Sorry, I can not indicate the source, but I read that menstrual cycles of women who live in the same house over time sync. Is it true? How does it work?
This is a myth which most likely came from methological flaws in the original study. It could never be reproduced. This paper ("Darwin’s Legacy: An Evolutionary View of Women’s Reproductive and Sexual Functioning") deals with it. The interesting part starts from page 30 and says (the references can be ressolved in the article):
Critiques of MSH Studies
Wilson (1992) and Yang and Schank (2006), among others, have criticized the study design, methods, and statistics used by McClintock (1971) and others who have claimed evidence of MS. For example, McClintock incorrectly used the Page test for ordered hypotheses with multiple treatments (she used the same groups of women repeatedly instead of independent treatments), making it impossible to evaluate the true level of significance of her reported findings. Likewise, reports of greater estrous synchrony in chimpanzees caged together than in those caged apart (Wallis, 1985) and synchronization of estrogen peaks in a sample of five golden lion tamarins (French & Stribley, 1987) are rendered moot by the use of unsuitable statistical tests (Schank, 2001). Furthermore, computer simulations suggested that the null hypothesis of no synchronization could not be rejected in either the chimpanzee or tamarin samples (Schank, 2001).