Motor neurons controlling proximal limb movement in humans are molecularly identical to those controlling fin movement in fish.

“So the motor neurons, the neurons that control movement, uh they control movement of the trunk, they control movement of the fine digits of the fingers that are the fingers, the digits as we call them in science, right? Nerds speak, the wrists, everything. So we say from proximal to distal like from center out there's this incredible thing that's been discovered over the last 20 years or so which is that the molecular identities of the neurons that control the movement of my trunk and your trunk forward and back and side to side are exactly the same as the neurons that control undulation in a fish.”