Last year, Tyler named “hypergamy” his word of the day.  He called the source “evil,” but the Evil One’s explanation is admirably elegant:

It is sometimes said that men are polygamous and women monogamous…It would be more accurate to say that the female sexual instinct is hypergamous.  Men may have a tendency to seek sexual variety, but women have simple tastes in the manner of Oscar Wilde: They are always satisfied with the best.

For a nice illustration, see the romance in Public Enemies.  Although Johnny Depp plays a murderer and a thief, he has his girlfriend’s true love.  Why?  Because he’s the nation’s Number One criminal.

Since I first learned the term, hypergamy’s explanatory power just seems to keep growing.  Let me share an example.  Last week, Robin reminded me that women initiate most divorces. This book says women initiate 91% of them; other sources say 65-75%.  Here’s how this pattern looks through the lens of hypergamy:

In marriage, a man and women contract to forsake all others.  Now ask yourself: If either were going to defect from this agreement, what form would the defection take?  Men, with a polygamous objective function, typically defect by trying to find an additional woman.   Women, with a hypergamous objective function, betray by trying to replace their existing man with a better one. 

It’s only natural, then, for the woman to initiate most divorces.  She has to lose her zero before she can renew her search for a hero.  The man, in contrast, gets little direct value out of initiating divorce; with polygamous preferences, divorce is inferior to remaining married while ignoring its constraints.  On further reflection, if fiction is any guide, a decent fraction of male-initiated divorces are probably the result of pressure from the “other woman,” who wants to have the two-timer all to herself.  So hypergamy explains even more than it seems: Why wives initiate divorce, and why mistresses pressure other women’s husbands to do the same.

In writing about betrayal, I don’t mean to sound overly cynical.  I’m not.  The world is full of men and women who not only take their marriage contracts seriously, but are too devoted even to want to break the agreement.   My point is simply that the betrayal takes very different forms – and the lens of hypergamy helps social scientists understand why.