seem nearly always destined to die out, being supplanted by the descendants of simpler and more plastic forms. Supposing the career of man to resemble that of other specialized mammalia, he might be expected to have before him perhaps another hundred thousand years, and then in all probability the end of the world, so far as he was concerned with it as an animal. Even on this hypothesis, he would have as much occasion to prepare for his terrestrial future as a young child has for its adult life, but there are very good reasons for supposing that the fate of man need not necessarily be the same as that of the animals to which he is most nearly allied. Prior to the existence of man, living beings might have been divided roughly into two groups, those related to very simple or unchanging environments, such as the amoeba or the oyster, and those specially adapted to complex conditions, such as the yucca moth and the giraffe. The former have proved successful through their very simplicity, have been saved by their lack of progress; the latter are nature's masterpieces, often destined, as such things are, to go out of fashion. Any single man may be taken as a rather extreme example of the latter type; he is extraordinarily dependent upon a special set of conditions, but the race as a whole is relatively independent, and without sacrificing anything of its organic complexity, is able to meet and overcome the dangers which have destroyed so many of the higher mammals. If with this man can secure a genuine but moderate progress in his fundamental organism, not sufficient to break the continuity of tradition or destroy his essential specific unity, he may be assured a career such as no mammal ever had before.
The causes of the extinction of other animals have been principally related to climate, food and natural enemies, including here the germs of disease. With regard to climate, man at first, through racial differentiation, became adapted to everything from tropical heat to arctic cold; but here he was on the way to split up into a number of distinct species. Now through devices of housing and clothing he can almost create climatic environments for himself, and so single races, or mixtures of races, are to be found nearly everywhere. At the same time, like the bird, he knows how to migrate when necessary, so that he will never be destroyed by changes confined to a single continent or even hemisphere.
In the case of food, he is relatively unspecialized, and no doubt his omnivorousness has greatly aided his spread over the globe. So long as he had to depend upon the supplies furnished gratis by nature this was a necessary condition of his cosmopolitanism; but now that he can so largely control his food supply, and can carry any given product to the opposite end of the earth, it is a question whether there will not be a distinct gain in a return to primitive simplicity in diet.
Of natural enemies, the grosser and more tangible kind, like the
