GENERAL ZOOLOGY 



of evolution. In 1830, a year after Lamarck's death, a debate was held in 

 the French Academy in which Saint-Hilaire (1772-1844) upheld the 

 Lamarckian doctrines against Cuvier. Despite his opposition to the idea of 

 evolution, Cuvier had been forced to admit the differences between animals 

 of the past and those of the present, differences which could not exist if 

 animals had been originally created in their present form and had not 

 changed. Therefore, Cuvier had espoused the Doctrine of Cataclysms, which 

 assumed not one but a series of creations, each followed by a cataclysm that 

 destroyed all life. By supposing that each successive creation was on a 

 higher level than the preceding, it was possible to explain the succession of 

 types appearing in the fossil record. But the work of the geologists, culminat- 

 ing in Lyell's Principles of Geology (1830), showed that there was no evidence 

 for cataclysms. The period between 1830 and 1859, during which Darwin 

 was engaged in the studies summarized in his book, The Origin of Species, was 

 one of relative quiescence for the evolutionary theory. There was much 

 popular interest in the subject, however, as shown by the large sales of Robert 

 Chambers' book. The Vestiges of Creation (1844). Cuvier won his debate with 

 Saint-Hilaire, but in 1830 the case was already settled in favor of evolution, 

 as subsequent developments showed. 



Charles Darwin (1809-1882) began his studies 20 years before the publica- 

 tion of his famous volume. The fact that he was interested in determining 

 whether species originated by creation or transmutation (that is, evolution) 

 shows that the question was then under discussion. The idea seemed new in 

 1859 only because the evidence was so ably presented by Darwin and so 

 rapidly accepted by scientists and others. From our present point of view, 

 it is difficult to understand why biologists failed to recognize at an earlier 

 date the evidence for organic evolution — evidence that had been steadily 

 accumulating since the work of Buffon (1749), and that was sufficient to 

 justify acceptance of the concept 20 years before 1859. Nevertheless, Darwin 

 deserves his fame because it was he who brought about the acceptance of the 

 evolutionary doctrine. His Origin oj Species was a masterful summary and 

 extension of the evidence for organic evolution as an historic fact. Its 

 publication marked the beginning of a new epoch in human thought, as well 

 as in biological science. 



Explanation oj Darwin s Theory. In addition to bringing together and ex- 

 tending the evidence for the reality of organic evolution, Darwin proposed 

 as a major factor in the origin of species, and hence in evolution, what he 

 called natural selection. The principles of natural selection were inde- 

 pendently recognized by Alfred Russel Wallace in 1858. As conceived by 

 Wallace and Darwin, these principles may be summarized as follows. 

 Organisms possess an innate capacity for unlimited increase in numbers, but 

 under normal conditions populations remain approximately stationary. The 

 limitations on increase reflect a struggle for existence on the part of the 

 organism. In every population, random heritable variations occur in the 

 characteristics of organisms; these are not imposed or evoked by any action 



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