WHAT IT IS AND WHAT IT IS NOT. 65 
usually associated with the recognition of natural selec- 
tion as the great motive power in organic change. 
Darwinism was at first regarded as a “working hypoth- 
esis.” It is now an integral part of biological science, 
because all opposing hypotheses have long since ceased 
to work. It is as well attested as the theory of gravita- 
tion, and its elements are open to less doubt. All in- 
vestigations in biology must assume it, as without it 
most such investigations would be impossible. Natural- 
ists could no more go back to the old notion of special 
creation for each species and its organs than astrono- 
mers could go back to the old notion of guiding angels 
as directors of planetary motion. Without the theory 
of organic development through natural selection the 
biological science of to-day would be impossible. 
In a third sense the word evolution is applied toa 
method of investigation. It is the study of present con- 
ditions in the light of the past. The 
preliminary work of science is the de- 
scriptive part. This involves accuracy 
of observation and precision of statement, but makes 
no great demands on the powers of logical analysis and 
synthesis. The easy work of science is largely already 
done. Those who would continue investigation must 
study not only facts and structures, but the laws that 
govern them. In the words of John Fiske, “ Whether 
planets or mountains or molluscs or subjunctive modes 
or tribal confederacies be the things studied, the scholars 
who have studied them most fruitfully were those who 
have studied them as phases of development. Their 
work has directed the current of thought.” The most 
difficult problems in life are susceptible of more or less 
perfect solution if approached by the method of evolu- 
tion. They can not be even stated as problems in any 
other terms. In every science worthy of the name the 
Evolution as a 
method of study. 
