According to a chap named Charlie Darwin, Mankind is so unstable a species that he may one day become obsolete. Because Man will be unable to adapt to the rapid changes he himself has created, several hundred years from now this will be a world ruled by sharks, cockroaches, and other more adaptable sorts.
But all is not lost! This game is an exercise in controlling genetic drift, and insuring that we continue to be surrounded by friendly species. Zap the unstable life forms that threaten you and mutate them into friendly life forms that assure our mutual safe passage into the next age.