Why men have affairs (Short-term mating)

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Mating strategies in humans are essentially of two types- short term and long term.

The long-term mating strategy involves finding a long-term partner with whom one mates, has offspring and then raises those offspring. Short-term mating strategy, or having affairs, involves mating with more than one partner for short periods of time.

The long-term mating strategy makes good evolutionary sense because it promotes survival and reproductive success of offspring. However, the fact that both men and women do pursue the short-term mating strategy means that, in some contexts, pursuing a short-term mating strategy confers benefits too.

In this post, we discuss the costs and benefits to men who have affairs i.e. pursue the short-term mating strategy.

Tales of the testes

Ever wondered why men produce huge quantities of sperm cells (about 525 billion!) throughout their lives?

One answer lies in the phenomenon known as the ‘human sperm competition’.

If we look at human male testes in the context of other primates, they’re relatively large. Large testes produce more sperm and typically evolve as a consequence of intense sperm competition. Sperm from two or more males occupy the reproductive tract of a female at the same time. She has copulated with two or more males within a short interval of time.

Sperm competition thus exerts selection pressure on males to produce large ejaculates containing numerous sperm. In the race to reach the valuable egg, the larger, sperm-laden ejaculate has an advantage in displacing the ejaculates of other men in the woman’s reproductive tract.

This is also the reason why men, at the time of orgasm, shoot semen with an average speed of 28 miles per hour!

Surely, the ejaculate is trying to get somewhere important and is in a hurry to beat other folks in the way. 

Add to this the fact that sperm cells of different males in the reproductive tract of a female engage in warfare and literally kill or incapacitate each other to prevent each other from reaching the egg.

why men have affairs
Unsurprisingly, gorillas are less promiscuous and chimpanzees are more promiscuous than humans.

Now, how do you think an organism with large testes who can produce billions of sperm would maximize his reproductive success i.e. pass on as many genes as possible to the next generation?

It’s a no-brainer- by engaging in repeated, short-term mating with multiple partners. The more sperm that he successfully converts to offspring via fertilization, the higher will be the offspring that he fathers and therefore, the higher will be his reproductive success. Law of probability.

Long story short, men prefer a short-term mating strategy when all else is constant. This enables them to pass on maximum genes to the succeeding generations.

Now, this doesn’t mean that all men pursue the short-term mating strategy. It means that there’s a biological urge for men to do so. Whether or not they act on their urges depends on numerous environmental, social, cultural and contextual factors. (See why men have a stronger sex drive than women).

Anything that moves

Interestingly, while pursuing the short-term mating strategy, men seem to significantly relax the standards of women with whom they’d like to mate. Traits that they value in a long-term mate- kindness, intelligence, honesty, and fidelity no longer matter when they’re looking for casual sex. Just the fact that she’s physically attractive does it for them.

At times men even admit that they reach such high levels of desperation where it doesn’t even matter if the woman is attractive enough and that they’d basically have sex with “anything that moves.”

How preferences change

While seeking affairs, men seek women who seem sexually accessible- who wouldn’t make them jump through hoops before consenting to sex. Time, energy, and resources devoted to women unlikely to consent to sex would interfere with the successful pursuit of short-term mating.

Hence women who show signs of being prudish, sexually inexperienced, conservative or low in sex drive are disfavored. Clothes signalling sexual openness or behaviour signalling promiscuity which would be undesirable in a long-term mate might be desired by men in short-term mates solely because they suggest sexual accessibility.

Costs to men engaging in short-term mating

Other than the greater risk of contracting a sexually transmitted disease and threatening or destabilizing their long-term relationship (if they have any), the risks for men engaging in short-term mating are virtually non-existent.

Our early male ancestors must have indiscriminately pursued the short-term mating strategy to maximize their reproductive success. Those who didn’t were likely wiped out from the population by natural selection.

Hence, the biological drive to pursue short-term mating is strong in modern-day men because their male ancestors successfully pursued this strategy. You and I probably wouldn’t have existed if our early male ancestors didn’t pursue the short-term mating strategy.