A sugar daddy’s sweet until he’s dead.

Hef and his now-wife, Crystal Harris, in 2011. | Ethan Miller/Getty Images

The half-dead millionaire with the platinum-blonde trophy wife on his arm is a tragically overused trope, but that doesn’t make the relationship any less fascinating. In high school, I enjoyed a brief flirtation with “The Girls Next Door,” E!’s campy reality show about octogenarian Hugh Hefner and his three girlfriends, one of whom was only 18. I accepted the polyamorous relationship at face value but got tripped up by the age difference?—?if nothing else, their sex life seemed medically ill advised.

Known colloquially as “May-December romances,” these mismatched couples captivate us in literature, movies and real life: Anna Nicole Smith’s 1994 marriage to 89-year-old businessman, J. Howard Marshall, convinced the public she married for money. Mick Jagger’s relationship with a ballerina less than half his age suggests he’s a tad reluctant to abandon his sex-symbol image. And the now 81-year-old Woody Allen’s marriage to his former step-daughter, 46-year-old Soon-Yi Previn, is too creepy to contemplate.

There is an evolutionary benefit to hot twenty-somethings and elderly men coupling off: The young women gain access to financial security and sexual diffidence (old dudes are p. safe) while their wizened mates revel in their partners’ youth and fertility. Both enjoy increased social clout, and sometimes, they might even be in love.

Of course, it’s all fun and games (and sex and money)?—?until somebody gets murdered. In 2012, a 27-year-old Polish trophy wife stabbed her 72-year-old husband after he accused her of cheating. In 2005, a British millionaire was convicted of murdering his trophy wife after she threatened to divorce him.

The sensational headlines make these relationships feel modern, but young women have been marrying men thrice their age for centuries. In an article for Bust, Mimi Matthews points to a book called “The Midwife’s Guide,” a 17th-century sex and midwifery manual. In it, the anonymous author takes issue with arranged marriages involving large age gaps, saying:

“When greedy parents, for the sake of riches, will match a daughter that is scarcely seventeen, to an old miser that is above threescore; can anyone imagine that such a conjunction can ever yield satisfaction, where the inclinations are as opposite as the months of June and January.”

You might assume the book’s chief concern was couples’ marital happiness, but you’d be wrong: The author had murder on the mind. He explains that incongruous marriages can only result in the wife cheating on or murdering her aged husband. He cites one specific example, in which a young woman conspired with her servants to strangle her wealthy husband in his bed before she ran off to London to live with a man her own age. Two years later, the woman and her staff were arrested and executed for the murder. The author laments that if only the bride had been matched to a man of similar age, everyone might still be alive.

The unknown author’s not only concerned with the murderous tendencies of young, desperate housewives?—?in a surprisingly feminist twist, he also worries about their sexual happiness. He writes that young women married to older men end up suppressing their “natural inclinations.” Even if they resist the impulse to stray, their youth and beauty guarantees their husbands will grow jealous and feel cuckolded. Interestingly, this idea pops up in classical literature: In Shakespeare’s “Othello,” Desdemona’s maid, Emilia, says, “But I do think it is their husbands’ faults if wives do fall.” In other words, it takes two to cheat?—?and a husband’s inadequacy may drive his wife into more forgiving arms.

According to the National Coalition Against Domestic Violence, more than ten million men and women in the United States suffer from physical abuse at the hands of an intimate partner every year. At least one-third of all women murdered in the United States are killed by their male partners. Clearly, marriages with large age gaps are not the only relationships that end in tears and bloodshed. However, the sensational aspects of these relationships guarantees headlines, reinforcing the idea that age might be a little more than just a number.