90017-F |title=No evidence for menstrual synchrony in lesbian couples |year=1993 |last1=Trevathan |first1=Wenda R. |last2=Burleson |first2=Mary H. |last3=Gregory |first3=W.Larry |journal=Psychoneuroendocrinology |volume=18 |issue=5–6 |pages=425–35 |pmid=8416051|s2cid=21226718 }}</ref>
These studies were followed by critiques of the methods used in early studies, which argued that biases in the methods used produced menstrual synchrony as an artifact.<ref name =Strassmann1997/><ref name=Wilson1992>{{cite journal |doi=10.1016/0306-4530(92)90016-Z |title=A critical review of menstrual synchrony research |year=1992 |last1=Wilson |first1=H |journal=Psychoneuroendocrinology |volume=17 |issue=6 |pages=565–91 |pmid=1287678|s2cid=16011920 }}</ref><ref name=Schank2000>{{cite journal |doi=10.1016/S0306-4530(00)00029-9 |title=Menstrual-cycle variability and measurement: Further cause for doubt |year=2000 |last1=Schank |first1=Jeffrey C |journal=Psychoneuroendocrinology |volume=25 |issue=8 |pages=837–47 |pmid=10996477|s2cid=29012907 }}</ref><ref name = Schank2001>{{cite journal |doi=10.1037/0735-7036.115.1.3 |title=Menstrual-cycle synchrony: Problems and new directions for research |year=2001 |last1=Schank |first1=Jeffrey C. |journal=Journal of Comparative Psychology |volume=115 |pages=3–15 |pmid=11334217 |issue=1|s2cid=45162956
More recent studies, which took into account some of these methodological criticisms, failed to find menstrual synchrony.<ref name = Strassmann1997/><ref name=Yang2006
===Terminology===
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===Evolutionary perspective===
Researchers are divided on whether menstrual synchrony would be adaptive.<ref name=Harris2013/><ref name=McClintock1998/><ref name =Strassmann1997/> McClintock has suggested that menstrual synchrony may not be adaptive but rather [[epiphenomenon|epiphenomen]]al, lacking any [[biological function]].<ref name=McClintock1998/> Among those who postulate an adaptive function, one argument is that menstrual synchrony is only a particular aspect of the much more general phenomenon of [[reproductive synchrony]], an occurrence familiar to ecologists studying animal populations in the wild. Whether seasonal, tidal, or lunar, reproductive synchrony is a relatively common mechanism through which co-cycling females can increase the number of males included in the local breeding system.
Conversely, it has been argued that if there are too many females cycling together, they would be competing for the highest quality males
Turning to the evolutionary past, a possible adaptive basis for the biological capacity would be reproductive levelling: among primates, synchronising to any natural clock makes it difficult for an alpha male to monopolise fertile sex with multiple females.<ref>{{cite journal|last1=Turke|first1=P. W.|year=1984|title=Effects of ovulatory concealment and synchrony on protohominid mating systems and parental roles|journal=Ethology and Sociobiology|volume=5|pages=33–44|doi=10.1016/0162-3095(84)90033-5}}</ref><ref>Turke, P. W. 1988. Concealed ovulation, menstrual synchrony and paternal investment. in E. Filsinger (ed.), ''Biosocial Perspectives on the Family.'' Newbury Park, CA: Sage, pp. 119-136.</ref><ref>{{cite journal|last1=Ostner|first1=J|last2=Nunn|first2=C. L.|last3=Schülke|first3=O.|year=2008|title=Female reproductive synchrony predicts skewed paternity across primates|journal=Behavioral Ecology|volume=19|issue=6|pages=1150–1158|doi=10.1093/beheco/arn093|pmc=2583106|pmid=19018288}}</ref><ref>{{cite journal|last1=Carnes|first1=L. M.|last2=Nunn|first2=C. L.|last3=Lewis|first3=R. J.|year=2011|title=Effects of the Distribution of Female Primates on the Number of Males|journal=PLOS ONE|volume=6|issue=5|page=e19853|doi=10.1371/journal.pone.0019853|pmid=21603570|pmc=3095636|bibcode=2011PLoSO...619853C|doi-access=free}}</ref><ref>{{cite journal|last1=Power|first1=C.|last2=Sommer|first2=V.|last3=Watts|first3=I.|year=2013|title=The Seasonality Thermostat: Female reproductive synchrony and male behaviour in monkeys, Neanderthals and modern humans|journal=PaleoAnthropology|volume=2013|pages=33–60|doi=10.4207/PA.2013.ART79|doi-access=free}}</ref> This would be consistent with the striking gender egalitarianism of extant non-storage hunter-gatherer societies.<ref>{{cite journal|last1=Dyble|first1=M.|last2=Salali|first2=G. D.|last3=Chaudhary|first3=N.|last4=Page|first4=A.|last5=Smith|first5=D.|last6=Thompson|first6=J.|last7=Vinicius|first7=L.|last8=Mace|first8=R.|last9=Migliano|first9=A. B.|year=2015|title=Sex equality can explain the unique social structure of hunter-gatherer bands|journal=Science|volume=348|issue=6236|pages=796–798|doi=10.1126/science.aaa5139|pmid=25977551|bibcode=2015Sci...348..796D|s2cid=5078886
===Media attention===
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The idea that menstruation is – or ideally ought to be – in harmony with wider cosmic rhythms is one of the most tenacious ideas central to the myths and rituals of traditional communities across the world.
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The [[!Kung]] (or Ju|'hoansi) hunter-gatherers of the [[Kalahari]] "believe ... that if a woman sees traces of menstrual blood on another woman's leg or even is told that another woman has started her period, she will begin menstruating as well".<ref>{{cite book |last=Shostak |first=M. |year=1983 |title=Nisa. The life and words of a !Kung woman |location=Harmondsworth |publisher=Penguin |page=68}}</ref> Among the [[Yurok|Yurok people]] of northwestern California, according to one ethnographic study, "all of a household's fertile women who were not pregnant menstruated at the same time...".<ref>{{cite journal |doi=10.1525/ae.1982.9.1.02a00030 |title=Menstruation and the power of Yurok women: Methods in cultural reconstruction |year=1982 |last1=Buckley |first1=Thomas |journal=American Ethnologist |volume=9 |issue=1 |pages=47–60|doi-access=free }}</ref>
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==Scientific details==
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In addition to the study they conducted with lesbian couples, Weller and Weller conducted a number of other studies on menstrual synchrony during the 1990s. In most studies they reported finding menstrual synchrony,<ref name=Weller1993a/><ref name=Weller1993/><ref name=Weller1997/><ref name=Weller1999/><ref name=Welleretal1999/> but in some studies they did not find synchrony.<ref name=weller1995/><ref name=Weller1995b/><ref name=Weller1998/> In a methodological review article in 1997,<ref name=WellerMethods1997>{{cite journal |doi=10.1016/S0306-4530(96)00037-6 |title=Menstrual variability and the measurement of menstrual synchrony |year=1997 |last1=Weller |first1=Leonard |last2=Weller |first2=Aron |journal=Psychoneuroendocrinology |volume=22 |issue=2 |pages=115–28 |pmid=9149333|s2cid=20297556 }}</ref> they refined their approach to measuring to better handle the problem of cycle variability. Specifically, they concluded that several menstrual cycles should be measured from each woman and that the longest average cycle length in a pair or group of women should be the basis for calculating the expected cycle onset difference.<ref name=WellerMethods1997/> Thus, their research falls into the pre-1997 methodology<ref name=Weller1992/><ref name=Weller1993a/><ref name=Weller1993/><ref name=weller1995/><ref name=Weller1995b/> and post-1997 methodology.<ref name=Weller1997/><ref name=Weller1999/><ref name=Welleretal1999/><ref name=Weller1998/>
[[File:PikiWiki Israel 16549 Womens Day.jpg|thumb|right|Bedouin women from Israel
In 1997, Weller and Weller published one of the first studies to investigate when menstrual synchrony occurs in complete families. Their study was conducted in [[Bedouin]] villages in northern [[Israel]]. Twenty seven families, which had from two to seven sisters 13 years or older and collected data on menstrual cycle onsets over a three-month period. Using the methods of,<ref name=WellerMethods1997/> they reported menstrual synchrony occurred for the first two months, but not for the third month for roommate sisters, close friend roommates, and for families as a whole.<ref name=Weller1997/>
[[File:Women pounding millet in Dogon country.jpg|thumb|right|upright|[[Dogon people|Dogon]] women pounding millet
Strassmann investigated whether menstrual synchrony occurred in a [[natural fertility]] population of Dogon village women. Her study consisted of 122 Dogon women with an average lifetime fertility rate of 8.6 ± .3 live births per woman. Their median cycle length was 30 days, which is indistinguishable from western women.<ref>{{cite journal |doi=10.1007/BF02692249 |pmid=24222401 |title=The function of menstrual taboos among the dogon |year=1992 |last1=Strassmann |first1=Beverly I. |journal=Human Nature |volume=3 |issue=2 |pages=89–131|s2cid=25712774 }}</ref> In analyzing whether menstrual synchrony occurs among Dogon women, she was aware of Wilson's<ref name=Wilson1992/> methodological criticisms of previous studies and aware that menstrual synchrony isn't synchrony ''per se'', but rather the closeness of menstruation among women. She used [[Proportional hazards models|Cox regression]] to determine whether the likelihood of menstruating was influenced by other women. She considered the levels of all the women in the village, all the women in the same lineage, and all the women in the same economic unit (i.e., they worked together). She found no significant relationship at any level, which means that there was no evidence of synchronization. She concluded that this result undermined the view that menstrual synchrony is adaptive and the view held by many anthropologists at the time that menstrual synchrony occurred in preindustrial societies.<ref name=Strassmann1997/>
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In order to work out why menstrual synchrony might have evolved, it is necessary to investigate why individuals who synchronized their cycles might have had increased survival and reproduction in the evolutionary past. The relevant field in this case is [[behavioral ecology]].
In mammalian mating systems generally, and among primates in particular, female spatio-temporal distribution – how clumped females are in the environment and how much they overlap their fertile periods – affects the ability of any single male to monopolize matings.<ref>{{cite journal |bibcode=1989RSPSB.236..339C |jstor=2410579 |title=Review Lecture: Mammalian Mating Systems |last1=Clutton-Brock |first1=T. H. |volume=236 |year=1989 |pages=339–72 |journal=Proceedings of the Royal Society of London. Series B |doi=10.1098/rspb.1989.0027 |issue=1285 |pmid=2567517|s2cid=84780662 |url=https://zenodo.org/record/8204699 }}</ref><ref>{{cite journal |doi=10.1126/science.327542 |title=Ecology, sexual selection, and the evolution of mating systems |year=1977 |last1=Emlen |first1=Stephen T. |last2=Oring |first2=Lewis W. |journal=Science |volume=197 |issue=4300 |pages=215–23 |pmid=327542 |bibcode=1977Sci...197..215E|s2cid=16786432
One implication is that there may be a link between the degree of synchrony in a population (whether seasonal, lunar or both), and the degree of reproductive egalitarianism among males. Foley and Fitzgerald<ref>{{cite journal |last1=Foley |first1=R. A. |first2=C. M. |last2=Fitzgerald |year=1996 |title=Is Reproductive Synchrony an Evolutionarily Stable Strategy for Hunter-Gatherers? |journal=Current Anthropology |volume=37 |issue=3 |pages=539–45 |jstor=2744554 |doi=10.1086/204516|s2cid=143968588 }}</ref> objected to the idea that synchrony could have been a factor in human evolution on the grounds that for hominins with inter-birth intervals of 3–5 years, achieving synchrony was unrealistic. Infant mortality would disrupt synchrony since it would be too costly for a mother who had miscarried or lost her baby to wait until everyone else had weaned their babies and resumed cycling before having sex and getting pregnant herself. On the other hand, while conceding that it would be impossible to get clockwork synchrony throughout an inter-birth interval, Power et al.<ref>{{cite journal |last1=Power |first1=C |first2=C |last2=Arthur |first3=L C |last3=Aiello |year=1997 |title=On Seasonal Reproductive Synchrony as an Evolutionarily Stable Strategy in Human Evolution |journal=Current Anthropology |volume=38 |issue=1 |pages=88–91 |jstor=2744440 |doi=10.1086/204586|s2cid=83484747 }}</ref> argued that once we take account of birth seasonality – enhancing the effects of menstrual synchrony by clumping fertile cycles within a relatively brief time-window – it emerges that reproductive synchrony can be effective as a female strategy to undermine primate-style sexual monopolization by dominant males. The controversy remains unresolved.
Adopting a compromise position, one school of Darwinian thought sets out from the fact that the mean length of the human menstrual cycle is 29.3 days,<ref>Jonathan R. Bull, Simon P. Rowland, Elina Berglund Scherwitzl, Raoul Scherwitzl, Kristina Gemzell Danielsson and Joyce Harper, 2019. 'Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles'. npj ''Digital Medicine'' 2:83; https://doi.org/10.1038/s41746-019-0152-7</ref> which is strikingly close to the 29.5 day [[Lunar day|periodicity of the moon]]. It is suggested that the human female may once have had adaptive reasons for evolving such a cycle length – implying some theoretical potential for synchrony to a lunar clock – but did so in an African setting under prehistoric conditions which today no longer exist.<ref>{{cite book |last=Knight |first=C. |year=1995 |title= Blood Relations: Menstruation and the Origins of Culture.|location=London & New Haven |publisher=Yale University Press, pp. 200-222.|url=https://books.google.com/books?id=UbaOAQAAQBAJ|isbn=9780300063080 }}</ref><ref>{{cite journal |doi=10.1017/S0959774300001190 |title=The Human Symbolic Revolution: A Darwinian Account |year=2008 |last1=Knight |first1=Chris |last2=Power |first2=Camilla |last3=Watts |first3=Ian |journal=Cambridge Archaeological Journal |volume=5 |page=75|s2cid=54701302 }}</ref> Not all archaeologists accept that lunar periodicity was ever relevant to human evolution. On the other hand, according to Curtis Marean (head of excavations at the important Middle Stone Age site of [[Pinnacle Point]], South Africa), anatomically modern humans around 165,000 years ago – when inland regions of the continent were dry, arid and uninhabitable – became restricted to small populations clustered around coastal refugia, reliant on marine resources including shellfish whose safe harvesting at spring low tides presupposed careful tracking of lunar phase.<ref name=Marean2010>{{cite journal |doi=10.1016/j.jhevol.2010.07.011 |title=Pinnacle Point Cave 13B (Western Cape Province, South Africa) in context: The Cape Floral kingdom, shellfish, and modern human origins |year=2010 |last1=Marean |first1=Curtis W. |journal=Journal of Human Evolution |volume=59 |issue=3–4 |pages=425–43 |pmid=20934095|bibcode=2010JHumE..59..425M }}</ref>
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===Olfactory Influences on menstrual synchrony===
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The main olfactory system, which receives sensory inputs from the olfactory mucosa and connects to the rest of the central nervous system via the main olfactory bulbs, and the accessory system, which receives inputs from the vomeronasal organ and connects to other brain centres via the accessory olfactory bulbs, are the two olfactory systems that are present in the majority of mammals (Scalia and Winans, 1976). There are connections from the olfactory bulbs to the hypothalamus, the brain region in charge of regulating the release of luteinizing hormone, in both systems.
In rats, the accessory system mediates the pheromonal action, [reviewed by Marchewska-Koj (Marchewska-Koj, in 1984)]. However, it appears that the pheromonal action in ewes and pigs is largely mediated via the primary olfactory system (Martin et al., 1986). (Dorries et al., 1997). If pheromones that mediate menstrual synchrony use the main olfactory system, a comparison of synchronised and non-synchronized women's ability to smell a particular pheromone can be used to infer a causal relationship between the ability to smell a pheromone and a potential role for the pheromone in mediating synchrony. In the current work, we looked at how menstrual synchrony and the sense of smell for the putative pheromones 3 androstenol and 5 androstenone related.<ref>{{Cite
===Non-human species===
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However, as with early human studies on menstrual synchrony, non-human estrous synchrony studies also were criticized for methodological problems.<ref name= SchankRatsPB>{{cite journal |doi=10.1016/S0031-9384(00)00395-4 |pmid=11239990 |title=Do Norway rats (Rattus norvegicus) synchronize their estrous cycles? |year=2001 |last1=Schank |first1=Jeffrey C |journal=Physiology & Behavior |volume=72 |issue=1–2 |pages=129–139|s2cid=15474640 }}</ref><ref name=SchankHamster>{{cite journal |doi=10.1006/hbeh.2000.1603 |title=Can Pseudo Entrainment Explain the Synchrony of Estrous Cycles among Golden Hamsters (Mesocricetus auratus)? |year=2000 |last1=Schank |first1=Jeffrey C. |journal=Hormones and Behavior |volume=38 |issue=2 |pages=94–101 |pmid=10964523|s2cid=23170432 }}</ref><ref name=SchankPrimates>{{cite journal |doi=10.1016/S0376-6357(01)00194-2 |title=Measurement and cycle variability: Reexamining the case for ovarian-cycle synchrony in primates |year=2001 |last1=Schank |first1=Jeffrey C |journal=Behavioural Processes |volume=56 |issue=3 |pages=131–146 |pmid=11738507|s2cid=46462822 }}</ref>
Subsequent studies failed to find estrous synchrony in rats,<ref name=SchankRatsAB>{{cite journal |doi=10.1006/anbe.2001.1757 |title=Oestrous and birth synchrony in Norway rats, Rattus norvegicus |year=2001 |last1=Schank |first1=Jeffrey C. |journal=Animal Behaviour |volume=62 |issue=3 |pages=409–75 |s2cid=54381210 }}</ref> hamsters,<ref name=Gattermann2002>{{cite journal |doi=10.1006/hbeh.2002.1800 |title=Asynchrony in the Estrous Cycles of Golden Hamsters (Mesocricetus auratus) |year=2002 |last1=Gattermann |first1=Rolf |last2=Ulbrich |first2=Karin |last3=Weinandy |first3=René |journal=Hormones and Behavior |volume=42 |pages=70–7 |pmid=12191649 |issue=1|s2cid=22337330 }}</ref> chimpanzees,<ref name=Mastsumoto2005>{{cite journal |doi=10.1002/ajp.20135 |title=Proximity and estrous synchrony in Mahale chimpanzees |year=2005 |last1=Matsumoto-Oda |first1=Akiko |last2=Kasuya |first2=Eiiti |journal=American Journal of Primatology |volume=66 |issue=2 |pages=159–66 |pmid=15940707|s2cid=23016072 }}</ref><ref name=Matsumoto2007>{{cite journal |doi=10.1007/s00265-006-0287-9 |title=Estrus cycle asynchrony in wild female chimpanzees, Pan troglodytes schweinfurthii |year=2007 |last1=Matsumoto-Oda |first1=Akiko |last2=Hamai |first2=Miya |last3=Hayaki |first3=Hitosige |last4=Hosaka |first4=Kazuhiko |last5=Hunt |first5=Kevin D. |last6=Kasuya |first6=Eiiti |last7=Kawanaka |first7=Kenji |last8=Mitani |first8=John C. |last9=Takasaki |first9=Hiroyuki |last10=Takahata |first10=Yukio |journal=Behavioral Ecology and Sociobiology |volume=61 |issue=5 |pages=661–8 |jstor=25511627 |bibcode=2007BEcoS..61..661M |s2cid=28097656 |display-authors=8 }}</ref> and
==== Rats ====
McClintock also conducted a 1978 study of estrous synchrony in Norway rats (''Rattus norvegicus''). She reported that the estrous cycles of female rats living in groups of five were more regular than those of rats housed singly. She also reported that social interaction, and more importantly a shared air supply that allowed for [[olfactory communication]] enhanced the regularity of the
The coupled-oscillator hypothesis asserted that females rats release two pheromone signals. One signal is released during the [[follicular phase]] of the estrous cycle and it shortens estrous cycles. The second signal is released during the [[Ovulation|ovulatory phase]] of the estrous cycle and it lengthens estrous cycles. When rats live together or share the same air supply, the pheromones released by each female in a group as a function of the phase of her estrous cycle causes other females in the group to either lengthen or shorten their estrous cycles. This mutual lengthening and shortening of estrous cycles was theorized to produce synchronization of estrous cycles over time.<ref name=McClintock1978/><ref name=McClintock1984>{{cite journal |doi=10.1016/0031-9384(84)90181-1 |pmid=6541794 |title=Estrous synchrony: Modulation of ovarian cycle length by female pheromones |year=1984 |last1=McClintock |first1=Martha K. |journal=Physiology & Behavior |volume=32 |issue=5 |pages=701–5|s2cid=35948410 }}</ref><ref name=SchankMcClintock1992/>
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====Lions====
Oestrus synchrony has been reported of [[lion]]s in the wild.<ref>{{Cite web|last=Hugo|first=Kristin|date=2016-08-23
==See also==
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* [https://www.nytimes.com/2008/02/05/health/05real.html "The Claim: Menstrual Cycles Can Synchronize Over Time"] – ''The New York Times'', February 5, 2008
* Dr. Harriet Hall, [http://www.sciencebasedmedicine.org/index.php/menstrual-synchrony-do-girls-who-go-together-flow-together/ Menstrual Synchrony: Do Girls Who Go Together Flow Together?] ''Science-Based Medicine'', September 6, 2011
{{Menstrual cycle}}
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