Why do grandmothers have sex? This is a question that baffles both young adults and evolutionary psychologists alike.
For the young adults, on the one hand, the mere thought of senior citizen sex is revolting. After all, with their supple bodies and unbounded energy, what could be more sexually unappealing than wrinkled faces and sagging flesh? Little can they comprehend that in four decades they’ll be in their sixties, still in the mood for love despite the infirmities of old age.
For evolutionary psychologists, on the other hand, the puzzle is why people who can’t reproduce still want to have sex. In fact, an evolutionary explanation for why sex drive wanes with age is known as the grandmother hypothesis. According to this theory, post-menopausal women experience a significant drop in sexual desire because they’re no longer able to reproduce . So instead they devote their reproductive energies toward raising their grandchildren.
It’s true that some women lose sexual desire after menopause. But it’s also true that other women experience a sexual flourishing around this time. Finally free of the fear of pregnancy and with a mature understanding of herself, a postmenopausal woman can now enjoy sex in ways she never could as a young woman—and she wants lots of it.
Another problem with the grandmother hypothesis is that it doesn’t deal with the grandfathers. Even men in their sixties are quite capable of fathering children, yet plenty of research shows that they too experience a decrease in sexual desire. As is always the case in psychology, the grandmother hypothesis is but one piece of the puzzle. Certainly it’s true that grandparents dote on their grandchildren, often lavishing more attention and resources on them than on their children. But grandma and grandpa can still take the grandkids to the park in the morning and have sex later in the day.
A further question is why humans get old in the first place. Among many species, adults maintain their vigor until a predator or a disease ends their life. In other species, old age is a swift ending to life. Take the salmon as an example. It spends its adult life in the ocean feeding until it’s strong and fat, and then it swims upstream to its spawning ground, where it mates one time, after which it quickly grows old and dies within a couple of weeks.
In humans, extended old age is partly due to advances in medical technology. But throughout history, plenty of people have thrived into their eighties and nineties. In fact, science hasn’t extended the maximum lifespan of humans. It’s only increased the likelihood that each of us will live a long life. Again, we get back to the same question: Why do humans continue to have sex when they can no longer reproduce?
If you’re as confused as the evolutionary psychologists, I’d like to suggest the reason is because you equate sex with reproduction. But before I explain, let me introduce a study by University of Nevada, Las Vegas psychologist Peter Gray and his colleagues, who surveyed the sexual behaviors of single adults ranging from 20 to over 70 years of age.
The survey sample consisted of 200-400 respondents in each of the following age ranges: 21-29, 30-39, 40-49, 50-59, 60-69, and over 70. Only single adults were targeted for this study so that individual sexual inclinations could be studied without the added complexities of marital dynamics. Three key questions asked were:
- Ideal sexual frequency. That is, how often they wanted to have sex.
- Actual sexual frequency. In other words, how often they did have sex.
- Sexual satisfaction. That is, how happy they were with their sex life.
Not surprisingly, the researchers found that both ideal and actual sexual frequency declined with age. Furthermore, sexual satisfaction increased with actual frequency of sex, especially when it approached the ideal frequency. However, when we compare gender and age, we find some interesting patterns.
The first finding is that men were less satisfied with their sex lives than were women, regardless of how old they were. This came as a surprise to the researchers, who expected men to become more satisfied with age. The reasoning was that since sexual desire decreases with age, the likelihood of an older man getting his sexual needs met should increase. However, regardless of age, ideal frequency of sex outpaced actual frequency, leading to sexual dissatisfaction.
The second finding was even more counter-intuitive. Older women reported being more sexually satisfied than younger women, even though their actual sexual frequency was lower. Because many women after menopause experience vaginal dryness or pain during intercourse, it was of course expected that older women would be less satisfied with their sex lives. But this was not the case.
The explanation for this unexpected result is complex. There was a significant minority of women over 60 who reported little or no sexual activity—and they were quite happy with that. In fact, these women provide support for the grandmother hypothesis. As hypothesized, they’ve apparently shifted their reproductive energies from bearing children to raising grandchildren.
Nevertheless, there are also post-menopausal women who reported enjoying frequent sex. Especially in Western society, too many young women find it difficult to enjoy sex. They aren’t given the information they need to make informed decisions, and they’re woefully unaware of their own sexual anatomy. They feel they shouldn’t enjoy sex because they’re afraid of being a “slut,” and often their young male partners don’t know how to properly pleasure them either. And, of course, as proper young women they can’t tell their male partners what their needs are, if they even know themselves.
Some Western women never learn to enjoy sex and are relieved when menopause ends the drudgery of having to sexually satisfy their spouses. Yet others take until middle age to overcome the inhibitions and negative messages of female sexuality in our culture. And once menopause releases them from the perils of pregnancy, they’re finally able to enjoy their sexuality to the fullest.
This last point brings us to the reason why the grandmother hypothesis is far from the full explanation for why sexual desire decreases with age. The point that evolutionary psychologists so often miss is that, in humans, sex has become decoupled from reproduction. Most species only have sex when the female is ovulating. But virtually all acts of human sex are conducted with the expectation that reproduction will not occur. In fact, we go to great lengths to prevent pregnancies. Modern science has given us condoms, the pill, intrauterine devices, and other methods of birth control.
Even in hunter-gatherer societies, people have lots of sex, but women rarely get pregnant. Women in these societies typically breastfeed their children for three or four years. Since lactation coupled with a low-fat diet and an active lifestyle shuts down ovulation, hunter-gatherer women can space out their pregnancies.
We humans don’t just have sex to procreate. Instead, we make love to build and maintain bonds with intimate others. That is to say, sex for humans is a social, not reproductive, act. Given this view of human sexuality, it’s no surprise that most of us keep doing it for as long as we’re able to. We may see a drop in desire as our stamina decreases. But grandma and grandpa still need intimate time with each other, just as younger couples do.