When and why did humans start wiping or manually cleaning themselves post-defecation, since animals generally don’t do this? —Roger

Many of humanity’s greatest pioneers—Newton, Edison, Rubik—have been fortunate enough to achieve household-name status for their groundbreaking work. Others, unluckier but no less visionary, must necessarily remain unknown. Sadly, we’ll never ID the first human to slide a digit or foreign object between the buttocks after doing number two, just as we’ll never locate the first person who decided it was a good idea to wash up afterwards. But we can figure out roughly when evolution would have made it necessary for our ancestors to develop a species-appropriate method of anal cleansing.

As you say, animals in general don’t make a habit of wiping after defecation—limbwise, few are up to the task anyway. Birds and fish would seem to lack means, motive, or both. Some mammals, it’s true, do clean themselves when necessary—think of your cat licking itself. (Maybe don’t think about it too long, though.) Only the most flexible hominids would be able to pull off that grooming trick, and the rest of us, I’d imagine, aren’t generally envious. Nor does it seem appealing to follow the lead of those species that occasionally drag their rumps along the ground to tidy up down below. (If you notice your dog engaging in such behavior, that’s more likely an attempt to relieve fluid buildup in the anal glands than some canine stab at hygiene.)

Our pressing need to wipe is the result of a significant anatomical difference separating us from the rest of creation. You and I may be so used to having them that we don’t think of our uniquely fatty, muscular posteriors as an evolutionary development that makes us stand out as humans—or, more precisely, stand up. Considered strictly as an adaptation, the glutes certainly don’t get all the good press that, say, the opposable thumb does. Nonetheless, the development of a stronger set of gluteal muscles was a major leap forward in enabling us to become an exclusively bipedal species.

It didn’t happen all at once—Australopithecus was strolling around upright nearly four million years ago with a body more akin to an ape’s than to ours. But eventually, between one and two million years ago, those of us who had sturdier hips and stronger muscles supporting them began to outrace our peers and our predators. The evolutionary advantage of the thickened layers of fat that cushion the glutes is less evident—some scientists speculate they offered a reserve that could be burned off for energy when food grew scarce.

Essential as they proved to be, butts came with issues. Our anal cavity was now tucked away within two mounds of flesh. From our present-day acculturated vantage point, this might seem like an obvious improvement, helping to keep the anus out of sight and mind. But for prehistoric folks it created a hazard that our animal friends, what with their exposed bungholes, rarely faced: fecal residue might linger in there, and the accumulation of bacteria in so moist a locale could cause infection. Women were especially vulnerable, given the proximity of the exposed vagina and urethra.

So one of these buttock-equipped humans—named by science Homo erectus, after their default posture—was probably the first wiper. Some rectal discomfort must have inspired this innovator to impulsively run a finger or two through the crevice and (ideally) wipe the accumulated crud off somewhere. H. erectus didn’t stand on formalities, after all. Perhaps over time those who engaged in the habit prospered, and taught their offspring to do likewise. Nobody said evolution was pretty.

As human culture progressed, of course, taboos and rituals developed around our eliminatory regimens, some apparently rooted in prudence, others in disgust. By the time of Deuteronomy, divinely ordained pooping instructions had been set forth, enjoining the Israelites to scoot out of camp before doing their business and bring a little shovel along to cover up the evidence. At length toilet paper enters the picture—though as I mentioned in a TP column way back in 1986, folks were ripping pages out of the Sears Roebuck catalog before softer tissue became more widely available. Even today, many cultures prefer the gentle cleansing of the bidet, as we discussed at some length last year when someone wondered if wiping was necessary at all.

Bear in mind that our ancestors might not have needed to wipe as vigorously or diligently as we do. Their diet, however omnivorous and haphazard, lacked the modern poisons that gunk up our GI tracts—Cheetos and Twinkies were hard to come by in paleolithic times, you know. And toilet use hadn’t yet trained them to relieve their bowels in an unnatural seated position. Squatting in the woods not only puts less strain on the system (possibly making squatters less prone to hemorrhoids) but allows smoother fecal passage, alleviating some of the need to wipe. Homo erectus had more to teach us, it seems, if we’d only been wise enough to listen. —Cecil Adams