Many players have assumed that the mutants are more or less undead and, in thrall to El Dorado, exist only to kill those who approach the idol. The actual concept, however, is that while the virus certainly has a devolving effect on those infected, it does not entirely rob them of their cognitive faculties...or, more pressingly, their reproduction ability. The creatures that Nate encounters in Drake's Fortune are not the original Spaniards, but the eventual sions of their mutated lineage. The totems Nate encounters on the island (and, later, the traps constructed in part with the wreckage of his plane) were actually created by the Descendants.