Even Before Birth Control, More Sex Does Not Equal More Pregnancies
Also: What was the typical frequency of sex among married women in the 1920s?
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For fun, I’ve been looking at Marie Kopp’s data as reported in her 1934 book, Birth Control in Practice: Analysis of Ten Thousand Case Histories of the Birth Control Clinical Research Bureau. It’s a review of 10,000 cases between 1924-1429, more than thirty years before the first birth control pill was invented.
It’s an amazing book that I first ran into because it was referenced in Elisabeth Lloyd’s equally amazing Case of the Female Orgasm: Bias in the science of evolution. Here’s why I find the data amazing:
What Kopp’s data tells us is that there is no statistically significant relationship between frequency of intercourse and number of pregnancies.
Look:
Each line represents women with a particular number of pregnancies, from none to 10 or more. The flatness of the lines indicates that there is no relationship between frequency of intercourse (from “infrequent” to “daily”) and number of pregnancies.
This graph shows us the percentage of women reporting a particular number of pregnancies, and how often they report having intercourse. The lines are generally flat — not precisely flat, but not statistically different from flat — the correlation is literally 0. Zilch. Nada. I ran it through SPSS, my statistical analysis software, and SPSS said, “Dude, nuthin’.”
What this means is that there is no relationship between how often these women had sex and how often they got pregnant.
This result may sound slightly startling the first time you hear it, but as soon as you think about it for fifteen seconds, it makes perfect sense. After all, what does it take to get pregnant? There are at least two absolutely, utterly necessary components: the egg and the sperm.
Intercourse indicates that sperm is available.
But intercourse has no relationship at all to the egg.
The egg is available for very approximately one day a month. If the woman is in a fertile phase of life. And not already pregnant. And not breastfeeding with great frequency. And has a high enough body fat percentage to ovulate.
Also, about half of all fertilized eggs never implant, and a third of the ones that implant don’t make it past six weeks of gestation, which is so early that many women don’t even realize they’re pregnant. So even when an egg is available, the odds are still against pregnancy.
So of course there’s no relationship between how often a woman has intercourse and how often she gets pregnant. There’s only just barely a relationship between the times that she’s fertile and the times that she gets pregnant! Fertility is necessary, but not even close to sufficient.
The next time somebody suggests that human sexuality evolved for making babies, please remind them of how little relationship there is between how much sex we have and how many babies we make.
Humans reproduce sexually because we evolved from other mammals who reproduced sexually. But human sexuality, in all its kinky, complex, highly social, highly playful variety, evolved into its shape because sex is social first, and reproductive second.
But the data can tell us some amazing things about the realities of women’s sex lives in a world before hormonal birth control.
Have a look at this graph:
Each line represents women with a particular number of pregnancies. This graph shows us that women most have sex between 1-3 times per week, regardless of the number of pregnancies.
This time, each line represents not the percentage but the raw number of women, out of 10,000, reporting a given number number of pregnancies. In this graph it’s glaringly obvious what the most typical frequency of sex is: between 1-3 times a week — regardless of how many pregnancies the woman has had.
And then this:
Again, each line represents the number of women reporting a particular frequency of sex, and again, it’s glaringly obvious that the most typical number of pregnancies is between 1-4, regardless of frequency of sex.
So there you have it. 1-3 times per week, regardless of number of pregnancies. And out of the 10,000 women in the sample 50% had between 1-3 pregnancies.
Super sneaky extra bonus tidbit:
60 years later, Laumann et al’s Social Organization of Sexuality showed very much the same distribution of frequency of sex:
Kopp’s data compared with married and cohabiting individuals in Laumann et al’s 1994 data.
Apparently by 1994, couples were having slightly less sex — but mostly the same amount of sex — as couples were in 1934.
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