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The hand is an extraordinary appendix, but is not exclusive to human: we share it with all the primates, but also with bats, cats, frogs and even dolphins.
Charles Darwin pointed out this strange coincidence in his The Origin of Species. “What’s more unique,” he wrote, “that the hand of man, conformed to grab, the paw of the mole, made for digging, the leg of the horse, the fin of the porpoise, and the wing of the bat all are structured according to the same pattern? “. For Darwin, the answer was clear: we humans are cousins of the bats and all other animals with hands; all we have inherited from a common ancestor.
Our hands began to evolve at least 380 million years ago by the flippers: not the flat ones of goldfish, but the robust and muscular ones of extinct relatives of today’s dipnoi. These lobed fins had some stubby bones inside that corresponding to those of our arms. Over time, the descendants of those animals also developed smaller bones, which corresponds to our carpal bones and phalanges. Later, fingers were formed, which, separating, allowed the animals to grasp the underwater vegetation. The first hands were the strangest of any today’s hand. There were species with seven and also with eight fingers. But 340 million years ago, when vertebrates had settled on the mainland, the fingers were reduced to five, and for reasons still unknown to science, their number has not increased.
The Primates’ arboreal life caused the arise of specific differentiations of their upper limb that, from the locomotor organ which was unique in mammals, turned into a specific adaptation to the grasp (prehensile organ), resulting in substantial changes in the extremities.