'Prosper'!='exist'. He claimed they existed. They did not, barring ancient people being some sort of bizarre near-super-human race which can laugh off protein and iodine deficiencies and parasite loads and early-childhood infections in a way modern people can only dream of.

This is the same problem you see when people solemnly pontificate about how many Einsteins are trapped in Africa/India and if only we would fund One Laptop Per Child we could unlock their potential...