The designs we see in nature are not the result of chance. They rise naturally, spontaneously, because they enhance access to flow…
The similarities among animals that are on the surface very different are no coincidence. In fact, animal locomotion is no different than other flows, animate and inanimate they all develop in space and in time such that they optimize the flow of material.
For a finite-size system to persist in time (to live), it must evolve in such a way that it provides easier access to the imposed currents that flow through it.