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{{cite journal|last=Yank|first=Zhengwei|coauthors=Jeffrey C. Schank|title=Women do not synchronize their menstrual cycles|journal=Human Nature|date=2006|year=2006|month=December|volume=17|issue=4|pages=433-447|doi=10.1007/s12110-006-1005-z|url=http://link.springer.com/article/10.1007/s12110-006-1005-z|accessdate=17 June 2013}}
{{cite journal|last=Yank|first=Zhengwei|coauthors=Jeffrey C. Schank|title=Women do not synchronize their menstrual cycles|journal=Human Nature|date=2006|year=2006|month=December|volume=17|issue=4|pages=433-447|doi=10.1007/s12110-006-1005-z|url=http://link.springer.com/article/10.1007/s12110-006-1005-z|accessdate=17 June 2013}}
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</ref><ref name = Ziomkiewicz2006>
{{cite journal|last=Ziomkiewicz|first=Anna|title=Menstrual synchrony: Fact or artifact?|journal=Human Nature|date=2006|year=2006|month=December|volume=17|issue=4|pages=419-432|doi=10.1007/s12110-006-1004-0|url=http://link.springer.com/article/10.1007/s12110-006-1004-0|accessdate=17 June 2013}}
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Menstrual or [[Estrous cycle|estrous]] synchrony has been reported in other species including [[Brown rat|Norway rat]]s<ref>
Menstrual or [[Estrous cycle|estrous]] synchrony has been reported in other species including [[Brown rat|Norway rat]]s<ref>

Revision as of 21:18, 17 June 2013

Menstrual synchrony is synchronization of menstrual cycles hypothesized to occur when women live together. Martha McClintock published the first study reporting the phenomenon of menstrual synchrony (also called the "McClintock Effect"[1][2]) among women living together under modern conditions. Most women report that they are aware of menstrual synchrony and nearly as many report personally experiencing the phenomenon.[3] And the question of whether women do in fact synchronize their menstrual cycles when they live together has received considerable attention in the popular media.[4][5][6][7]

After the initial studies reporting menstrual synchrony began to appear in the scientific literature, other researcher began reporting the failure to find menstrual synchrony in women.[8][9] These studies were followed by critiques of the methodologies used in early studies, which argued biases in the methods produced menstrual synchrony as an artifact.[10][11][12][13] More recent studies, which took into account some of these methodological criticisms, failed to find menstrual synchrony.[14][15][16]

Menstrual or estrous synchrony has been reported in other species including Norway rats[17], hamsters,[18] chimpanzees,[19] and Golden lion tamarins.[20][21]

Research

Humans

Martha McClintock, then an undergraduate, published the first study reporting on undergraduate women living in a dormitory in Wellesley College.[1] Her work was subsequently followed up by other studies reporting menstrual synchrony.[22][23] However, other studies were published that failed to find any trace of the phenomenon.[8][9]

For example, a study by Weller and Weller of 20 lesbian couples reported that more than half of the couples had synchronized within a two-day timespan of each other.[24], but Trevathana et al. conducted a study with 29 lesbian couples that showed no evidence of synchrony, and tentative evidence towards divergence of menstrual cycles.[9]

A subsequent study of traditionally living Bedouin women suggested that menstrual synchrony is not an automatic consequence of women residing temporarily in shared accommodation, conditions being optimal only when women develop close familiarity, co-operating with one another daily over extended periods of time.[25] One of the largest studies ever undertaken showed that women living in a Chinese dormitory for over a year did not synchronise.[15] Other papers have cast doubt on whether human females have the biological capacity to synchronise at all.[10][11] Adopting a compromise position, one school of Darwinian thought argues that the human female probably evolved with some capacity to synchronise, but did so under prehistoric conditions in the African savanna which today no longer exist.[26][27] Research on human menstrual synchrony is related to the question of whether there are human pheromones since McClintock hypothesized that human pheromones could synchronize cycles.[28][2][4]

Pheromones

Another study by McClintock and Stern (1998) investigated the possible existence of pheromone release/perception by human females as the possible mechanism for manipulation of the human menstrual cycle, the idea being that humans produced compounds that regulate neuroendocrine mechanisms in others, without the other party being aware of this event or consciously detecting any odor.[28] The study was conducted by collecting compounds from axillae (underarms) of donor women at prescribed phases during their menstrual cycles, and applying the compounds daily under the noses of recipient women. In order to collect the axillary compounds, the donor women wore cotton pads under their arms for at least 8 hours, and then the pads were cut into smaller squares, frozen to preserve the scent, and readied for distribution to the recipients. The recipients were split into two groups, and were exposed to the compounds via application of the thawed axillary pad under their noses daily.

The researchers concluded that odorless compounds collected from women during the late follicular phase of their menstrual cycles triggered hormonal events that shortened the menstrual cycles of the recipient women, and that odorless compounds collected from women during the time of ovulation triggered a hormonal event in the recipient women that lengthened their menstrual cycles. McClintock and Stern asserted that these findings "proved the existence of human pheromones" as well as illustrated manipulation of the human menstrual cycle.[28]

Human pheromones and chemosignals have also been studied in different contexts with regard to manipulation of the human menstrual cycle. Jacobs et al. examined the effects of natural compounds taken from breastfeeding women and their infants on the cycle length and cycle variance of recipient women. Axillary and breast secretions were taken from women who were exclusively breastfeeding and had not yet resumed menstruating. Recipient women met a set of selection criteria and were blind to the study aims and conditions. During the study, recipient women were exposed daily to the collected compounds, and the resulting effects on their menstrual cycles were tabulated. Exposure to compounds from breast feeding women and their infants increased variance in average cycle length among the women, and disrupted the cycles’ regulation. It also enhanced individual differences in cycle length and maintained the type of cycle length that a particular individual had at the time of exposure.[29]

Rats

McClintock also conducted a 1978 study of menstrual synchrony in rats (Rattus norvegicus). This study found that the menstrual cycles of female rats living in groups of five were more regular than those of rats housed singly. Social interaction, and more importantly a shared air supply that allowed for olfactory communication but prohibited auditory cues, enhanced the regularity of the rats’ cycles and coordinated their estrous phases after two or three cycles, resulting in synchronization. It is not known whether this synchrony and enhancement is the result of signals from a "leader" within the female group or if it is due to the interaction of several equal signals from each group member.[30]

This observation of menstrual synchrony in R. norvegicus is not the same as the Whitten Effect because it was the result of the continuous interactions of ongoing cycles within a female group, rather than the result of an exposure to a single external stimulus such as male odor, which in the Whitten Effect releases all exposed females simultaneously from an acyclic condition.[31]

Why might menstrual synchrony have been adaptive?

If we are trying to work out why menstrual synchrony might have evolved, we need to investigate why individuals who synchronised 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 monopolise matings.[32][33] The basic principle is that the more females are fertile at any one time, the harder it is for any single male to monopolise access to them, impregnating all simultaneously at the expense of rival males. In the case of nonhuman primates, once the number of co-cycling females rises above a critical threshold[34], a harem-holder may be unable to prevent other males from invading and mating with his females. A dominant male can maintain his monopoly only if his females stagger their fertile periods, so that he can impregnate them one at a time. Suppose a group of female baboons need between them just one dominant male, desirable in view of his high-quality genes. Then, logically, they should avoid synchronising their cycles. By the same token, if males during the course of human evolution became valued by females for additional purposes - hunting and bringing home food, for example - then females should resist being controlled by dominant male harem-holders. If males are useful partners to have and keep around, then ideally each female should have at least one for herself. Under those circumstances, according to this argument, the logical strategy would be for females to synchronise as tightly as they can.[35][36]

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[37] objected to the idea that synchrony was a factor in human evolution on the grounds that for hominins with interbirth intervals of 3-5 years, achieving synchrony was unrealistic. Infant mortality would disrupt synchrony since it would be too costly for a female who had lost an offspring to wait until the others started cycling again. On the other hand, while conceding that it would be impossible to get clockwork synchrony throughout an interbirth interval, Power et al.[38] argued that once birth seasonality is taken into account, synchrony can still be effective as a female strategy to resist primate-style sexual monopolisation by dominant males. The controversy remains unresolved.

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.[39]

Most studies of menstrual synchrony have been retrospective, introducing recall bias into the data.[40]

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.[40]

Methodological errors have also been proposed. A critical review of the evidence for menstrual synchrony gave this example:[40]

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.[40]

H. Clyde Wilson of the University of Missouri analyzed the research and data collection methods McClintock and others used in their studies. He found significant errors in the researchers' mathematical calculations and data collection as well as an error in how the researchers defined synchrony. Wilson's clinical research and his critical reviews of existing research, including the suggestion that pheromones can trigger synchrony in humans,[41] demonstrated that when the studies are corrected for such errors, the evidence for menstrual synchrony disappears.[42]

References

  1. ^ a b McClintock, Martha, K. (1971). "Menstrual synchrony and suppression" (PDF). Nature. 229 (229): 244–245. doi:10.1038/229244a0. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  2. ^ a b Anna Gosline (December 7, 2007). "Do Women Who Live Together Menstruate Together?". Scientific American. Retrieved 2 January 2012.
  3. ^ Arden, M. A. (1999). "Menstrual synchrony: Awareness and subjective experiences". Journal of Reproductive and Infant Psychology. 17 (3): 255–265. doi:10.1080/02646839908404593. Retrieved 17 June 2013. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: date and year (link)
  4. ^ a b Harriet Hall (Sep 06, 2011). "Menstrual Synchrony: Do Girls Who Go Together Flow Together?". Science-Based Medicine. Retrieved 2 January 2012. {{cite web}}: Check date values in: |date= (help)
  5. ^ MacLeod, Nadia. "Menstrual Synchrony". Retrieved 17 June 2013.
  6. ^ Adams, Cecil. "Does menstrual synchrony really exist?". The Straight Dope. Retrieved 17 June 2013.
  7. ^ O'connor, Anaha (2008). "The Claim: Menstrual Cycles Can Synchronize Over Time". New York Times. Retrieved 17 June 2013.
  8. ^ a b Wilson, H. Clyde; Kiefhaber, S; Gravel, V (1991). "http://www.sciencedirect.com/science/article/pii/0306453084900180". Psychoneuroendocrinology. 16 (14): 353–359. doi:10.1016/0306-4530(91)90021-K. Retrieved 16 June 2013. {{cite journal}}: External link in |title= (help)CS1 maint: date and year (link)
  9. ^ a b c Trevathan, Wenda R. Trevathan (1993). "No evidence for menstrual synchrony in lesbian couples". Psychoneuroendocrinology. 18 (5–6): 425–435. doi:10.1016/0306-4530(93)90017-F. PMID 8416051. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: date and year (link)
  10. ^ a b Wilson, H. Clyde (1992). "A critical review of menstrual synchrony research". Psychoneuroendocrinology. 17 (6): 565–591. doi:10.1016/0306-4530(92)90016-Z. PMID 1287678. Retrieved 16 June 2013.{{cite journal}}: CS1 maint: date and year (link)
  11. ^ a b Strassmann, Beverly (1999). "Menstrual synchrony pheromones: cause for doubt". Human Reproduction. 14 (3): 579–580. doi:10.1093/humrep/14.3.579. PMID 10221677. Retrieved 16 June 2013.{{cite journal}}: CS1 maint: date and year (link)
  12. ^ Schank, Jeffrey C. (2000). "Menstrual-cycle variability and measurement: further cause for doubt". Psychoneuroendocrinology. 25 (8): 837–847. doi:10.1016/S0306-4530(00)00029-9. Retrieved 17 June 2013. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  13. ^ Schank, Jeffrey C. (2001). "Menstrual-cycle synchrony: problems and new directions for research". Journal of Comparative Psychology. 115 (1): 3–15. doi:10.1037/0735-7036.115.1.3. Retrieved 17 June 2013.{{cite journal}}: CS1 maint: date and year (link)
  14. ^ Strassmann, Beverly I (1997). "The Biology of Menstruation in Homo Sapiens: Total Lifetime Menses, Fecundity, and Nonsynchrony in a Natural-Fertility Population". Current Anthropology. 38 (1): 123–129. Retrieved 17 June 2013. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  15. ^ a b Yank, Zhengwei (2006). "Women do not synchronize their menstrual cycles". Human Nature. 17 (4): 433–447. doi:10.1007/s12110-006-1005-z. Retrieved 17 June 2013. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  16. ^ Ziomkiewicz, Anna (2006). "Menstrual synchrony: Fact or artifact?". Human Nature. 17 (4): 419–432. doi:10.1007/s12110-006-1004-0. Retrieved 17 June 2013. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  17. ^ McClintock, Martha, K. (1978). "Estrous synchrony and its mediation by Airborne chemical communication (Rattus norvegicus)". Hormones and Behavior. 10 (3). doi:10.1016/0018-506X(78)90071-5. Retrieved 17 June 2013. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  18. ^ Handelmann, Gail (1980). "Social dominance determines estrous entrainment among female hamsters". Hormones and Behavior. 14 (2): 107–115. doi:10.1016/0018-506X(80)90002-1. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  19. ^ Wallis, Janette Wallis (1985). "Synchrony of estrous swelling in captive group-living chimpanzees (Pan troglodytes)". International Journal of Primatology. 6 (3). doi:10.1007/BF02745505. Retrieved 17 June 2013.{{cite journal}}: CS1 maint: date and year (link)
  20. ^ French, Jeffrey A. (1987). "Synchronization of ovarian cycles within and between social groups in golden lion tamarins (Leontopithecus rosalia)". American Journal of Primatology. 12 (4): 469–478. doi:10.1002/ajp.1350120403. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: date and year (link)
  21. ^ In non-human primates, the term may also refer to the degree of overlap of menstrual or estrous cycles, which is the overlap of estrous or menses of two or more females in a group due, for example, to seasonal breeding. Ostner, J. (2008). "Female reproductive synchrony predicts skewed paternity across primates" (PDF). Behavioral Ecoloty. 19 (6): 1150–1158. doi:10.1093/beheco/arn093. Retrieved 17 June 2013. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: date and year (link)
  22. ^ Graham, C.A. (1980). "Menstrual synchrony in female undergraduates living on a coeducational campus". Psychoneuroendocrinology. 5 (3): 245–252. doi:10.1016/0306-4530(80)90028-1. PMID 7191131. Retrieved 16 June 2013. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  23. ^ Jarett, Laura R. (1984). "Psychosocial and biological influences on menstruation: synchrony, cycle length, and regularity". Psychoneuroendocrinology. 9 (1): 21–28. doi:10.1016/0306-4530(84)90018-0. PMID 6739662. Retrieved 16 June 2013.{{cite journal}}: CS1 maint: date and year (link)
  24. ^ Weller A. Weller L. 1992. menstrual synchrony in female couples. Psychoneuroendocrinology. 17(2-3):171;177
  25. ^ Weller, A.and L. Weller 1997. Menstrual synchrony under optimal conditions: Bedouin families. Journal of Comparative Psychology, 111(2): 143-151.
  26. ^ Knight, C. 1995. Blood Relations: Menstruation and the origins of culture. London & New Haven: Yale University Press.
  27. ^ Knight, C., C. Power and I. Watts (1995). The human symbolic revolution: A Darwinian account. Cambridge Archaeological Journal, 5(1), 75-114.
  28. ^ a b c Stern, Kathy (1998). "Regulation of ovulation by human pheromones". Nature. 392 (6672): 177–179. doi:10.1038/32408. PMID 9515961. Retrieved 16 June 2013. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)CS1 maint: date and year (link)
  29. ^ Jacobs, S (2004). "Effects of breastfeeding chemosignals on the human menstrual cycle". Human Reproduction. 19 (2): 422–429. doi:10.1093/humrep/deh057. PMID 14747191. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  30. ^ McClintock, MK (1978). "Estrous Synchrony and its Mediation by Airborne Chemical Communication (Rattus norvegicus)". Hormones and Behavior. 10 (3): 264–276. doi:10.1016/0018-506X(78)90071-5.
  31. ^ McClintock, MK (1981). "The Social Control of the Ovarian Cycle and the Function of Estrous Synchrony". American Zoologist. 21: 243–256.
  32. ^ Clutton-Brock, Tim H. 1989. Mammalian mating systems. Proceedings of the Royal Society of London B 236: 339-372.
  33. ^ Emlen, S. T. and L. W. Oring 1977. Ecology, sexual selection and the evolution of mating systems. Science 197: 215-223.
  34. ^ Dunbar, Robin I. M. 1988. Primate Social Systems. London and Sydney:Croom Helm, pp. 140-43.
  35. ^ Knowlton, Nancy 1979. Reproductive synchrony, parental investment and the evolutionary dynamics of sexual selection. Animal Behaviour 27: 1022-1033.
  36. ^ Turke, Paul W. 1984. Effects of ovulatory concealment and synchrony on protohominid mating systems and parental roles. Ethology and Sociobiology 5: 33-44.
  37. ^ Foley, Robert A. and Charles M. Fitzgerald 1996. Is reproductive synchrony an evolutionarily stable strategy for hunter-gatherers? Current Anthropology 37: 539-545.
  38. ^ Power, Camilla, Catherine Arthur and Leslie C. Aiello 1997. On seasonal reproductive synchrony as an evolutionarily stable strategy in human evolution. Current Anthropology 38: 88-91.
  39. ^ Yang, Zhengwei (2006). "Women Do Not Synchronize Their Menstrual Cycles". Human Nature. 17 (4): 434–447. doi:10.1007/s12110-006-1005-z. Retrieved 2007-06-25. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  40. ^ a b c d Adams, Cecil (2002-12-20). "Does menstrual synchrony really exist?". The Straight Dope. The Chicago Reader. Retrieved 2007-01-10.
  41. ^ Wilson, H.C. (1987). Female axillary secretions influence women's menstrual cycles: A critique. Hormones and Behavior, 21, 536-546.
  42. ^ Wilson HC (1992). "A critical review of menstrual synchrony research". Psychoneuroendocrinology. 17 (6): 565–91. doi:10.1016/0306-4530(92)90016-Z. PMID 1287678.

External links

See also

Whitten effect


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