Human Body
Why do humans and similar animals have 5 fingers (or four fingers and a thumb) and not some other number? (I'm presuming the number of non-thumb fingers is even because it's 'easier' to create them in pairs.)
Is it a matter of the relative advantage of dexterous hands and the opportunity cost of developing more? Seven or nine fingers would seem to be more useful than 5 if a creature were being designed from the ground up.
For that matter, would it not be just as useful to have hands with two thumbs and a single central finger?
