08 FOOT-NOTES TO EVOLUTION. 
To this the present writer does not care to add. Ac- 
cording to some writers, as Herbert Spencer, this inheri- 
tance is a prominent factor in evolution itself. Accord- 
ing to August Weismann, it is simply a myth invented 
to explain phenomena the causes of which are unknown. 
Most of the arguments on both sides, thus far, have 
been theoretical only, based on no inductive evidence, 
and in science arguments of this sort are without value. 
Both suppositions rest, as Prof. Henry Fairfield Os- 
born has said, less “in fact than the logical improbabili- 
ties of other theories.” “Certainly,” Professor Osborn 
goes on to say, “we shall not assist research with any 
evolution factor grounded upon logic rather than upon 
inductive demonstration. A retrograde chapter in the 
history of science would open if we should do so, and 
should accept, as established, laws which rest so largely 
upon negative reasoning. Darwin’s survival of the fit- 
test we may alone regard as absolutely demonstated as 
a real factor without committing ourselves as to the ori- 
gin of fitness. The (next) step is to 
recognise that there may be an unknown 
factor or factors which will cause quite 
as great a surprise as Darwin’s. The feeling that there 
is such first came to the writer in 1890, in considering 
the want of an explanation for the definite and appar- 
ently purposeful character of certain variations. Since 
then a similar feeling has been voiced by Romanes and 
others, and quite lately by Scott, but the most extreme 
expression of it has recently come from Dr. Driesch in 
the implication that there is a factor not unknown but 
unknowable! . . . We are far from finally testing or dis- 
missing these old factors, but the reaction from specula- 
tion upon them is itself a silent admission that we must 
reach out for some unknown quantity. If such does 
exist there is little hope that we shall discover it except 
The unknown 
factors. 
