No such stories are told about the white settlements on this continent, even before the days of quarantine and scientific medicine. There is no other adequate explanation of the difference, than that the two races have evolved to a different degree in their resistance to these diseases. It is easily seen, then, that man's evolution is going on, at varying rates of speed, in probably all parts of the human race at the present time. We do not mean, of course, to suggest that all the natives who have died in the New World since the landing of Columbus, have died because the evolution of their race had not proceeded so far in certain directions as had that of their conquerors. But the proportion of them who were eliminated for that reason is certainly very large. In the more remote parts of South America the process is still going on. Recent press dispatches have carried the account of the University of Pennsylvania's Amazon Expedition, under the direction of William C. Farrabee. In a letter dated March 16, 1916, the leader told of the discovery of the remains of the tribe of Pikipitanges, a once populous tribe of which a chief, six women and two boys alone are left. The tribe had been almost wiped out, Dr. Farabee reported, by an epidemic of _influenza_! If the aborigines of the New World succumb to the diseases of the European, it is not less true that the European succumbs to diseases against which his race has not been selected. The deadliness of yellow fever to Americans in the tropics, and the relative immunity of Negroes, is familiar; so too is the frequently fatal result of the African tropical fevers on the white man, while the natives suffer from them much less, having been made more resistant by centuries of natural selection. This long discussion may now be summarized. We dealt with lethal selection, that form of natural selection which operates by prematurely killing off the less fit and leaving the more fit to survive and reproduce their kind. It is of course understood that the word "fit" in this connection does not necessarily mean morally or mentally superior, but merely fit for the particular environment. In a community of rascals, the greatest rascal might be the fittest to survive. In the slums of a modern city the Jewish type, stringently selected through centuries of ghetto life, is particularly fit to survive, although it may not be the physical ideal of an anthropologist.