“We prefer it,” the men told me at a dinner party where husbands and wives sat at entirely different tables in entirely different rooms.

Sex segregation, I was told, was a “choice.” But like “choosing” not to work, or a Dogon woman in Mali’s “choosing” to go into a menstrual hut, it struck me as a state of affairs possibly giving clue to some deeper, meaningful reality while masquerading, like a reveler at the Save Venice ball the women attended every spring, as a simple preference.

And then there were the wife bonuses.

I was thunderstruck when I heard mention of a “bonus” over coffee. Later I overheard someone who didn’t work say she would buy a table at an event once her bonus was set. A woman with a business degree but no job mentioned waiting for her “year-end” to shop for clothing. Further probing revealed that the annual wife bonus was not an uncommon practice in this tribe.

A wife bonus, I was told, might be hammered out in a pre-nup or post-nup, and distributed on the basis of not only how well her husband’s fund had done but her own performance — how well she managed the home budget, whether the kids got into a “good” school — the same way their husbands were rewarded at investment banks. In turn these bonuses were a ticket to a modicum of financial independence and participation in a social sphere where you don’t just go to lunch, you buy a $10,000 table at the benefit luncheon a friend is hosting.

Women who didn’t get them joked about possible sexual performance metrics. Women who received them usually retreated, demurring when pressed to discuss it further, proof to an anthropologist that a topic is taboo, culturally loaded and dense with meaning.

But what exactly did the wife bonus mean? It made sense only in the context of the rigidly gendered social lives of the women I studied. The worldwide ethnographic data is clear: The more stratified and hierarchical the society, and the more sex segregated, the lower the status of women.

Financially successful men in Manhattan sit on major boards — of hospitals, universities and high-profile diseases, boards whose members must raise or give $150,000 and more. The wives I observed are usually on lesser boards, women’s committees and museums in the outer boroughs with annual expectations of $5,000 or $10,000. Husbands are trustees of prestigious private schools, where they accrue the cultural capital that comes with being able to vouch for others in the admissions game; their wives are “class moms,” the unremunerated social and communications hub for all the other mothers.