And even within those last few thousand years, sexual exclusivity has often not been an ideal, at least not for men.

If we look at three important cultures that dominated Europe before Christianity, we see monogamous marriage as an important cultural institution, but one that imposed sexual faithfulness only on women.

I’m talking about Greek, Roman, and Celtic societies. While we know less about the Celts than the Greeks and Romans, we know enough to observe pretty confidently that Celtic men did not consider themselves to be socially bound to be sexually faithful to their wives.

Greek and Roman men were by no means legally or culturally bound to be sexually faithful to the women they were married to. Nobody (including their wives) expected them to be sexually monogamous.

I’m not holding these civilizations up as ideals worth emulating, of course. Their sexual and marriage arrangements were designed to keep men in charge and women inferior.

The legal and “ideals" situation changed with the advent of Christianity in Europe. Marriage gradually became understood to be a sexually monogamous institution for both men and women.

But … this was always a standard observed in the breach. Even though men were technically no longer free to have sex outside marriage, they did so anyway, constantly, to no real social consequence. Right up through the mid-20th century, wealthy men in Europe (and to a lesser extent North America) often set mistresses up with households and incomes — usually with their wives' knowledge.

Wives and mistresses were still required to be sexually faithful to men, but men did not as a rule feel bound to meet the same standard.

Men have throughout history tended to value (and enforce) sexual exclusivity in women while not requiring it of themselves.

I realize this is not the main point of your essay, which I enjoyed enormously, but I wanted to kick in with a little perspective on the sexist history of sexual exclusivity.