CHAPTER XVII 
THEORIES OF EVOLUTION: LAMARCK, DARWIN 
THE impression so generally entertained that the doctrine 
of organic evolution is a vague hypothesis, requiring for its 
support great stretches of the imagination, gives way to an 
examination of the facts, and we come to recognize that it is 
a well-founded theory, resting upon great accumulations of 
evidence. If the matter could rest here, it would be rela- 
tively simple; but it is necessary to examine into the causes 
of the evolutionary process. While scientific observation has 
shown that species are not fixed, but undergo transforma- 
tions of considerable extent, there still remains to be accounted 
for the way in which these changes have been produced. 
One may assume that the changes in animal life are the 
result of the interaction of protoplasm and certain natural 
agencies in its surroundings, but it is evidently a very diffi- 
cult matter to designate the particular agencies or factors of 
evolution that have operated to bring about changes in spe- 
cies. The attempts to indicate these factors give rise to differ- 
ent theories of evolution, and it is just here that the contro- 
versies concerning the subject come in. We must remember, 
however, that to-day the controversies about evolution are 
not as to whether it was or was not the method of creation, 
but as to the factors by which the evolution of different 
forms was accomplished. Says Packard: ‘We are all evo- 
lutionists, though we may differ as to the nature of the 
efficient causes.”’ 
Of the various theories which had been advanced to 
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