McClintock effect
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2008-06-22T22:20:16Z
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The '''McClintock effect''', also known as '''menstrual synchrony''' or the '''dormitory effect''', is a theory that proposes that the [[menstrual cycles]] of women who live together (such as in [[prisons]], [[convents]], [[bordello]]s, or [[dormitories]]) tend to become synchronized over time.
It is thought to be analogous to the [[Whitten effect]], which is the synchronization of the [[estrous cycle]] and has been noted in small animals such as [[mouse|mice]] and [[guinea pig]]s. In contrast to the Whitten effect, which is driven by male [[pheromone]]s, the McClintock effect is postulated to have only female pheromonal involvement.
==Research support==
The phenomenon, sometimes referred to as the "social regulation of ovulation," was first formally studied by psychologist [[Martha McClintock]], who reported her findings in ''[[Nature (journal)|Nature]]'' in 1971.<ref>{{cite journal |author=McClintock MK |title=Menstrual synchrony and suppression |journal=Nature |volume=229 |issue=5282 |pages=244–5 |year=1971 |pmid=4994256 |doi=10.1038/229244a0}}</ref>
A [[prospective study]] by McClintock in 1998 was claimed to support her earlier findings by showing that underarm materials (collected from female donors), when wiped under the noses of (other) women, influenced cycle length.<ref>{{cite journal |author=Stern K, McClintock MK |title=Regulation of ovulation by human pheromones |journal=Nature |volume=392 |issue=6672 |pages=177–9 |year=1998 |pmid=9515961 |doi=10.1038/32408}}</ref>
==Criticism==
If all women had an average-length menstrual cycle (of 28 days duration), the maximum time between two women's onsets would be 14 days and the minimum time between onsets would be zero days (synchronization). On average, the difference would be seven days, and (in small groups) half the time would be less (if one assumes there is no McClintock effect). McClintock observed a five day difference in her 1971 study and some have suggested this could have been a random occurrence.<!-- This argument boils down to statistics-- specifically, statistical significance. The five day difference may very well be statistically significant-- it is a question of how the data is analyzed and the noise in the data... need to pull the McClintock article. --><ref>{{cite journal | last = Yang | first = Zhengwei | coauthors = Jeffrey C. Schank | title = Women Do Not Synchronize Their Menstrual Cycles | journal = Human Nature | volume = 17 | issue = 4 | pages = 434–447 | year = 2006 | url = http://transactionpub.metapress.com/openurl.asp?genre=article&issn=1045-6767&volume=17&issue=4&spage=434 | accessdate = 2007-06-25 | doi = 10.1007/s12110-006-1005-z }}</ref>
Most studies of menstrual synchrony have been retrospective, introducing [[recall bias]] into the data.<ref name="cecil">{{cite web | last = Adams | first = Cecil | authorlink = Cecil Adams | title = Does menstrual synchrony really exist? | work = The Straight Dope | publisher = The Chicago Reader | date = [[2002-12-20]] | url = http://www.straightdope.com/columns/021220.html | accessdate = 2007-01-10 }}</ref>
The interaction of theorized menstrual synchrony with differing cycle lengths has not been explained. Two women with cycle lengths that differed by two days might initially begin menstruating on the same day, but the next month would be two days apart, the month after that four days, and so on. No studies have claimed to show that the McClintock effect causes women with historical cycles of different lengths to synchronize.<ref name="cecil" />
Methodological errors have also been proposed. A critical review of the evidence for menstrual synchrony gave this example:<ref name="cecil" />
{{quote|Suppose a study starts on October 1. Subject A, with a 28-day cycle, has an onset on September 27, another on October 25, and a third on November 22. Subject B, with a 30-day cycle, has an onset on October 5 and another on November 4. A naive investigator could report that these subjects were 20 days apart at the outset (October 25 vs October 5) and 18 days apart at their second onset (November 4 vs November 22). Therefore, the two are synchronizing. In fact, the two subjects were eight days apart to start with (September 27 vs October 5) and are diverging.}}
This type of error is more likely in smaller sample sizes, like those used in studies of menstrual synchrony.<ref name="cecil"/> One researcher has claimed that when the studies are corrected for such errors, the evidence for menstrual synchrony disappears.<!--
--><ref>{{cite journal |author=Wilson HC |title=A critical review of menstrual synchrony research |journal=Psychoneuroendocrinology |volume=17 |issue=6 |pages=565–91 |year=1992 |pmid=1287678 |doi=10.1016/0306-4530(92)90016-Z }}</ref>
Some consider the McClintock effect to be a statistical artifact or [[fallacy of causation]], and the actual cause of the synchrony to be not pheromones, but the influence of the [[moon]].<!--
--><ref name="knight">{{cite book | author = Chris Knight | title = Blood relations: menstruation and the origins of culture | publisher = Yale University Press | location = New Haven, Conn | year = 1991 | id = ISBN 0-300-04911-0}}<br><!--
-->{{cite journal | last = Knight | first = Chris | coauthors = Camilla Power & Ian Watts | title = The Human Symbolic Revolution: A Darwinian Account | journal = Cambridge Archaeological Journal | volume = 5 | issue = 1 | pages = 75–114 | date = 1995 | url = http://www.radicalanthropologygroup.org/pub_knight_power_watts_big.pdf | accessdate = 2006-12-13 }}</ref> Systems such as [[lunaception]] and cosmo-fertility, which provide complex explanations of the moon's effect on reproductive cycles, are at present not regarded as having a scientific basis.
==References==
<references/>
==External links==
*[http://www.mum.org/mensy71a.htm The story of menstrual synchrony and suppression]
[[Category:Menstruation]]