CHAPTER FOUR 



Evide7ices of Evolution 

 III: Comparative Physiology 

 and Biochemistry 



For more than two centuries before Darwin, the great investigative 

 impetus derived from the Renaissance resulted in the accumulation of a 

 great store of biological knowledge. On the whole, however, it was a dis- 

 organized array of data, a burgeoning chaos, for there was no basic 

 biological principle which could integrate the whole field. The publication 

 of the "Origin" caused a revolution in biological thinking because it pro- 

 vided just such a principle, a rational framework upon which the grand 

 scope of biology could be organized. Its success in achieving this is one 

 of the strong arguments for evolution. The biolog)- of Darwin's time was, 

 however, almost exclusively morphological: physiology was in its infancy, 

 and biochemistry did not yet exist. Consequently, these fields were the 

 last to be influenced by the Darwinian revolution in biological thinking. 

 Yet many biologists regard the morphological traits with which we have 

 dealt thus far as simply the more obvious results of specific compounds 

 and processes. In short, thev feel that evolution is basically a biochemical 

 phenomenon. It is therefore significant that an array of very cogent evi- 

 dence for evolution has emerged from these fields. 



On the broadest possible level, there is the fact that protoplasm appears 

 to be basically one substance, varied in more or less minor ways from 

 species to species, throughout the living world. It contains very nearly 

 the same elements, compounded into roughly the same proportions of 

 proteins, carbohydrates, fats, water, and supplementary substances. The 

 most basic functions of protoplasm are describable in very similar terms, 

 with few exceptions, througliout the living world. That this should be true 

 is a very impressive fact. It is subject to otluu- interpretations, but it 

 strongly suggests communitv of origin, with the most fundamental prop- 

 erties of living things remaining rather constant, while variation in less 

 essential respects lias produced the immensely \'aried forms of the living 

 world. 



Much the same is the story with respect to the chemistry of the chromo- 

 somes, the physical basis of heredity, incompletely though it is known. 



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