358 REVIEWS 
mutable, and as the whole science of natural history was constructed 
on the idea of their immutability, a complete readjustment of the 
science has resulted. With the revolution of thought started by 
Darwin’s “Origin of Species,” came a new conception of the nature 
of species. ‘The change was a philosophical one; no longer was the 
species considered to be a permanent entity with definite boundaries, 
but in the definition of organic species its time-relations and _ its 
geographical distribution were elements added to those of its mor- 
phology and physiology. This was a great advance. The organism 
came to be recognized not as a mere concrete being independent and 
standing by itself, constituted at the beginning what it is and remain- 
ing so during its existence, but as a very dependent part of a greater 
organism, nature itself, and related intimately with its surroundings or 
environment, to the organisms which preceded it or its ancestry, and 
to those which are to follow it or its descendants, as a sensitive, 
slowly changing reflex of all that has been and is. In the new con- 
ception there is the dim outlining of the idea (an old idea, but one 
which is day by day growing more distinct and of fuller com- 
prehension) that nature itself is a greater organism in which the 
species is but one of the organs.” 
The problem of the origin of species came to be a question for 
scientific investigation, only when the old idea that variations were not 
cumulative, but were always simply variations, was superseded by the 
newer idea that variations are cumulative, and that reproduction is not 
a process of exact but of inexact repetition of characters. Variability 
is thus assumed to be an inherent characteristic of all organisms. The 
natural inference from the Darwinian explanation of the origin of 
species is that characters appearing first as varieties are through con- 
tinuous repetition in the process of generation, gradually elevated to 
specific, generic, family, etc., rank. Paleontologists are inclined to 
doubt the fact of natural selection playing such an all-important part 
in the evolution of organisms. Cope has expressed the idea that 
evolution of generic characters has progressed in a different way, and 
has developed the idea of the law of acceleration and retardation 
which acts in association with natural selection but independent of it. 
There is assumed to be a special developmental growth force which is 
exhibited in variation itself and which becomes effective, as phylogenetic 
evolution, through acceleration and retardation. The Darwinian or 
natural selection school of evolutionists is engaged in accounting for 
