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How Humans Ended Up with Such Awkward Plumbing
Humans are one of the few animals that routinely need to clean themselves after defecating. Why did evolution leave us with anatomy that seems less convenient than that of many other mammals? The answer lies in the changes that accompanied walking upright, along with the diets, habits, and environments of our ancestors.
J.J. Hinadaka
6/4/20263 min read
This question occurred to me while I was in the bathroom.
Most mammals seem to have a much easier time staying clean after defecating than humans do. Dogs, horses, and many other animals have an exposed anus and generally don't need to wipe. Humans, on the other hand, have an anus located between two large buttocks, which can make hygiene more complicated.
Considering that humans have had this anatomy for hundreds of thousands of years, long before toilets, running water, or toilet paper existed, it raises an interesting question: how did our ancestors manage?
At first glance, it almost seems like a design problem. If poor sanitation can spread disease, why didn't this become a major obstacle for human survival?
The answer is that the situation was probably not as problematic as it appears from a modern perspective.
How Walking Upright Changed Human Anatomy
One of the biggest differences between humans and our closest primate relatives is that humans walk upright full-time.
As our ancestors adapted to bipedal walking, the pelvis changed shape to support the body's weight and maintain balance. The muscles around the hips and buttocks also became much larger than those of other apes, especially the gluteus maximus, which plays an important role in stabilizing the body during walking and running.
The result is the familiar human buttocks. While this arrangement is useful for movement, it also means that the anus is positioned deeper between the surrounding tissues than it is in many other mammals.
The pelvic shift and muscle rearrangement from ape to human. Sumber: ResearchGate
Squatting May Have Helped
Early humans did not use modern toilets. They most likely squatted when defecating, a posture still common in many parts of the world today.
A deep squat changes the position of the hips and pelvis and can separate the buttocks more than sitting on a chair-height toilet. Some researchers have suggested that this posture may make bowel movements easier and more complete.
Although squatting would not eliminate the need for cleaning entirely, it may have reduced the amount of contact between feces and surrounding skin compared with some modern bathroom habits.
Early Human Diet Was... Probably Important
The diets of hunter-gatherers were very different from those of many people today.
They generally consumed more fibrous plant foods and fewer processed foods. Higher fiber intake is associated with larger, firmer stools that often pass more easily through the digestive tract.
Of course, prehistoric people were not immune to digestive problems. They experienced diarrhea, parasites, and intestinal infections just like any other human population. However, their typical diet may have reduced some of the hygiene challenges associated with many modern low-fiber diets.
When people think about diseases linked to human waste, they often think of events such as cholera outbreaks or other historical epidemics.
Here is why... Population Density Matters More Than Anatomy
These disasters were usually not caused by human anatomy itself. They were largely the result of large numbers of people living close together while sharing contaminated water sources and poor sanitation systems.
Early hunter-gatherer groups were small and mobile. Waste was dispersed across large areas rather than accumulating near dense populations. This reduced opportunities for many waste-related diseases to spread.
Knowing this, human anatomy starts to make more sense. Compared with many other mammals, our arrangement may seem awkward from a hygiene perspective. However, the human body did not evolve to maximize convenience or cleanliness. It evolved to help our ancestors survive and reproduce in the environments they lived in.
The same anatomical changes that helped humans walk long distances, run efficiently, and carry objects also produced the shape of the modern human buttocks. Any inconvenience associated with bathroom hygiene appears to have been a manageable trade-off rather than a serious evolutionary problem.
In other words, early humans did not survive despite their anatomy. They survived with it because their lifestyle, diet, and environment were very different from our own.
Note: This article was inspired by a bathroom thought and informed by reading about human evolution, anatomy, and hunter-gatherer lifestyles.