1. Parallel and Divergent Variation.—Evolutionists are familiar with these two forms of progressive variation in the organic world. They are equally evident in human progress.
No fact in ethnology is more striking than the parallelisms of primitive culture. Go where we will among the savage tribes of the globe, we find them developing the same arts along the same lines, framing their tribal organisations on the same models, calling in similar words on the same gods. Not only in this but in what seem matters of caprice, fancy, and local colour, the same similarity, almost identity, prevails. They tell stories of like plots, decorate their weapons in like patterns, dance and sing in like forms.
Yet, though so much alike, so “tarred with the same stick,” each tribe and group is different. Each has its own imprint and character. Each has its points of individuality.
This is “divergent” variation, just as universal, just as inevitable as the parallelism we have been considering. This extends into minute and seemingly unimportant details. We may, for example, compare the stone axes of neighbouring American tribes. In a casual survey, they look alike; a close inspection reveals slight but constant differences. The trained eye can distinguish their place of origin without difficulty.
This inherent divergence is so profound that two well-marked groups become incapable of mental unity. They may be separated by an imaginary line, and have been for generations under like climatic and cultural conditions, but the imprint of the divergence is ineradicable. If they have the same religion, they will understand it differently; the same events will impress them differently; their feeling and their hopes will be asunder.
While this is true, it is also true that a new stimulus to progress is created by the union of divergent lines of thought. The resultant is a fresh element in mental life, a new birth independent of either parent.
Such unions are brought about either by similarity or contrast. There is a species of elective affinity between certain lines of psychical development which at once unites them as they approach each other.
There is also a similar union induced by contrasted psychical states. We say familiarly that “opposites attract each other,” and it is a maxim drawn from frequent experience. The rapid changes from social freedom to military tyranny in the mercurial population of some states seem more gratifying to the ethnic spirit than a continued stable government.
Parallel variations lead to similarity in products. They are “homoplastic,” to use the term of the evolutionist. Primitive tribes, developing under the same general conditions of environment, are strikingly alike in culture.
Divergent variations are “heteroplastic,” that is, they lead to new products, and hence are the higher activities in all that makes for advancement. Whatever multiplies them stimulates the growth of culture.