Given equal conditions, similar environment, the human race, wheresoever on this globe its lot be cast, shows a marked sameness in its traits and habits. This need not, in fact does not, argue a unity of origin. There is no reason why a custom may not be indigenous in many parts of the world, among peoples labouring under like conditions; and if the same customs be evolved the same cultural types will also be found to exist. Thus it is easy to find even striking resemblances between these Indians of Amazonia and such distant peoples as the Arunta of Central Australia, the cannibal tribes of pagan Malay, or, to go even wider afield, the Basque people of Southern Europe. This does not for a moment suggest that such common beliefs, customs, or cultures have been introduced from one to the other, or even borrowed from a common stock. The human mind seems to work broadly on certain definite planes of thought, and there is less mental difference between the low-type illiterate of a London slum and the denizens of a tropical forest than there is between him and the learned occupant of a University Chair, though both be nominally of the same nation.

Attempts are continually made to evolve some working classification of the South American Indians. The main difficulty, the sparsity of common factors, despite general similarity, is due in a measure at least to the absence of any standard, any fixity of language, or any confederation between the units of these races.