Environmental influences cause menstrual synchrony, not pheromones

Abstract

To assess the influence of environmental conditions on the pattern of menstrual variation among women, data on menstrual cycles were recorded longitudinally from 127 university women who lived in a group of houses surrounding a central courtyard. Adequate follow-up was available on 76 women, among whom menstrual synchrony occurred in a short period of time. During the first month of coresidence, the day of menstrual onset deviated from the mean by an average of 13.7 days. During the next month, however, this average deviation declined to 2.6days. Moreover, it was found that menstrual synchrony occurred in the overall sample regardless of the house of residence, although synchrony occurred to a greater extent in some houses than in others. It would thus appear that common environmental influences play an important role in the overall pattern of menstrual cyclicity.

Multiple influences on menstrual synchrony: Kibbutz roommates, their best friends, and their mothers

“…Instead, following the procedure of Mc-Clintock (1971) and Quadagno et al (1981), pairs of subjects were randomly reassigned and tested for synchrony. Since the purpose of the control group was to determine whether similar life events (Little et al, 1989) and not pheromones could be the cause of menstrual synchrony, randomization was done separately for each kibbutz. Table 1 shows the frequency of intracouple differences in menstrual onset dates for pairs of roommates, pairs of best friends when the best friend also lived in the kibbutz, and women and their mothers.…”

“…In a recent report (Little et al, 1989), data on menstrual cycles were obtained for university students who lived in a group of houses surrounding a central courtyard. The finding that living in the same house within the courtyard led to greater synchrony than living in different houses that shared the courtyard led the authors to conclude that common environmental conditions play an important role in menstrual synchrony.…”

“…This leads us to conclude, like McClintock (1971), that the observed synchrony is not a result of environmental influences, such as eating in a common dining room; rather, the findings support the pheromonal explanation of menstrual synchrony. Nevertheless, the general question of whether menstrual synchrony is caused by pheromones or environmental influences is not a closed issue, particularly in view of the observations of Little et al (1989).…”

“…Prospective studies are preferred since they do not rely on the subjects' recall. Nevertheless, they often suffer from a substantial attrition rate; for example, Little et al (1989) reported that 37 of 127 women dropped out. In addition, all studies that rely on volunteers suffer from self-selection; for example, in Jarett (19841, 144 of 344 college women agreed to participate in the study.…”

“…However, Wilson (1987) claims that the data of Preti et al (1986), when reanalyzed, do not provide such evidence. Further, a recent study suggests a n alternative contention that common environmental influences are the major causes of menstrual synchrony (Little et al, 1989).…”