CUMULATIVE EVIDENCE FOR EVOLUTION
studied facts are out of accord with the theory of evolution, and thousands upon thousands proclaim its truth. What more cogent proof of a theory can one ask?
An excellent example of the way in which unexpected discoveries in a new field have supported and confirmed the theory of evolution is seen in the new science of serology, or blood tests. Before anything was known about the specific chemical constitution of the blood, animals had been classified into phyla, classes, orders, families, genera, and species. The method used was the method of homology—that is, groups of animals that were most nearly similar in structural pattern, not only in the adult form but throughout the course of embryonic development, were believed to be most closely related and were placed in the same species. Animals differing in details but having the same general features were placed in the same genus, family, order, class, phylum, according to the degrees of their structural resemblance. A comprehensive system of classification has thus been built up that is believed to constitute a sort of pedigree, or ancestral tree, of animal life.
A decade or so ago an entirely new and highly refined method, quite unrelated to the method of homology, was devised for testing animal relationships. This is the so-called blood precipitation method, which depends upon the fact that the blood of an animal is a sort of quintessence of its chemical composition. Thus the blood of all human beings has a highly specific chemical constitution differing from that of all other species. The same is true of the blood of the dog, the horse, or any other animal. The degree of chemical resemblance and difference in the blood of different animals may be measured quantitatively with the greatest accuracy. Assuming, then, that the degree of chemical resemblance
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