Considering that I wouldn’t be here without menstruation, I know so little about it. Not surprising, I guess, with the taboos and mystery that cloud menstrual blood.
Human females are among a few mammals that display menstrual blood -others are chimpanzees, bats and some shrews. Most mammals reabsorb their endometrial linings at the end of the cycle.
Not only is menstrual blood rare in mammals but so is “hidden estrus,” or concealed ovulation. That’s the narrow window in which women are fertile. Most female mammals make it clear when they are fertile. Science writer Virginia Sole-Smith explains:
“The vast majority of mammals signal fertility through estrus, the period when females are ovulating and display their sexual receptivity via genital swelling, behavioural changes or pronounced alterations in body odour. The female human body, however, conceals this critical window. Instead our most visible sign of potential fertility is menstrual blood, which, ironically, appears after the fertile period has closed (Scientific American, May, 2019).”
It’s puzzling why humans would have evolved to hide the most fertile time of a woman’s menstrual cycle. You would think that it would be to our advantage to advertise when fertility is greatest. But no, men are left clueless as to when a woman is most fertile.
One theory of why concealed ovulation might be an evolutionary advantage is that men are kept guessing. In their befuddlement, they keep trying to hit the window. This encourages pair-bonding. The success of raising children is increased when there are two parents. What the man gets out of it is greater confidence that the kid is his since he’s been hanging around for so long.
The taboos around menstrual blood have existed from the dawn of history to recent times. In 1920 a paediatrician working in Vienna published a collection of anecdotal observations: When he asked a menstruating woman to handle flowers, they wilted within minutes. When he compared the bread dough made by several women, the loaf made by the one having her period rose 22 percent less. The paediatrician concluded that menstrual blood contained a kind of poison.
And no wonder monthly periods have been called “the curse.” Estimates indicate that up to 80 percent of women experience cramps, bloating, fatigue, anger or other symptoms just before the onset of menstruation. Whose grand plan is that?
One controversial theory of premenstrual symptoms (PMS) has been put forward by Michael Gillings, a professor of molecular evolution at Macquarie University in Australia. He got some things right.
First, to the applause of some feminists, he questioned whether premenstrual symptoms (PMS) should be even classified as a disorder. Premenstrual dysphoric disorder (PMDD) had been added to the Diagnostic and Statistical Manual of Mental Disorders in 2013.
“Up to 80 percent of women report these symptoms; that makes PMS normal, not a psychological disorder,” Gillings said. “So we have to ask, ‘Was there, at some point in history, an advantage to having these symptoms?’”
Then Professor Gillings, to the chagrin of some feminists, suggested there was an evolutionary selective advantage to PMS because it caused tension between pair-bonds and therefore might help women dissolve relationships with infertile men.
Gillings was subsequently characterized as insensitive to the suffering of women. “I was burned in effigy on five continents,” he said.