August 18, 2016 — Since the work of Charles Darwin, it has been more or less accepted that people, horses, porpoises, and bats share a common ancestor — one that’s arms and digits developed over many, many years to suit its needs. But only recent research has revealed that the human hand is actually extremely similar to the fin of a fish.
Although you wouldn’t know it comparing your hand side-by-side with a trout (and might only guess it watching Michael Phelps swim), human fingers and fish fins “follow some of the same rules,” The New York Times reports. In hands, we have a kind of tissue called “endochondral bone”; fish, however, have only small endochondral bones at the tip of their fin, the rest of the fin being made of rays of dermal bone. But by toggling with two genes related to limbs, scientists realized that the same cells in fish and in tetrapods either ask the body to develop dermal bones or endochondral bones.