I shall illustrate this point by the discussion of a design found widely spread among the Indians of North America. Their decorative art is characterized by the use of straight lines, triangles and rectangles that appear in manifold combinations. One of the most typical forms is that of an isosceles triangle with enclosed rectangle, sometimes provided with spurs at the base (fig. 117). This design is found in an extended area. It occurs most frequently on the great plains but also on part of the western plateaus and among the Pueblo Indians (fig. 118). To the west it is found among the tribes of the woodlands and certain peculiar patterns of New England and the interior of Labrador are strongly reminiscent of it. The stylistic similarity, or better, identity of the pattern on the plains is so great that it cannot possibly have developed from several independent sources. It is part and parcel of the general art style of the area that has developed either in one spot, or what seems more probable, by the conflux of artistic activities of a number of tribes. Thirty or forty years ago, under the strong influence of the evolutionary theory, the psychologising ethnologist might have interpreted this similarity as due to the sameness of the reaction of the human mind to the same or similar environmental causes,—as Daniel G. Brinton explained the similarity of Algonquin and Iroquois mythologies. However, the development of our science since that time has so firmly established the fact that even the most primitive cultures must be considered as having had a historical development no less complex than that of civilization, that the theory of independent origin of almost identical phenomena in contiguous areas can no longer be maintained and has been given up by all serious students. [Illustration: Fig. 118. Triangular design, prehistoric Pueblo.]