Why do women menstruate? Menstruation is a peculiar phenomenon that women go through on a roughly monthly cycle, and it’s not immediately obvious from an evolutionary standpoint why they do it.
It’s wasteful — they are throwing away a substantial amount of blood and tissue. It seems hazardous; ancestrally, in a world full of predators and disease, leaving a blood trail or filling a delicate orifice with dying tissue seems like a bad idea. And as many women can tell you, it’s uncomfortable, awkward, and sometimes debilitating. So why, evolution, why? One assumption some people might make is that that is just the way mammalian reproduction works. Phylogeny showing the distribution of menstruation in placental mammals and the inferred states of ancestral lineages.
Both alike in dignity. Three post (this one, this one, and, most recently, this one) on the differences between men’s and women’s sexuality calls for at least one post on how they’re ALIKE.
The way I describe the relationship between men’s and women’s sexuality is the same way I describe the relationship between men’s and women’s genitals: “Same stuff, just organized differently.” With regard to genitals, I’m talking about biological homology, something I’ve talk about a couple of times (though it turns out I’ve never written an entire post about it – another one for the growing list of things to do). With regard to function I’m mostly talking about the central nervous system – specifically the dual control model, the only theory of sexual response I know of that describes the actual MECHANISM underlying desire and arousal, rather than merely describing behavior or experience.
The short version: Men’s and women’s sexualities are both made up of these two components. Like this: Like Loading... Why do those who advocate home birth feel the way they do? Menstruation: lunar? pheromones? synchronised? You'd have thought, given that periods have been a universal experience for women for millennia, that we'd know all there is to know about them by now.
In truth, we still seem to be debating the basics: how a woman's cycles differ from one month to the next, and between one woman and another, whether women who live together cycle together - even whether it's the moon that makes us menstruate. The average British woman has 400 periods in her lifetime, whereas a woman from the Dogon tribe in Mali, who will probably have about eight children, will have only 110 periods - just as well, because the Dogon get banished to a special "menstrual hut" each time. So, while the total number of periods seems to be well established, the mythology begins with "average" cycle length. Normal is 28 days. Oh, no it isn't. It was an American, RF Vollman, who showed that 28-day cycles are the exception rather than the rule.