The human body in itself is a powerful piece of evidence in favor of evolution — many of our physical traits make little sense other than as leftovers from back when we were fishy or four-legged. Smithsonian Magazine examines some of the oddest and most troublesome quirks:
Hiccups: The first air-breathing fish and amphibians extracted oxygen using gills when in the water and primitive lungs when on land — and to do so, they had to be able to close the glottis, or entryway to the lungs, when underwater. We descendants of these animals were left with vestiges of their history, including the hiccup. In hiccupping, we use ancient muscles to quickly close the glottis while sucking in (albeit air, not water). One of the reasons it is so difficult to stop hiccupping is that the entire process is controlled by a part of our brain that evolved long before consciousness, and so try as you might, you cannot think hiccups away.
Backaches: The backs of vertebrates evolved as a kind of horizontal pole under which guts were slung. It was arched in the way a bridge might be arched, to support weight. Then, for reasons anthropologists debate long into the night, our hominid ancestors stood upright, which was the bodily equivalent of tipping a bridge on end. Standing on hind legs offered advantages—seeing long distances, for one, or freeing the hands to do other things—but it also turned our backs from an arched bridge to an S shape. The letter S, for all its beauty, is not meant to support weight and so our backs fail, consistently and painfully.
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