420 
DARWINISM 
CHAP. 
elaboration that the outer and inner parts of these are 
necessarily subject to different conditions; and that the outer 
actions of air or "water lead to the formation of integuments, 
and sometimes to other definite modifications of the surface, 
whence arise permanent differences of structure. Although 
in these cases also it is very difficult to determine how much 
is due to direct modification by external agencies transmitted 
and accumulated by inheritance, and how much to spontaneous 
variations accumulated by natural selection, the probabilities 
in favour of the former mode of action are here greater, 
because there is no differentiation of nutritive and reproductive 
cells in these simple organisms ; and it can be readily seen 
that any change produced in the latter will almost certainly 
affect the next generation. 1 We are thus carried back almost 
to the origin of life, and can only vaguely speculate on what 
took place under conditions of which we know so little. 
The American School of Evolutionists. 
The tentative views of Mr. Spencer which we have just dis¬ 
cussed, are carried much further, and attempts have been made 
to work them out in great detail, by many American naturalists, 
whose best representative is Dr. E. D. Cope of Philadelphia. 2 
This school endeavours to explain all the chief modifications 
of form in the animal kingdom by fundamental laws of growth 
and the inherited effects of use and effort, returning, in fact, to 
the teachings of Lamarck as being at least equally important 
with those of Darwin. 
The following extract will serve to show the high position 
claimed by this school as original discoverers, and as having 
made important additions to the theory of evolution :— 
“Wallace and Darwin have propounded as the cause of 
modification in descent their law of natural selection. This 
law has been epitomised by Spencer as the ‘ survival of the 
fittest.’ This neat expression no doubt covers the case, but it 
leaves the origin of the fittest entirely untouched. Darwin 
assumes a ‘ tendency to variation ’ in nature, and it is plainly 
1 This explanation is derived from Weismann’s Theory of the Continuity 
of the Germ-Plasm as summarised in Nature. 
- See a collection of his essays under the title, The Origin of the Fittest : 
Essays on Evolution. D. Appleton and Co. New York. 1887. 
