380 BIOLOGY AND ITS MAKERS 
of his, writings and had incidentally corrected several erro- 
neous conception. 
Neo-Lamarckism.—The ideas of Lamarck regarding the 
beginning of variations have been revived and accorded much 
respect under the designation of Neo-Lamarckism. The 
revival of Lamarckism is especially owing to the palzon- 
tological investigations of Cope and Hyatt. The work of 
E. D. Cope in particular led him to attach importance to the 
effect of mechanical and other external causes in producing 
variation, and he points out many instances of use-inher- 
itance. Neo-Lamarckism has a considerable following; it 
is a revival of the fundamental ideas of Lamarck. 
DARWIN’S THEORY 
While Lamarck’s theory rests upon two sets of facts, 
Darwin’s is founded on three: vwis., the facts of variation, 
of inheritance, and of natural selection. The central feature 
of his theory is the idea of natural selection. No one else 
save Wallace had seized upon this feature when Darwin 
made it the center of his system. On account of the part 
taken by Wallace simultaneously with Darwin in announcing 
natural selection as the chief factor of evolution, it is appro- 
priate to designate this contribution as the Darwin-Wallacc 
principle of natural selection. The interesting connection 
between the original conclusions of Darwin and Wallace is 
set forth in Chapter XIX. 
Variation.—It will be noticed that two of the causes 
assigned by Darwin are the same as those designated by La- 
marck, but their treatment is quite different. Darwin (Fig. 
113)assumed variation among animals and plants without at- 
tempting to account for it, while Lamarck undertook to state 
the particular influences which produce variation, and al- 
though we must admit that Lamarck was not entirely suc- 
