THEORIES OF LAMARCK AND DARWIN 369 
account for evolution, up to the announcement of the muta- 
tion-theory of De Vries in 1900, three in particular had 
commanded the greatest amount of attention and been the 
field for varied and extensive discussion. These are the 
theories of Lamarck, Darwin, and Weismann. They are 
comprehensive theories, dealing with the process as a whole. 
Most of the others are concerned with details, and emphasize 
certain phases of the process. 
Doubtless the factors that have played a part in molding 
the forms that have appeared in the procession of life upon 
our globe have been numerous, and, in addition to those that 
have been indicated, Osborn very aptly suggests that there 
may be undiscovered factors of evolution. Within a few 
vears De Vries has brought into prominence the ideaof sudden 
transformations leading to new species, and has accounted 
for organic evolution on that basis. Further consideration of 
this theory, however, will be postponed, while in the present 
chapter we shall endeavor to bring out the salient features 
of the theories of Lamarck and Darwin, without going into 
much detail a them. 
LAMARCK 
Lamarck was the first to give a theory of evolution that 
has retained a placc in the intellectual world up to the present 
time, and he may justly be regarded as the founder of that 
doctrine in the modern sense. The earlier theories were 
more restricted in their reach than that of Lamarck. Eras- 
mus Darwin, his greatest predecessor in this field of thought, 
announced a comprehensive theory, which, while suggestive 
and forceful in originality, was diffuse, and is now only of 
historical importance. The more prominent writers on evo- 
lution in the period prior to Lamarck will be dealt with in 
the chapter on the Rise of Evolutionary Thought. 
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