If you need to brush up on your biology lessons from bygone school days, perhaps a review of what convergent evolution means is in order. It means that two species become more similar to each other over time; they acquire characteristics that were not present in their last common ancestor.
Typically, convergent evolution occurs because both species are being acted upon by a similar set of environmental pressures.
Over vast periods of time, vultures that had the most desirable qualities for aiding survival passed them on through reproduction. Meanwhile, those who were not so fit died out and ceased passing their genes on.
One example of convergence in vultures is the bald head (where they do not have normal feathers). Although diverse species of vultures have bald heads, the feather-less head developed separately in those species to serve the same purpose, which is to help the animals from becoming overheated.
