continent before Columbus.
The decrease of natives following the Spanish conquest of tropical America has long been one of the most striking events of history. Popular historians sometimes speak as if most of the native population had been killed off by the cruelty of the conquistadores. Surely such talk could not proceed from those who are familiar with the action of natural selection. It is obvious that when the Spaniard brought the natives together, making them work in mines and assemble in churches, he brought them under conditions especially favorable for infection by the new diseases which he had brought. The aborigines of the New World, up to the time the Spaniards came, had undergone no evolution whatever against these diseases; consequently the evolution began at so rapid a rate that in a few centuries only those who lived in out-of-the-way places remain unscathed.
The same story is repeated, in a survey of the history of the Pacific Islands. Even such a disease as whooping-cough carried off adults by the hundred. Robert Louis Stevenson has left a graphic picture12 of natural selection at work: