762 THE PRINCIPLES OF SCIENCE. [CHAP 



institutions and characters. In order that a living form 

 shall continue to exist and propagate its kind, says Darwin, 

 it must be suitable to its circumstances, and the most 

 suitable forms will prevail over and extirpate those which 

 are less suitable. From these fruitful ideas are developed 

 theories of evolution and natural selection which go far 

 towards accounting for the existence of immense numbers 

 of living creatures plants, and animals. Apparent adap- 

 tations of organs to useful purposes, which Paley regarded 

 as distinct products of creative intelligence, are now seen 

 to follow as natural effects of a constantly acting tendency. 

 Even man, according to these theories, is no distinct crea- 

 tion, but rather an extreme case of brain development. 

 His nearest cousins are the apes, and his pedigree extends 

 backwards until it joins that of the lowliest zoophytes. 



The theories of Darwin and Spencer are doubtless not 

 demonstrated ; they are to some extent hypothetical, just 

 as all the theories of physical science are to some extent 

 hypothetical, and open to doubt. Judging from the 

 immense numbers of diverse facts which they harmonise 

 and explain, I venture to look upon the theories of evolu- 

 tion and natural selection in their main features as two of 

 the most probable hypotheses ever proposed. I question 

 whether any scientific works which have appeared since the 

 Principia of Newton are comparable in importance with 

 those of Darwin and Spencer, revolutionising as they do all 

 our views of the origin of bodily, mental, moral, and social 

 phenomena. 



Granting all this, I cannot for a moment admit that the 

 theory of evolution will destroy theology. That theory 

 embraces several laws or uniformities which are observed 

 to be true in the production of living forms ; but these laws 

 do not determine the size and figure of living creatures, any 

 more than the law of gravitation determines the magnitudes 

 and distances of the planets. Suppose that Darwin is 

 correct in saying that man is descended from the Ascidians : 

 yet the precise form of the human body must have been 

 influenced by an infinite train of circumstances affecting 

 the reproduction, growth, and health of the whole chain of 

 intermediate beings. No doubt, the circumstances being 

 what they were, man could not be otherwise than he is, and 

 if in any other part of the universe an exactly similar earth, 



