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 dis- 

 coveries 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 classi- 

 fied 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 differ- 

 ing 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 chem- 

 ical 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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