Romans' team is working on more research that compares menstrual cycle with other social and health variables in terms of what most determines mood, under the hypothesis that it's heavily weighted toward the latter. "The menstrual cycle signal was very small in terms of explaining the negative moods we were studying," she explains.

"I think this can be seen as the modern day equivalent of the old wandering womb notion," she told me, "that women are hysterical because of their reproductive system. And when a woman's upset, it's still often one of the first thoughts people have -- maybe she's premenstrual -- rather than 'Is her physical health bad? Is she under a lot of stress? Is she lacking social support?'"

"I go beyond that in my own thinking, which is that the whole PMS notion serves to keep women non-irritable, sweet, and compliant the rest of the time. There is a range of paradoxes -- world-turned-upside-down events -- like festivals, Mardi Gras, where people are socially prescribed to behave out of role. In Europe in medieval times there'd be one day a year where the lord would serve his own servants and workers, and then the rest of the time it's the other way, servant obeying the master. And these kinds of rituals serve to embed the normal behavior. I think PMS is a bit like that. 'We'll let you be cranky and bad-tempered now, but just for one or two days. The rest of the time you've got to be like a true woman.' Of course that's pretty feminist and hard to get data for, but at times I think it explains quite a lot."

Gender biases color the discussion in both directions, if unconsciously, but at least this study can inform more research on how we can keep everyone in the best mood possible, firstly by not overlooking pathology out of cultural expectation.

"PMS has been called a culture-bound syndrome in North America, and there are huge cultural differences in terms of how readily that explanation is reached for." There aren't, to her knowledge, cultures where a notion of PMS isn't a consideration, but there are many where the basics of the cycle are being re-evaluated.

"There's an anthropologist called Beverly Strassman who studied African tribes and has made the point that monthly menstruation is a very modern phenomenon. Women used to have later menarche, more pregnancies, longer periods of breast-feeding -- so in all they'd probably have half the number of menstrual cycles. Compared to modern women who have around 400 cycles during an active reproductive life. So there are important basic questions that remain unanswered. Is it healthy to have monthly menses? We really don't know."