Judson on Jews

Is It Really All in the Timing?

Yesterday, I went whacky, and entertained experiments beyond the cusp of knowledge. In today’s installment for Mad Scientist Week, I propose an experiment to look at an intriguing claim. Namely, that the sex practices of Orthodox Jews — which are strictly prescribed by Jewish law — dramatically increase the chances of having a son.

I came across this idea in a book called “Too Many Women?: The Sex Ratio Question,” by Marcia Guttentag and Paul F. Secord. In it, the authors present census data from towns in late 19th-century Russia. The population of the towns is broken into eight groups, including Muslims, Russian Orthodox, Armenians, and Jews. The sex ratio at birth for seven of the groups is about what you’d expect — around 106 boys for every 100 girls. This is typical of human populations where nothing weird is going on. (Parts of India and China now have very male-biased sex ratios, owing to the popularity of aborting female fetuses.) The Jewish data, however, is completely different. It varies from 127 boys for every 100 girls to 146 boys for every 100 girls.

There are two ways to interpret this data. The first is to assume that it’s wrong — that the births of little girls are going unreported. Indeed, according to the authors, some Russian demographers in the town of Odessa thought just that — they disbelieved the numbers they collected to such an extent that they falsified the census reports between 1892 and 1917 — “correcting” the sex ratio to 106 boys for every 100 girls.

The second is to assume that it’s right. In which case, what could account for it? There’s no reason I could discover to suspect infanticide. Another idea is that it could result from the pattern of abstinence and sexual activity that Jewish law demands. Which is a variation on a question that people have wondered about for more than 2400 years. Namely, does when you have sex affect whether you have a boy or a girl?

A wealth of studies have looked at this question. But they’ve reported conflicting results. Some have found you’re more likely to have a girl if you conceive around the day of ovulation; others, that you’re more likely to have a boy. Still others have found no effect. Why is there so much confusion?

To learn more, read the article.