2. Variation in Circles or Curves.—Both parallel and divergent evolution are expressions of continuity of progress in lines, extending from point to point, intersecting to produce other lines of new directions.
Such a rectilinear scheme is the simplest that we can sketch of human advancement; and for many purposes it is sufficiently correct. It does not, however, fully express the geometrical representation of such agencies as we are considering. Professor Baldwin has justly remarked that there is a “circular activity” in all progress. Its influence is not aimed solely at a point ahead, but extends itself in all directions. The reception of a new and true idea in the human mind may be likened to the introduction of a ray of sunlight into a darkened room. Its chief force is seen in the linear shaft of light, but the illumination extends in some degree to the whole space.
Johannes Schmidt has shown that the distribution of the early Aryan dialects and religions was not from the point of common origin by right lines of migration in different directions, but should be represented diagrammatically by a series of irregular circles and ellipses, overlapping each other. The tendency to variation arises in some centre and spreads from it in a series of curves. These meeting others lead to an “interlinking” of cultural areas.
This is true of the other elements of ethnic culture. The localities where many such overlappings occurred became secondary centres from which in turn the circular activity of culture was propagated.
A mart where many visitors from different nations congregated would receive some new learning from all and through its concentration would impart this higher potency in some measure to all. For example, the city of Nippur, on the Babylonian plain, attracted twenty-five hundred years ago to its markets not only Assyrians and Edomites, but Medes and Persians from the East, Syrians and Hittites from the West, and probably Greeks and Egyptians and Arabians from remoter lands.
Human progress has been likened by some to a spiral figure where each advance is a repetition of a former stage but with improvements to it. This is a combination of the right line and the curve; but the notion that repetition or recapitulation exists in evolution in any other form than that of renewed effort finds little support in natural science.
3. Variation in Waves, or Rhythmic Undulations.—Some of the most recent speculations on the ultimate forces of the universe lead to the belief that they are maintained in activity by an eternal rhythmic pulsation or undulation, generating its energy from its periods of repose.
This doctrine has been applied by Professor Gerland to the progress of the human race. His teaching is that after a period of rapid advance there follows one of depression, which in turn is succeeded by another of advance, reaching a higher development than any which preceded it.
Other writers have expressed this notion in the form that after a period of activity and invention follows one of repose and reflection, giving way in turn to another of activity.
The Rate of Progress.—Professor de Mortillet calculates from a wide range of data, geologic and archæologic, that man has lived on the earth about 240,000 years. The most conservative student of prehistoric records would not estimate the life of our species at less than fifty thousand years, and it is much more likely to be double that duration.