THE EVOLUTIONARY CONCEPT 343 



Our knowledge of the causes and results of evolution has advanced far 

 since Darwin's time, as will become evident in what follows; but here 

 let us note that Darwin's demonstration of the fact of evolution assures 

 him a place among the outstanding scientists of all time and makes him 

 perhaps the greatest of biologists. Evolution and Darwinism are, however, 

 not the same thing. Evolution is a fact; Darwinism is a term used by 

 biologists to designate Darwin's own explanation of the occurrence of 

 evolution. His theory of natural selection has stood the test of time but 

 proves to be only a partial explanation. 



SUBSEQUENT MODIFICATION OF DARWINIAN THEORY 



Neither Darwin nor his immediate followers stressed the distinction 

 between the historical fact of evolution and the Darwinian concept of the 

 interplay of natural forces that brought it about. The first great debates 

 and controversies were fought out over the question of whether evolution 

 was a fact. Nearly all attacks on the proposed causal factors were inci- 

 dental, and with the establishment of the doctrine of the common descent 

 and blood kinship of organisms, the many lines of investigation opened to 

 study proved so fruitful of results and so illuminating for an understand- 

 ing of biological phenomena that the analysis of the evolutionary factors 

 was neglected. Biologists chiefly concerned themselves with new studies 

 and interpretations of the data of comparative morphology, embryology, 

 and distribution. A very strong impetus was also given to the search for 

 fossil evidence of earlier forms of life and to the tracing of actual evolu- 

 tionary lineages. 



Other theories of evolution were also recalled — earlier ideas that had 

 been suggested by the great French naturalists Buffon and Lamarck, but 

 ideas that had been dismissed and largely forgotten because the fact of 

 evolution itself was not accepted. Buffon had suggested that the obvious 

 differences between similar forms living in different climates and environ- 

 ments had been produced by direct and appropriate responses of the 

 organisms to their particular environments. Lamarck (and Darwin's own 

 grandfather, Erasmus Darwin) had developed the much more complete 

 and far-reaching theory that the use or disuse of any part of the body 

 resulted in the increased development or partial atrophy of that part, 

 that the changes thus produced in an individual were transmitted to the 

 offspring, and that if the same pattern of use or disuse were continued 

 for many generations, the changes would be accumulative and result in 

 marked modification. In Lamarck's view the stimulus for use or disuse 

 lay in the needs of an organism to cope with its particular environment. 

 This theory, presented in 1802 to 1809, came to be known as Lamarckism. 



