The Evolution hypothesis 455 
in a variety of forms. It has made idealistic thinkers revise their 
relation to the real world; it has led positivistic thinkers to find a 
closer connection between the facts on which they based their 
views ; it has made us all open our eyes for new possibilities to arise 
through the prima facie inexplicable “spontaneous” variations which 
are the condition of all evolution. This last point is one of peculiar 
interest. Deeper than speculative philosophy and mechanical science 
saw in the days of their triumph, we catch sight of new streams, 
whose sources and laws we have still to discover. Most sharply does 
this appear in the theory of mutation, which is only a stronger 
accentuation of a main point in Darwinism. It is interesting to 
see that an analogous problem comes into the foreground in physics 
through the discovery of radioactive phenomena, and in psychology 
through the assumption of psychical new formations (as held by 
Boutroux, William James and Bergson). From this side, Darwin’s 
ideas, as well as the analogous ideas in other domains, incite us to 
renewed examination of our first principles, their rationality and 
their value. On the other hand, his theory of the struggle for 
existence challenges us to examine the conditions and discuss the 
outlook as to the persistence of human life and society and of the 
values that belong to them. It is not enough to hope (or fear ?) 
the rising of new forms; we have also to investigate the possibility 
of upholding the forms and ideals which have hitherto been the bases 
of human life. Darwin has here given his age the most earnest and 
most impressive lesson. This side of Darwin’s theory is of peculiar 
interest to some special philosophical problems to which I now pass. 
TV. 
Among philosophical problems the problem of knowledge has in 
the last century occupied a foremost place. It is natural, then, to 
ask how Darwin and the hypothesis whose most eminent repre- 
sentative he is, stand to this problem. 
Darwin started an hypothesis. But every hypothesis is won by 
inference from certain presuppositions, and every inference is based 
on the general principles of human thought. The evolution™thypo- 
thesis presupposes, then, human thought and its principles. And 
not only the abstract logical principles are thus presupposed. The 
evolution hypothesis purports to be not only a formal arrangement of 
phenomena, but to express also the law of a real process. It supposes, 
then, that the real data—all that in our knowledge which we do not 
produce ourselves, but which we in the main simply receive—are 
subjected to laws which are at least analogous to the logical relations 
