Question: Why don't we have gills

Nikolai Adamski answered on 18 Mar 2015:

Well, we used to have gills, or better, a very distant ancestor us had gills. All life on the planet is thought to have its origin in the oceans, so naturally they had to be able to breathe under water.
At some point during evolution, different organisms started to conquer the dry land (bacteria, Algae, plants and then animals). At the beginning of “land fall” most animals will probably have been hybrids, i.e. being able to breath under and above water. But the more time a species spent on dry land the less need there was for gills, so eventually they were lost during evolution.
All our later ancestors kept living on land without gills and that’s why we don’t have any as well.
Maybe in a distant future we could change that, but that is a whole other story 🙂