At present, and as far back as history or tradition enables us to trace, mankind has, as in the case of other animals, been very much restricted to definite geological provinces. Thus in the extreme case of the fair white and the Negro, the former cannot live and propagate its type south of the parallel of 40°, or the latter north of it. This argument was no doubt pushed too far by Agassiz, who supposed the whole world to be divided into a number of limited districts, in each of which a separate creation both of men, animals, and plants had taken place suited to the environment. This is clearly inconsistent with facts, but there is still some force in it when stripped of exaggeration, and confined to the three or four leading types which are markedly different. Especially it bears on the argument, on which monogenists mainly rely, of the peopling of the earth by migration from one common centre. No doubt migration has played a very great part in the diffusion of all animal and vegetable species, and their zoological provinces are determined very much by the existence of insurmountable barriers in early geological times. No doubt also man is better organized for migration than most other terrestrial animals, and history and tradition show that in comparatively recent times he has reached the remotest islands of the Pacific by perfectly natural means. But this does not meet the difficulty of accounting, if we place the origin of man from a single pair anywhere in the northern hemisphere, for his presence in palæolithic times in South Africa and South America. How did he get across the equatorial zone, in which only a tropical fauna, including the tropical Negro, can now live and flourish? Or _vice versâ_, if the original Adam and Eve were black, and the Garden of Eden situated in the tropics, how did their descendants migrate northwards, and live on the skirts of the ice-caps of the glacial period? Or how did the yellow race, so tolerant of heat and cold, and of insanitary conditions, and so different in physical and moral characters from either the whites or the blacks, either originate from them, or give rise to them? The nearest congeners of man, the quadrumana, monkeys and apes, are all catarrhine in the Old World, and all platyrhine in America. Why, if all are descended from the same pair of ancestors, and have spread from the same spot by migration? We can only reconcile the fact that it is so with the facts of evolution, by throwing the common starting-point or points of the lines of development much further back into the Eocene, or even further; and if this be true for monkeys, why not for man?