It's widely believed that the awesome Aztec civilization was wiped out during the 1500s by diseases introduced by Spanish Conquistadores. Eighty percent of that Central Mexican population died in the devestating epidemics that followed their arrival. Research by a pair of scientists, however, suggests that their fate was not a result of visitors from the New World. If their conclusions are correct, the same ting that killed the Aztecs could happen again in this century.