Why do we hiccup?

Of all the reflexes that we have, perhaps none is quite so pointless as the hiccup. The sound we all embarrassingly make on occasion is from 'trying' to forcefully inhale despite having closed off the trachea with the epiglottis. (The epigottis is a remarkable piece of tissue that usually shuts off access to the trachea when we ingest food or drink, thus protecting the airways from contamination. In this case, however, there is no food or drink to be seen.)

Why on earth would we have such a futile and annoying reflex? The leading theory at the moment is that hiccups are an evolutionary relic. That is, they are what is left of a reflex that was once useful to our distant ancestors, but which is useless now.

Say you were an amphibian (more particularly, a tadpole), and had both gills and lungs. Quite handy, no? But there are a few small issues to deal with. Most crucially, gills work by circulating water across them and then extracting the water's oxygen, whereas lungs obvious extract oxygen from the air. You can't therefore use both at once, unless you want to end up with water in your lungs - otherwise known as drowning. So when using their gills, tadpoles close the entrance to their lungs off, and inspire sharply, pushing water across their gills.

Are you seeing the pattern yet? We seem to do almost the same thing as these amphibians, except that it isn't useful to us anymore. The theory is thus that hiccups are an evolutionary relic, an almost discarded set of movements that highlights just how far we've come.