The flipper of a dolphin, the wing of a bat, the long legs of a horse, the digging hand of the mole, and the structure of a human hand all are used for entirely different purposes—yet they have exactly the same bones and muscles in them. In every case, there is an upper arm bone, a pair of lower arm
Animals build their bodies out of the structures they inherited from their ancestors, then transform these fundamental building blocks into completely different structures for swimming, flying, running, digging, grasping, or whatever they need to do. This shows that nature doesn’t engineer perfect solutions to biological problems, but “jury-rigs” the building blocks of the body that are already there. Nature isn’t a designer, but a tinkerer.