It’s commonly believed that organisms are perfectly evolved to their niches (“sharks are perfectly-designed underwater killing machines…”). This pops up all the time in pseudoscience, diet plans, natural-living manifestos and even academic discourse. But evolution is a game of averages: if a modification, on average, works better than a previous version, it’ll be kept, even if it causes pain or occasional death.

For example: A common hypothesis is that female pelvises are a compromise to a tricky problem: narrow hips, like males have, can run fast, but wider hips allow females to birth big-headed babies without dying. Female hips are good at neither, but adequate at both. Women are slow runners and childbirth kills a portion of the mothers and the children. But on average humans survive both lions and childbirth. The fallacy says that childbirth the way our ancestors did should be painless and low-risk. Evolution says it doesn’t care about your pain and death as long as enough women survive to keep the population going.

Evolution is a bitch. Other examples: hernias, sickle-cell anemia, and the blind spot in your vision.

Evolution can only modify existing organisms; it never goes back to the drawing board and every modification is just enough to make it work on average.

Feet are another classic example: Humans went from quadrapedal to bipedal very quickly. Our spines cranked into an s-curve so our hip joints could turn 90 degrees. Our ankle moved down (the “ankle” on your dog or cat is halfway up their leg, and looks more like a knee) and the foot bones hastily moved around to support weight and increase stability. Our feet are now a kluge, which works but is prone to problems. Evolution doesn’t care if your feet hurt at the end of the day if you can still escape from tigers and find a mate; it certainly didn’t bother “perfecting” either sharks or your feet. Hence, wear shoes.