1894.] Neo-Lamarckism and Neo-Darwinism. 663 
controlling factor or process in evolution is selective: the sur- 
vival, in the struggle for existence, of those individuals which 
are best fitted to survive. But while this is the naked core of 
Darwinism, there are various correlative or incidental hypoth- 
eses attached to it. Darwin, for instance, accepted in some de- 
gree the views of Lamarck as to the importance of functional 
characters; he considered that sexual selection, or the choice ex- 
ercised in securing mates, is often an important factor in modi- 
fying species; he thought that variation is induced by the 
modifications of environment, or the “changed conditions of 
life ;” and he was a firm believer in the hereditability of ac- 
quired characters. It is round these two great hypotheses— 
the functional or Lamarckian on the ohe hand, and the select- 
ive or Darwinian upon the other—in various forms and modi- 
fications, that the discussions of the philosophy of organic 
nature are at present revolving. 
Before leaving the subject of Darwinism, I wish to touch 
upon Darwin’s view of the cause of variation and his belief in 
the transmission of acquired characters. We shall presently 
see that the rehabilitation of the theories of Lamarck, under 
the name of Neo-Lamarckism, is undertaken, very largely, for 
the purpose of assigning the origin of variations to external . 
causes, or to the environment, in opposition to those who con- 
sider the source of variation to be essentially innate or at least 
internal. But Darwin also believed that variation is induced 
by the environment, and the chief factor in this environment, 
so far as its reaction upon the organism is concerned, is prob- 
ably excess of food supply, although climate, and other im- . 
pinging circumstances, are potent causes of modification. He 
marshalled arguments to support “the view that variations of 
all kinds and degrees are directly or indirectly caused by the 
conditions of life to which each being, and more especially its 
ancestors, have been exposed,” and that “ each separate varia- 
tion has its own proper exciting cause.” I do not understand 
how it has come about that various writers declare that Dar- 
win did not believe explicitly in the external cause of variation, 
and that they feel obliged to go back to Lamarck in order to — vd 
find a hypothesis for the occasion. It is true that Darwin be- - = 
