Sunday, 5 June 2011
How many nostrils have you got?
Four. Two you can see; two you can't. This discovery came from observing how fish breath. Fish get their oxygen from water. Most of them have two pairs of nostrils, a forward-facing set for letting water in and a pair of 'exhaust pipes' for letting it out again. The question is, if humans evolved from fishes, where did the other pair of nostrils go? The answer is that they migrated back inside the head to become internal nostrils called choannae - Greek for 'funnels'. These connect to the throat and are what allow us to breathe through our noses. To do this they somehow had to work their way back through the teeth. This sounds unlikely but scientists in China and Sweden have recently found a fish called - Kenichthys campbelli - A 395 million year old fossil - that shows this process at its halfway stage. The fish has two nostril like holes between its front teeth. Kenichthys campbelli is a direct ancestor of land animals, able to breathe both in air and water. One set of nostrils allowed it to lie in the shallows and eat while the other poked out of the water a bit like a crocodile's. Similar gaps between the teeth can also be seen at an early stage of a human embryo. When they fail to join up, the result is a cleft plate. So one ancient fish explains to ancient human mysteries. The most recent research on noses, incidentally, shows that we use each of our two external nostrils to detect different smells, breathing different amounts of air into each to create a type of nasal stereo.