About the time of the discovery of America, Europeans began to visit and colonize the tropics, but it was early discovered that the white man could not live and thrive with such conditions and surroundings as existed there. It seemed to be demonstrated that there was something in the climate that sapped his constitution and broke his health. This statement applies to white children to an even greater extent than to the adult. The great colonizing nations had been the Spaniards, the Portuguese, the Dutch, the French and the English. Their experience had all been exactly similar from the beginning of the sixteenth century to the present time—that the white man could not live and thrive in the tropics, nor could he leave behind him in those regions a healthy progeny. By all men everywhere it was believed that this was due to tropical climatic conditions, which could not be combated, and that therefore the white man was permanently barred from building up any great civilization in these regions. Man, like all other animals, must necessarily have developed in one locality. If we accept the modern explanation, generally received by educated persons, Darwinism, all life at present on the globe must have descended from one single cell. If we take some individual animal at present living, a dog, for instance, we could trace his ancestry back to the first cell, if we could obtain all the facts in the case. By very slow changes, genus after genus and species after species developed from this first cell, each genus and each species differing slightly from the one preceding. An individual varying very slightly from the other individual of his species, becomes the progenitor of a new species, provided the variation accords with his surroundings so as to fit him better for the struggle of life. But all of the new species must descend directly from the one pair which produces these favorable variations in their progeny. Every species, therefore, such as the dog, must originate in some one locality. If at any time this species of animal is found in all parts of the world, it must have slowly spread from the locality in which it originated. The dog, therefore, came to his present development in some one part of the world. As he is now found in all parts of the world, he must have spread from this one locality in which he originated.