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One of the Beatles’ most beloved songs is “When I’m Sixty-Four,” the second track on Side 2 of their groundbreaking 1967 album, Sgt. Pepper’s Lonely Hearts Club Band. It features a 24-year-old Paul McCartney singing to his lover, asking whether she will still love him in the distant future, when he is a hopelessly ancient and decrepit 64-year-old.

When I get older, losing my hair

Many years from now,

Will you still be sending me a valentine,

Birthday greetings, bottle of wine?

This humorous, slightly schmaltzy ditty nonetheless poses a profound question for every long-term couple: Will you, in fact, find me attractive when we’re old? I had this very question in mind recently, as I contemplated the 34th anniversary of my own wedding. My wife wondered the same thing.

Neither of us is quite 64 yet (getting close), but I’m confident the answer for us both will turn out to be yes—though not for the things that attracted us to each other when we married, at 27. What keeps people in love is not what makes them fall in love in the first place. Understanding this might just keep your partnership intact until you are 64—and beyond.

The notion that romantic attraction is purely a function of social and cultural forces is a common assumption