To understand why women have affairs, we need to first understand the different types of mating strategies that humans adopt. Humans pursue two types of mating strategies- long-term and short-term, and sometimes a combination of both.
Long-term mating strategy typically 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.
In this post, we discuss the costs and benefits to women who have short-term affairs.
Human sperm competition
In humans, there’s immense intrasexual competition among males for females- both on a macroscopic and a microscopic level.
Everyone’s familiar with the macroscopic male intrasexual competition for a female- guys fighting over a girl.
But few know about the microscopic competition that takes place within the female reproductive tract among sperm cells of different males.
If a female copulates with more than one male during a short interval of time, the ejaculates from different males fight it out against each other to reach the egg- blocking, incapacitating, and even killing each other.
The important question is, what’s in it for the woman?
Healthy sperm = Healthy genes
If you look at a semen sample under a microscope you won’t see every sperm cell moving. While some of them move around frantically, others just stay there- lifelessly still.
The healthier the ejaculate, the greater is the percentage of motile sperm, and, the greater the percentage of motile sperm in an ejaculate, the higher are its odds of winning the sperm competition i.e. fertilizing the egg.
Therefore, when a woman promotes sperm competition by engaging in short-term mating, she’s basically seeking out the healthiest and the most competitive sperm to fertilize her egg with.
This strategy benefits the woman in the following ways:
First, she ensures that her offspring will have healthy genes. Second, if the offspring turns out to be a boy, he’ll produce a competitive ejaculate like his father. The son who’s likely to be successful in sperm competition, in turn, boosts the reproductive success of the mother.
All eggs in the same genetic basket
By pursuing the short-term mating strategy, a woman also avoids keeping all her eggs in the same genetic basket. By letting different men father her children, she ensures that her offspring are genetically diverse and have diverse immune systems.
This increases the odds of her children surviving the onslaught of infections and diseases. It wouldn’t have been the case had they been fathered by a single male.
If a woman’s regular mate isn’t attractive, she may be tempted to have affairs with attractive males. This way, her offspring can get access to better genes. She may even successfully trick her husband into raising kids that aren’t his own, like the female blue-footed booby bird.
Economics and sex
Unlike male sexuality, female sexuality has economic exchange value. What that basically means is that women can exchange sex for obtaining money, goods, or services.
It follows from the basic economic principle of supply and demand. Since men produce billions of sperm and women only a few hundred eggs, the latter are more valuable than the former. Consequently, female sexuality has more market value than male sexuality.
Women, much more than men, engage in prostitution- the world’s oldest profession. Some women may even sleep around to gain other advantages such as a promotion at work or better education for their children.
There’s a reason why men are rarely accused of, say, using sex ‘to move up the corporate ladder’ while women frequently face such kinds of accusations. Buyers of female sexuality far exceed the buyers of male sexuality.
Disadvantages of having affairs
Since men prize fidelity in potential wives, women risk impairing their desirability as long-term mates if they develop reputations for promiscuousness.
An unfaithful married woman risks the withdrawal of resources by her husband. Lacking a long-term mate to offer physical protection and help raise the kids, a woman who adopts an exclusively short-term sexual strategy is at a greater risk of physical and sexual abuse, endangering her life and the life of her children.
In the pursuit of casual sex, an unmarried woman risks getting pregnant and bearing children without the benefit of an investing man.
Also, there’s always a greater risk of contracting a sexually transmitted disease when engaging in short-term mating with multiple partners.