What, then, is the difference between the civilization of the Old World and that of the New World? It is essentially a difference in time. The one reached a certain stage three thousand or four thousand years sooner than the other. Although much stress has been laid upon this greater rapidity of development in the Old World, I think that it is not by any means proof of greater ability of the races of the Old World, but that it is adequately explained by the laws of chance. When two bodies run through the same course with variable rapidity, sometimes quickly, sometimes slowly, their relative position will be more likely to show accidental differences, the longer the course which they run. Thus two infants a few months old will be much alike in their physiological and psychical development; two youths of equal age will differ much more; and two old men of equal age may, the one still be in full possession of his powers, the other on the decline, due mainly to the accidental acceleration or retardation of their development. The difference in period of development does not signify that the one is by heredity structurally inferior to the others. Applying the same reasoning to the history of mankind, we may say that the difference of a few thousand years is insignificant as compared to the age of the human race. The time required to develop the existing races is entirely a matter of conjecture, but we may be sure that it is long. We also know that man existed in the Eastern and Western Hemispheres at a time that can be measured by geological standards only. Penck’s recent investigations on the glacial age in the Alps have led him to the conclusion that the age of man must be measured by a span of time exceeding one hundred thousand years, and that the highly specialized civilization of the Magdalenian is not less than twenty thousand years old. There is no reason to believe that this stage was reached by mankind the world over at the same period, but we must assume as the initial point the remotest times in which we find traces of man. What does it mean, then, if one group of mankind reached the same stage at the age of a hundred thousand years as was reached by the other at the age of a hundred and four thousand years? Would not the life-history of the people, and the vicissitudes of its history, be fully sufficient to explain a delay of this character, without necessitating us to assume a difference in their aptitude to social development? (See Waitz.) This retardation would be significant only if it could be shown that it occurs independently over and over again in the same race, while in other races greater rapidity of development was found repeatedly in independent cases.