This episode is also on Bilibili too.
After two episodes in a row on fairly heavy topics, let’s take a breather today and talk about something a little more down-and-dirty: why do only humans need to wipe their butts?
When it comes to life’s most aggravating situations, few things beat going to the bathroom without toilet paper (the second most aggravating is dropping your phone into the toilet). When Xiang Shaolong, the original time-traveling pioneer, went back to the Qin dynasty, the first thing that troubled him wasn’t being unable to return to the present, or never seeing his girlfriend again—it was that paper hadn’t been invented yet in the Qin dynasty, so he had to scrape his butt with a piece of wood. When I watched A Step into the Past back then, I kept wondering whether Xiang Shaolong’s butthole ever received proper care afterward.
But why does this particular problem seem to belong only to us humans? Animals don’t seem to need to wipe their butts at all.
Strictly speaking, though, it’s not that they never wipe. My dog, Pineapple, occasionally drags his butt across the floor; and when cats groom themselves, they wash their faces and sometimes give their butts a lick too. But they aren’t like humans, who pretty much have to wipe after nearly every trip to the bathroom.
After doing some serious research, I think there are at least three reasons humans have to wipe our butts: our anatomy, our lifestyle, and our psychological and emotional makeup.
First, human anatomy has given us some extraordinary equipment. You could say our species has Earth’s number-one bubble butt, with two extremely well-developed gluteus maximus muscles. People always say corgis have great butts, but that’s all thanks to careful trimming. The human butt is the one that’s naturally gorgeous.
And why did these two enormous gluteus maximus muscles evolve? So that our two-legged, upright species could stay balanced while running. You may have heard that our butts stick out because they support upright walking, but that explanation isn’t quite right. Try putting your hand on your butt while walking and feeling around: when you’re merely walking, the gluteus maximus is actually relaxed and soft. Most of the time it doesn’t do much at all. But the moment you start running, those two gluteus maximus muscles tighten rhythmically in time with your stride.
When four-legged animals run, they don’t have to worry much about balance. With four feet on the ground, it’s hard for them to fall no matter what. Humans, on the other hand, have only two points of contact with the ground, so we’re especially prone to falling when we run. The gluteus maximus is what precisely controls our balance while running. So without such well-developed gluteus maximus muscles, we could still stand around happily enough, but we’d probably have a hard time running happily.
One of the most important hunting strategies of our ancestors was simply to run prey to death. Humans are such good runners partly because our sweat glands are excellent at shedding the heat generated by running, and partly because of the outstanding work of the gluteus maximus. In that light, humanity’s ability to rule Earth today means these two lumps of meat on our butts deserve a first-class medal.
But that also came with a small price: those two massive gluteus maximus muscles, together with the structure of our pelvis, wrap our butthole up deep inside them. In most other animals, the butthole and the butt are basically on the same plane, so poop rarely gets a chance to touch the butt. The human butthole, however, sits at the very bottom of a concave surface, which makes it especially easy for poop to stick to our butts. And so, naturally, we’re stuck wiping after every bathroom trip.
That brings us to the second reason humans have to wipe: changes in modern lifestyle. More specifically, I’m talking about the shift from squatting to sitting when we use the bathroom. If you want to reduce the odds of poop sticking to your butt, the most direct solution is obviously to flatten that concave surface as much as possible. The way to do it is—squat. When you squat down, the angle formed between the butthole and the butt is more likely to be obtuse; when you sit, it’s more likely to be acute. So which position makes poop more likely to stick to the butt? You can probably guess. That’s why modern people, who sit to use the bathroom, probably need to wipe more than people in the past, who squatted. This may also be why flushable wet wipes made specifically for wiping your butt have become increasingly popular in recent years. So before Xiang Shaolong traveled through time, he might have needed to wipe carefully—but once he got back to the Qin dynasty, scraping once with a piece of wood may really have been enough.
In fact, some research has found that when you use the bathroom in a position close to squatting, the angle of the intestines is more favorable for bowel movements than when you’re sitting. So one recommendation is that people with constipation who need to sit on the toilet try using a small footstool to raise their legs. That brings the sitting position closer to a squat and can help a lot.
The third reason humans have to wipe, then, has to do with psychology. Humans may be the most dirt-phobic species on Earth; dirty things can easily make us feel nauseated. We’ve conquered almost every visible natural enemy, but one invisible enemy still seriously threatens human life today: all kinds of disease-causing microorganisms. In the evolutionary arms race against bacteria and viruses, our ancestors developed certain psychological traits to protect themselves from microbial infection. The most important was an intense feeling of disgust toward all sorts of things that might contain disease-causing microorganisms—pus-filled wounds on the human body, rotting meat, and, of course, poop. Poop is a high-risk source of contamination where all kinds of disease-causing microorganisms can thrive. Many animals have an instinct to keep their bodies and homes clean, but some psychologists speculate that humans care about it more than any other species. So wiping our butts could be considered a human instinct—a self-protection mechanism.
All right, that’s enough on why humans need to wipe their butts. For more on what the gluteus maximus does, check out Daniel Lieberman’s excellent book Exercised. And for more on why humans are so easily disgusted, check out psychologist Rachel Herz’s book That’s Disgusting.
I’m Zhichao Wei. On this channel, I’ll keep sharing my three great passions—psychology, books, and movies. If you enjoy my programs, please follow, like, save, and comment; it really matters to me. I’ve put the research reports and references mentioned in this episode in the description below the video. Thanks for your support, and I’ll see you next time.
Leave a Reply