Furthermore, the most intricate and apparently illogical ideas, and the most curious and complex customs, appear among a few tribes here and there in such a manner that the assumption of a common historical origin is excluded. When studying the culture of any one tribe, more or less close analogues of single traits of its culture may be found among a great diversity of peoples. Instances of such analogues have been collected to a vast extent by Tylor, Spencer, Frazer, Bastian, Andree, Post, and many others, so that it is not necessary to give here any detailed proof of this fact. A few examples will suffice. Among the more general ideas, I may mention the belief in a land of the souls of the deceased, located in the west, and reached by crossing a river,—known to all of us from Greek mythology, but well known also among the native tribes of America and Polynesia. Another example is the idea of a multiplicity of worlds,—one or more spanned over us, others stretching under us, the central one the home of man; the upper or lower, the home of the gods and happy souls; the other, the home of the unhappy,—an idea familiar to us from the positions of heaven and hell, but no less developed in India, Siberia, and arctic America. The idea of the ability of man to acquire protecting guardian spirits offers another example. Another domain of mental life furnishes equally striking instances. The universal knowledge of the art of producing fire by friction, the boiling of food, the knowledge of the drill, illustrate the universality of certain inventions. Still other phenomena of this class are furnished by certain elementary features of grammatical structure, like the use of expressions for the three persons of the pronoun,—namely, the speaker, the person addressed, and the person spoken of,—or the frequent distinction of singularity and plurality. Special curious analogues that occur in regions far apart may be exemplified by such beliefs as the possibility of foretelling the future by the cracking of burnt bones (Andree), the occurrence of the Phaëton legend in Greece and northwest America (Boas), the bleeding of animals by the use of a small bow and arrow (Heger), the development of astrology in the Old World and the New, the similarity of basketry technique and design in Africa and America (Dixon), the invention of the blow-gun in America and Malaysia. These examples will suggest the classes of phenomena to which I refer. It follows from these observations that when we find analogues of single traits of culture among distinct peoples, the presumption is, not that there has been a common historical source, but that they have arisen independently; and the theory suggests itself that a common cause accounts for the constant recurrence of these phenomena among the most varied members of mankind, no matter to what race they may belong.