Dec 7, 2010
The first air-breathing fish and amphibians extracted oxygen using gills when in the water and primitive lungs when on land. To do so, they had to be able to close the glottis, or entryway to the lungs, when underwater. The entryway, or glottis, to the lungs could be closed. When underwater, the animals pushed water past their gills while simultaneously pushing the glottis down. We descendants of these animals were left with vestiges of their history, including the hiccup. In hiccuping, we use ancient muscles to quickly close the glottis while sucking in air. Hiccups no longer serve a function. One of the reasons it is so difficult to stop hiccuping is that the entire process is controlled by a part of our brain that evolved long before consciousness.