I’m reading Cordelia Fine’s Testosterone Rex: Myths of Sex, Science, and Society –it’s my airplane reading for today, as I travel east — and am getting increasingly enlightened. It addresses these terrible myths about men and manliness and sex that afflict us all, and most importantly, knocking down a lot of scientific fables that seem to be readily disseminated and accepted. Here’s an example from chapter two. She quotes a psychologist who describes a common hypothetical scenario, it’s even one that I think I’ve used in the past, the idea that the reproductive capacity of men is vastly greater than that of women, because we produce lots of cheap sperm, while they are limited by all that pregnancy and child-rearing stuff. Beat your chests in pride at your immense potential virility, men! She quotes a psychologist who makes this kind of facile quantitative argument.
Consider that a man can produces as many as 100 offspring by indiscriminately mating with 100 women in a given year, whereas a man who is monogamous will tend to have only one child with his partner during that same time period. In evolutionary currencies, this represents a strong selective pressure—and a potent adaptive problem—for men’t mating strategies to favor at least some desire for sexual variety.
Then — and this is what I love about this book — she takes it seriously and introduces all the factors involved in conception and does a simple calculation, assuming a man seriously goes on a crusade to impregnate 100 random women.
So what’s the likely return on this exhausting investment? For healthy couples, the probability of a woman becoming pregnant from a single randomly timed act of intercourse is about 3 percent, ranging (depending on the time of the month) from a low of 0 to a high of nearly 9 percent. On average, then, a year of competitive courtship would result in only about three of the one hundred women becoming pregnant. (Although a man could increase his chances of conception by having sex with the same woman repeatedly, this would of course disrupt his very tight schedule.) This estimate, by the way, assumes that the man, in contradiction with the principle of “indiscriminately mating,” excludes women under twenty and over forty, who have a greater number of cycles in which no egg is released. It also doesn’t take into account that some women will be chronically infertile (Einon estimates about 8 percent), or that women who are mostly sexually abstinent have long menstrual cycles and ovulate less frequently, making it less likely that a single coital act will result in pregnancy. We’re also kindly overlooking sperm depletion, and discreetly turning a blind eye to the possibility that another man’s sperm might reach the egg first. In these unrealistically ideal condition, a man who sets himself the annual project of producing one hundred children from one hundred one-night stands has a chance of success of about 0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000363.
(Number of zeroes only approximate — I just estimated from the layout on the page, which is hard to do. If only she’d used exponential notation!)
Let’s make the math even simpler and more stark.
Indeed, a promiscuous man would need to have sex with more than 130 women just to have 90 percent odds of outdoing the one baby a monogamous man might expect to father in a year.
Suddenly, my preferred reproductive strategy, monogamy and paternal investment in offspring, seems to be the best evolutionary strategy. It’s much less exhausting, too, and has given me time to do other things in my life.
Anyway, this is a delightful book that has made me question ‘facts’ I’ve long taken for granted multiple times so far, and I haven’t yet finished it. It really pays to think about one’s assumptions now and then, and it’s making me aware of how badly a lot of gender essentialism has poisoned our culture with lies.
She also takes a lot of swift, sharp pokes at evolutionary psychology, if you find that entertaining. I certainly do!