16 Darwin, and after Darwin. 
natural causation. This conception of the uniformity 
of nature is one that has only been arrived at step by 
step through a long and arduous course of human 
experience in the explanation of natural phenomena. 
The explanations of such phenomena which are first 
given are always of the supernatural kind ; it is not 
until investigation has revealed the natural causes 
which are concerned that the hypotheses of super- 
stition give way to those of science. Thus it follows 
that the hypotheses of superstition which are the latest 
in yielding to the explanations of science, are those 
which refer to the more recondite cases of natural 
causation ; for here it is that methodical investigation 
is longest in discovering the natural causes. Thus it 
is only by degrees that fetishism is superseded by 
what now appears a common-sense interpretation of 
physical phenomena; that exorcism gives place to 
medicine ; alchemy to chemistry ; astrology to astro- 
nomy ; and so forth. Everywhere the miraculous is 
progressively banished from the field of explanation 
by the advance of scientific discovery; and the places 
where it is left longest in occupation are those where 
the natural causes are most intricate or obscure, and 
thus present the greatest difficulty to the advancing 
explanations of science. Now, in our own day there 
are but very few of these strongholds of the mira- 
culous left. Nearly the whole field of explanation is 
occupied by naturalism, so that no one ever thinks of 
resorting to supernaturalism except in the compara- 
tively few cases where science has not yet been able to 
explore the most obscure regions of causation. One 
of these cases is the origin of life ; and, until quite 
recently, another of these cases was the origin of 
