For hundreds of thousands of years, 80% of women reproduced versus 40% of men. About 8,000 years ago, the rise of cities changed this ratio to 17 women for every 1 man. A few top males mated with hundreds or thousands of women. For example, geneticists estimate 8% of Chinese are descended from Genghis Khan. And 50% of Western Europeans are descended from a single Bronze Age king.

Before Western imperialism imposed Judeo-Christian values on the world, 83% of indigenous societies were polygynous, 16% were monogamous, and 1% were polyandrous. Polygyny is one man marrying multiple women. Polyandry is one woman marrying multiple men. Although some men had many wives, most engaged in serial monogamy—one long-term relationship followed by another.

Why would so many risk their reputations, families, careers—even presidential legacies—for something that runs against human nature? Were monogamy an ancient, evolved trait characteristic of our species, as the standard narrative insists, these ubiquitous transgressions would be infrequent and such horrible enforcement unnecessary.

-Christopher Ryan

Monogamous societies had fewer single men, which reduced rape and murder. Also, men shifted from seeking more wives to providing for their families. This increased gender equality and economic productivity.

In modern times, our evolutionary heritage continues to influence our relationships:

  • Polygyny is legal in 30% of countries

  • In non-polygynous countries like the United States, 80% of people marry, but nearly 50% of marriages end in divorce

  • High-status men such as Jack Nicholson, Wilt Chamberlain, and Mick Jagger, have sex with thousands of women

  • 15–20% of husbands and wives admit to cheating

  • 2–3% of fathers are unknowingly raising another man’s child

When looking for a life partner, my advice to women is date all of them: the bad boys, the cool boys, the commitment-phobic boys, the crazy boys. But do not marry them. The things that make the bad boys sexy do not make them good husbands. When it comes time to settle down, find someone who wants an equal partner. Someone who thinks women should be smart, opinionated and ambitious. Someone who values fairness and expects or, even better, wants to do his share in the home. These men exist and, trust me, over time, nothing is sexier.

-Sheryl Sandberg

Take a young man who started having sex at perhaps age 16 and who has gone for 10 to 15 years having a series of exciting sexual liaisons with a variety of women, some of whom he hardly knew. Then convince him to settle down and promise to have sex with only one woman for the next 60 years. Then let that woman grow older, plumper, less attractive, and let her sexual desires wane significantly while his desires remain close to what they were. Last, surround him at work and in his other activities with attractive younger women, some of whom are willing to have sex with him now and then. That will be the norm in the foreseeable future. What do you predict?

-Roy Baumeister

Beating the odds

Before getting married, here are factors that decrease divorce:

  • Personal income over $50,000 (-30%)

  • Waiting until marriage to have a baby (-24%)

  • Marrying over the age of 25 (-24%)

  • Religious (-14%)

  • College education (-13%)

During marriage, two of the strongest predictors of divorce are:

  • Financial disagreements

  • Negativity

Common disagreements include chores, quality time, in-laws, and sex. But a study of 4,500 couples found that financial disagreements were the only predictor of divorce for husbands. Finances and sex were predictors for wives.

Successful marriages typically have a 5:1 ratio of positive to negative behaviors. Disrespect, personal attacks, defensiveness, and withdrawal are especially damaging.

It takes a long time to be really married. One marries many times at many levels within a marriage. If you have more marriages than you have divorces within the marriage, you’re lucky and you stick it out.

-Ruby Dee

Overall, marriage is a partnership. There are different ways to provide value, such as making money, managing a household, having sex, and caring for children. Husbands and wives both want a fair deal—desire for fairness is hardwired into our species. If one spouse doesn’t contribute much, the marriage is unlikely to succeed.

The best way to get a good spouse is to deserve a good spouse.

-Charlie Munger

Look for someone who will love you unconditionally and will subtly encourage you to be better than you thought you can be.

-Warren Buffett


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  • Over the past 200,000 years, 40% of men reproduced vs. 80% of women

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  • 4,000–8,000 years ago, 17 women reproduced for every 1 man

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  • 8% of men in central Asia are descended from Genghis Khan and his descendants

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  • 50% of Western Europeans are descended from a male who lived 4,800–5,500 years ago

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  • A survey of 849 indigenous societies prior to Western colonialism found the following marriage patterns: general polygyny (42%), mild polygyny (42%), monogamy (16%), and polyandry (0.5%)

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  • Although polygyny is socially sanctioned in most societies, serial monogamy is the dominant type of marriage

  • Non-paternity rates range from 1.7 to 3.3% across societies

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  • Monogamous marriage may have been favored by cultural evolution because of group-beneficial effects such as lowering rape and murder rates, and increasing child investment, gender equality, and economic productivity

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  • Polygyny is legal in 58 out of nearly 200 sovereign states

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  • In 1995, it was estimated that 82% of men and 88% of women would get married over their lifetime

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  • From 2006 to 2010, the probability of a marriage lasting 20 years was 52% for women and 56% for men

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  • Fidel Castro, Jack Nicholson, Mick Jagger, and Wilt Chamberlain have slept with thousands of women

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  • 15–20% of men and women admit to extramarital sex

Beating the odds

Wilcox WB et al. (2009). The state of our unions: Marriage in America, 2009. National Marriage Project.

  • Risk of divorce is decreased by: personal income over $50,000 (-30%), waiting until marriage to have a baby (-24%), marrying over the age of 25 (-24%), religious (-14%), and college education (-13%)

Dew J, Britt S, Huston S. (2012). Examining the relationship between financial issues and divorce. Family Relations. 61(4): 615–628.

  • A study of 4,574 married couples over 3.5 years found that financial disagreements were the only predictor of divorce for husbands

  • Finances and sex predicted divorce for wives

  • Most common disagreements were chores, finances, time together, sex, and in-laws

Gottman JM, Levenson RW. (1992). Marital processes predictive of later dissolution: behavior, physiology, and health. J Pers Soc Psychol. 63(2): 221–233.

  • A 4-year study of 73 couples found that successful marriages had a 5:1 ratio of positive to negative behaviors vs. 1:1 or less for unsuccessful marriages

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  • A 14-year study of 79 married couples found that criticism, defensiveness, contempt, and stonewalling had a 52% correlation with divorce and a predictive accuracy of 83.5%

  • Criticism is personal attacks

  • Contempt is disrespect, mocking, sarcasm, ridicule, mimicking, and eye-rolling

  • Defensiveness is making excuses and playing the victim

  • Stonewalling is withdrawing from the interaction and not confronting issues

Birditt KS et al. (2010). Marital conflict behaviors and implications for divorce over 16 years. J Marriage Fam. 72(5): 1188–1204.

  • A 16-year study of 373 couples found that husbands and wives who reported more destructive behaviors had a higher rate of divorce

  • Destructive behaviors included yelling, criticism, belligerence, and contempt

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  • Humans and other cooperative species evolved a sense of fairness and aversion to inequity

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  • An fMRI study of 110 twin pairs found that rejection rate of unfair proposals had a heritability of 24–35%

  • Brain response to unfairness had a heritability of 37–40%

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