- McClintock effect
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 inprisons ,convents ,bordello s, ordormitories ) tend to become synchronized over time.It is thought to be analogous to the
Whitten effect , which is the synchronization of theestrous cycle and has been noted in small animals such as mice andguinea pig s. In contrast to the Whitten effect, which is driven by malepheromone 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" in 1971. [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]A
prospective study by McClintock in 1998 was claimed to support her earlier findings by showing that underarm (or axillary) materials (collected from female donors), when wiped under the noses of (other) women, influenced cycle length. [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] Odors taken on the day that donors ovulated (and the next two days) delayed ovulation and hence lengthened the total cycle of the recipients. Therefore, these phase-advancing and phase-delaying effects show how human axillary compounds can regulate biological rhythms. [Weller, A (1998). "Communication through body odour". "Nature" 392: 126-27 ]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. [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 ]
Most studies of menstrual synchrony have been retrospective, introducing
recall bias into the data.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 ]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.
Methodological errors have also been proposed. A critical review of the evidence for menstrual synchrony gave this example:
This type of error is more likely in smaller sample sizes, like those used in studies of menstrual synchrony. One researcher has claimed that when the studies are corrected for such errors, the evidence for menstrual synchrony disappears. [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 ]
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 themoon . 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
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 ] Systems such aslunaception 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
External links
* [http://www.mum.org/mensy71a.htm The story of menstrual synchrony and suppression]
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