CREATION BY EVOLUTION
common than large ones. Dozens of different faint gradations in the color of the eye have appeared. Physiological changes so slight that they can be perceived only after long experimental study have been noted in great numbers. Every feature of the animal has thus become modified in many different ways. Hundreds of diverse races of Drosophila have taken origin from the original one; and many of these are more diverse than what have been called different species in this genus.
We do not yet understand the causes of these changes; we do not know how they are produced. An immense deal remains to be learned about them. But our ignorance must not be allowed to obscure the great, the essential fact that appears in these attempts to see evolution in progress—the fact of actual change. Remember that there are two opposite doctrines. One holds that the constitution of organisms is permanent; that they were created as they are and do not change. The other, the doctrine of evolution, holds that the hereditary constitution slowly changes as generations pass; that a single race differentiates in the course of time into diverse ones; that from one stock many are produced. The critical observations that have been made on these minute living organisms through the passage of generations substantiates this theory; they do change and differentiate into diverse races as generations pass. The facts observed are what the doctrine of evolution demands, not what the opposed theory demands.
REFERENCES
Note: A full, illustrated account of the studies of evolutionary change in Difflugia is given in an article entitled “Heredity, Variation, and the Results of Selection in the Uniparental Reproduction of Difflugia corona,” by H. S. Jennings, published in Genetics, vol. 1, 1916, pp. 407–534. A comparative account of these
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