09 Sep

We get hiccups because we lack gills

As featured on Brainwave|Amar Chitra Katha

Tanvi’s trying to stop a hiccup

Have you ever wondered why we get hiccups and why they’re so hard to get rid of? Is there a way out?

The part of our brain that is signalling us to hiccup is the brainstem. This is the same brain segment that directs swimming amphibians such as frogs to push water through their gills. In his book Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body, Neil Shubin, an anatomist at the University of Chicago, says that maybe this isn’t coincidence.

Source: Anatomography, maintained by Life Science Databases (LSDB) View License

As a foetus swimming in our mother’s womb, each of us had slits in our necks that were very similar to gills! We lost them by the time we were born, because we no longer needed them.

Shubin thinks that the brainstem’s habit of sending signals to gills got passed on from our amphibian-like ancestors. We may have lost gills along the way, but it seems that the gill signals stuck on. What happens when we have no gills to receive the signals? Hiccups!

A few years ago, in 2003, Christian Straus–a French scientist–showed that even though we humans don’t have gills anymore, the circuits in our brains that control them still exist. When there is a lack of oxygen or a rise in carbon dioxide around the throat (this often happens when we laugh a lot, or eat spicy food), these circuits get triggered. In creatures with gills, this would activate the gills, but with us it just causes a spasm, also known as a hiccup.

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