8c THE SCIENTIFIC EVIDENCES OF 



to have witnessed the transmutation of species, 

 it follows that evolution has not been proved. 



Now, it is perfectly right to draw a clear 

 distinction between a theory and a demonstra- 

 tion ; but it is a great mistake to suppose that 

 a theory may then only be admitted by science 

 when it has been demonstrated. Bishop Butler 

 tells us that " Probability is the guide of life," 

 and not less true is it that probability is like- 

 wise the guide of science. The business of 

 science, as of common life, is to estimate 

 correctly the relative degrees of probability pre- 

 sented by this and that theory or hypothesis ; 

 when once a theory or hypothesis is demon- 

 strated it ceases to be a matter of scientific 

 inquiry, and becomes a matter of scientific fact. 

 Thus received, we have to consider the doctrine 

 of evolution as certainly standing in the first 

 rank of scientific theories in respect of proba- 

 bility sustained by evidence, although no less 



