On the other hand dynamic conditions exist, based on environment, physiological, psychological, and social factors, that may bring forth similar cultural processes in different parts of the world, so that it is probable that some of the historical happenings may be viewed under more general dynamic viewpoints. But historical data are not available and when prehistoric research does not reveal sequences of cultural changes, the only available method of study is the geographical one, the study of distribution. This has been emphasized in the last third of the past century by Friedrich Ratzel. It has probably been most rigidly developed in the United States. I illustrated this method in 1891 by a study of the distribution of folk-tales in North America[2] and it has become more and more the method of analytical study of cultural forms. [2] Journal of American Folk-Lore, Vol. IV, pp. 13-20; also Science, Vol. XII (1888), pp. 194-196. Its very fruitfulness, however, has led to extremes in its application that should be guarded against. I pointed out, in print in 1911 and often before and since that time in speaking, that there is a certain homology between universal distribution of cultural facts and their antiquity. The fundamental principle involved in this assumption was fully discussed by Georg Gerland in 1875,[3] although we are hardly ready to accept his conclusions. The data of prehistoric archaeology prove that some of these universal achievements go back to paleolithic times. Stone implements, fire and ornaments are found in that period. Pottery and agriculture, which are less universally distributed, appear later. Metals, the use of which is still more limited in space, are found still later. [3] Anthropologische Beiträge, Halle a/S, pp. 401 et seq.