ORIGINAL: GMMAT
I guess natural selection figures in, here, as well. The slow ones.....the ones with sight problems......ones that don't hear well........the really curious ones.......die, first.
I think that is the primary factor. Wild animals would not survive very long with impared vision, particularly. Natural selection over a few millenia keeps them with good eyesight. A large chunk of the human pop has poor eyesight since it is no longer crucial to our survival.