One fascinating table reveals how quickly couples end up in bed together. When asked about their most recent sexual partner, few (about 5 percent) say sex began “the day we met.” But about a fifth to a quarter say it began “after we met, but before [we were] in a relationship.” On the other end of the spectrum, about 5 percent say it took “more than a year,” and about 10 percent say it wasn’t until “after we got married.”

A common theory about casual sex is that it happens only for the “alpha males,” who “monopolize” the few women willing to engage in it while the “beta males” are left out. But this suggests a gender imbalance that doesn’t exist: The 10 percent of men with the most partners in Regnerus’s survey reported 52 percent of the (opposite-sex) sexual partners, compared with 48 percent for the top tenth of women. It seems that a small share of both men and women participate heavily in the casual-sex scene, though it’s likely still true that more men than women would fail in that scene if they gave it a shot.