Nobody wants to change a dirty diaper, but it sure seems like new dads are a bit more tolerant of those noxious fumes than new moms. And it’s not just society telling us that macho men have stronger stomachs than delicate women — studies have shown robust differences in how the sexes respond to disgust. Researchers have found that women tend to display higher levels of disgust than men when asked about insects, open sores, dirty clothing, feces, rotten food, and death.
Evolutionary biologists have proposed several explanations as to why natural selection may have given us moms who are more averse to dirty diapers than dads. Here are a few of their theories.
Sorry Dads. Mothers Matter More
Ask any population geneticist and he or she will tell you the disappointing truth. Dads may play a role in ensuring the health and survival of their offspring, but mothers tend to be more dedicated parents than fathers. Nature knows that, so it works hard to keep women alive. Studies suggest that this may be why women evolved to be more risk-averse than men. And some researchers suspect it’s also why women are wired to avoid disgusting dangers, from rotten food to human waste.
“If mothers matter more to the health and survival of offspring than do fathers, then from a genetic perspective the male vehicle is more expendable than the female vehicle,” psychologist Laith Al-Shawaf writes in his study on the differences between male and female disgust. “Selection will therefore act more intensely on female psychology to avoid harm.”
When Moms Get Sick, So Do Their Kids
Between gestation, breastfeeding, and simply spending more time holding their babies, studies have shown that women are significantly more likely to pass diseases on to their kids. Which means they need to be more careful than men in order for our species to survive. One manifestation of this carefulness could be heightened sensitivity to disgusting items that may harbor disease.
“Women who were more easily disgusted were probably less likely to contract an infection,” Al-Shawaf writes. “And consequently less likely to pass on this infection on to their offspring.”
Ancestral Women Taught Us to Wash Our Hands
Moms tend to take more active roles in educating their children — and a good part of educating children is teaching them not to put disgusting things in their mouths. Evolutionary biologists suspect that, over time, women developed an innate sense of disgust for disease-causing items specifically to optimize their ability to warn their children away from disease. One side effect is that, even if dads are the family hand washers, moms are wired to be most disgusted by dirt.
“Ancestral women would have benefited from elevated disgust in their prominent role in keeping children away from disease,” Al-Shawaf writes. “Ancestral women had to be disgusted for two.”
And Kept Our Food Safe From Pathogens
In most hunter-gatherer tribes, men hunt while women clean and prepare the food. Which means that tribes stocked with prudent women who chose to discard smelly cuts of meat and were fastidious about cooking out pathogens may have been more likely to survive. The evolutionary outcome, so goes the theory, is that the most easily disgusted women lived to reproduce, and raise a generation of modern women who are grossed out by dirty diapers.
“Elevated disgust and greater prudence with contaminated food would have paid fitness dividends in lower disease rates for women, their mates, their offspring, and other genetic relatives,” Al-Shawaf writes. “Because of men’s lesser impact on food hygiene and food preparation, this particular selective pressure would have been weaker on males.”
Ancestral Men Needed Strong Stomachs For War And Sex
Most evolutionary theories that explain why modern women are more easily disgusted than men assume that disgust is aberrant, and so it must have been evolutionarily acquired by women who needed to become disgusted in order to survive. But there’s one noteworthy theory that assumes just the opposite. Women have perfectly normal levels of disgust, and men once did too, the theory goes — until natural selection favored guys who powered through their disgust.
One example: Unlike women, who make long-term and high-risk investments in procreating, men don’t lose energy and resources (at least not meaningfully so) to the act of reproduction. Even their risk of contracting a sexually-transmitted disease is far lower than that of women. Which means ancestral men who were the least disgusted by diseased female partners benefitted. “Reduced levels of pathogen disgust may increase the number of potential mates one is willing to have sex with, as well as the number of contexts in which one is willing to have sex,” Al-Shawaf writes. The natural consequence? Men with low sensitivity to disgust may have passed their nonchalance to more kids.
And since hunting and warfare are traditionally male activities, a similar theory suggests that men may have acquired a high tolerance for disgust because those who didn’t appreciate animal carcasses, severed limbs, and open wounds were socially ostracized. “Low disgust thresholds in men would have interfered with their ability to hunt, combat enemies, help wounded allies, and transport bloody and injured bodies back to camp,” Al-Shawaf writes. “These selective pressures were partly responsible for raising male disgust thresholds.”