14 Darwin and after Darwin. 
know the natural causes of many diseases ; but yet 
no one nowadays thinks of reverting to any hypo- 
thesis of a supernatural cause, in order to explain the 
occurrence of any disease the natural causation of 
which is obscure. The science of medicine being in 
so many cases able to explain the occurrence of 
disease by its hypothesis of natural causes, medical 
men now feel that they are entitled to assume, on the 
basis of a wide analogy, and therefore on the basis of 
a strong antecedent presumption, that all diseases are 
due to natural causes, whether or not in particular 
cases such causes happen to have becn discovered. 
And from this position it follows that medical men 
are not logically bound to entertain any supernatural 
theory of an obscure disease, merely because as yet 
they have failed to find a natural theory. And so it 
is with biologists and their theory of descent. Even 
if it be fully proved to them that the causes which 
they have hitherto discovered, or suggested, are in- 
adequate to account for all the facts of organic nature, 
this would in no wise logically compel them to vacate 
their theory of evolution, in favour of the theory of 
creation. All that it would so compel them to do 
would be to search with yet greater diligence for the 
natural causes still undiscovered, but in the existence 
of which they are, by their independent evidence in 
favour of the theory, bound to believe. 
In short, the issue is not between the theory of a 
supernatural cause and the theory of any one parti- 
cular natural cause, or sct of causes—such as natural 
selection, use, disuse, and so forth. The issue thus 
far—or where only the fact of evolution is concerned— 
is between the theory of a supernatural cause as 
