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“A man, who will kiss a pretty girl’s mouth passionately, may perhaps be disgusted by the idea of using her toothbrush.”—Sigmund

This quote by Freud shows us that disgust is a funny thing—and its importance in our everyday lives is woefully underrated.

Our abhorrence of things like vomit, feces, rotting food, and decaying dead bodies evolved to protect us from contamination by disease-causing germs.

But beyond that, Val Curtis of the London School of Hygiene and Tropical Medicine (described in a 2012 New York Times article as a “disgustologist”) believes that disgust is the guiding force for much of our as well. She points out that it not only dictates our hygiene behaviors, but also determines whether we choose to kiss someone or to run screaming in the opposite direction when he approaches.

Women Have a Lower Bar for Experiencing Disgust

Disgust researchers (not to be confused with disgusting researchers) such as Josh Tybur believe that we experience three distinct types of disgust: disgust that helps us to avoid disease, disgust that revolves around mate choice, and moral disgust over things that violate cultural or religious standards that we hold dear.

There does not appear to be a large difference between men and women when it comes to moral disgust, but research confirms that women set a much lower bar for feeling sickened by stimuli related to potential pathogens and stuff related to sexual activity. Consequently, women are less likely to work at jobs such as waste-water treatment, pest control, and janitorial work—and they find insects, incest, open sores, feces, and dirty clothing to be more revolting than do men.

Why would such a difference exist?

For sound evolutionary reasons, it makes sense that women would be more easily disgusted. Pregnant women are notoriously prone to nausea (i.e., morning sickness) as a way of protecting the fetus from pathogens, and, historically speaking, mothers have always mattered more to children than fathers do. They are more likely to be involved in food preparation, and they would more easily transmit pathogens to their children because they have more contact, and more intimate contact, with them.

Men Really Are More Disgusting Than Women

And let's face it—men are objectively more disgusting than women.

Bachelor pads have 15 times as many germs as women’s apartments—featuring specific yuck factors such as fecal material on their coffee tables—and men also have more bacteria on their hands and in their offices, which have been documented to be akin to giant Petri dishes.

So, why the female squeamishness about sex?

Why not? Sex can be filthy, if you do it right.

Between the sweat, semen, saliva, and body odor, it is a wonder that women have anything to do with the vile brutes at all. Ovulating women are especially sensitive to olfactory cues, and bad decisions are immensely costly to women. Aside from the risk of unwanted , women are at greater risk for sexually transmitted infections than men, and the risk of reputation damage can be significant. Women, out of necessity, have evolved to be wary of impulsive sexual activity.

For men, on the other hand, too much prissiness about sex would cut down on mating opportunities, which would work against a man's reproductive fitness. Fortunately, sexual arousal dampens women’s disgust response, keeping men in the game.

And men are not just dirtier—they are more ill-mannered and foul as well.

Some men never seem to completely outgrow the junior high school mindset of aspiring to be the grossest guy in the room. Men spit a lot more than women, and if one can eat or drink a more putrid concoction than one’s peers or become a virtuoso of disgusting body function sounds, one can attain a status in the group that most men covet but may never enjoy.

So where do these male impulses come from? How could such behavioral predispositions ever have been adaptive?

As an evolutionary psychologist, I am always curious as to what the payoff is in terms of mating success. While it is unlikely that women directly find such behavior attractive, it may very well be that it impresses the hell out of other men. And then, maybe, the status bestowed on a man by his peers can ultimately translate into success with women.

When you think about it, disgusting behavior is often also risky behavior. By eating or drinking things that might be contaminated or by risking social ostracism through the flouting of the polite rules of society, you are putting yourself on the line—you are risking serious illness or excommunication from the group, both of which would have been deadly in the brutal prehistoric world of our ancestors. If you can take such risks and survive them, you are showing others that you have special qualities.

Evolutionary biologists explain that such “honest signaling” is a way of demonstrating superior genetic or personal qualities that will make you a highly sought after political ally or a desirable romantic partner.

Recently, a team of anthropologists at UCLA led by Dan Fessler, tested what they called the “Crazy Bastard Hypothesis” in a series of studies.

Their Crazy Bastard Hypothesis gives us a fun and more complete way of thinking about risky male behavior—it may not only be about genetic quality, but it may also advertise how one might behave as an adversary or an ally. If you see a “crazy bastard” behaving with apparent disregard for his own personal well-being, doing things that ordinary men would away from, you definitely end up wanting to have that person as a friend rather than as an enemy.

In short, it can be very liberating to think of yourself as the most disgusting person in the room—as long as you are a man.