The evolutionary glitch that makes you hiccup
In short: We have tried everything from drinking water to getting a sudden fright to stop them. Yet, despite modern medicine, the true purpose of the hiccup remains largely a mystery. This involuntary reflex might actually be a biological leftover from our ancient, water-breathing ancestors.
The hiccup is a simple reflex arc, much like the knee-jerk reaction seen in a doctor's office. It begins when a trigger causes the diaphragm—the muscle at the base of your lungs—to contract downward. As the lungs attempt to expand, the reflex forces the epiglottis, the flap at the top of your throat, to snap shut. This sudden closure creates the characteristic "hic" sound. This cycle repeats rhythmically until something manages to interrupt the neural arc.
While we often view hiccups as a modern nuisance, their roots are deep in evolutionary history. Some researchers suggest the reflex is a remnant of our transition from water to land. In our fish and amphibian ancestors, the phrenic nerve was much shorter, connecting directly from the brain to the gills. As mammals evolved, this nerve became a long, inefficiently shaped cord winding down the chest to the diaphragm. This extra length provides more surface area to be triggered, making the reflex more common in modern mammals, including dogs, horses, and rabbits.
The mechanism may have once been vital for survival. For amphibians moving between land and water, the ability to close the epiglottis allowed them to send water into the mouth and toward the gills without accidentally filling the lungs. While we no longer breathe underwater, the reflex persists. Dr. Dan Howes of Queens University in Ontario notes that the habit of suckling in baby mammals might also play a role, as infants hiccup much more frequently than adults. As the Mental Floss series highlights, debunking these common misconceptions helps us understand the strange, imperfect nature of evolution.
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Sources
- Summary by Intellect · source: Misconceptions about Hiccups- mental_floss on YouTube (Ep. 45) | Mental Floss
- Also: Why do we hiccup—and is there a better way to get rid of them?
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