Why aren’t human fingers all the same length
The human hand is remarkably different from that of other primates， with shorter fingers， a smaller palm and a significantly stronger thumb. Of course， the most notable feature of our hands is the ability of the thumb to perfectly and comfortably oppose （come into square contact at the tips） each finger of the same hand.
The bases of the thumb， second and third fingers have all been strengthened to withstand greater stress， and in fact， the thumb has three muscles attached not seen in chimpanzees： the flexor pollicis longus， flexor pollicis brevis and first volar interosseous. Together， these make for a significantly stronger thumb that， along with some modifications to certain joints， allows for full， comfortable opposability.
Researchers have focused on several theories to explain why these changes occurred， and one of the most popular is that a better， stronger， finer grip was needed for making better tools and thus those who had such a grip had a distinct advantage in this way and others were selected out.
Another similar theory holds that our hands evolved thanks to the advantages this provides in accurately throwing and clubbing things. A third， equally violent theory acknowledges both of the first as potentially contributing factors， but notes that neither explains precisely why the hand holds its present， relatively stocky shape. Claiming however， to have the key to the “geometry” of our hands， adherents of this theory note that the human hand only becomes a truly strong weapon when it is formed into a fist.