THE LOGIC OF DARWINISM 533 



the able author of a little book on "Organic Evolution," written 

 a few years since for the instruction of the public, makes the 

 admission, in replying to objectors, that " we have not seen 

 natural selection at work"; and he propounds the opinion that, 

 for final proof, we have to await the result of certain observa- 

 tions then being made by Prof. Weldon on crabs in Plymouth 

 Sound, which he regards or regarded, as far as they had 

 proceeded at the time of writing, as " very nearly tantamount to 

 experimental proof of the theory of natural selection." Other 

 quotations which I shall subsequently make show that this 

 opinion is still commonly accepted. The point which I shall 

 here endeavour to establish is that this attitude of mind is 

 mistaken : that the Darwinian theory has long since received 

 the highest proof possible — the proof of experiment— and is 

 incapable of further verification, except in the sense in which 

 the theory of gravitation is still being verified by the continual 

 accumulation of additional instances in which the phenomena of 

 nature are found to conform with the law. 



Experiment differs from ordinary observation only in this, 

 that the phenomena observed are as far as possible kept under 

 control and isolated from the operation of the surrounding 

 forces of nature. Thus, instead of observing the effects pro- 

 duced by a particular acid upon a particular metal as these occur 

 in nature, which would be difficult if not impossible, we isolate 

 them both as far as possible and then bring them into contact 

 and observe their interaction. So, for instance, it is found that 

 the interaction of copper and sulphuric acid gives rise to the 

 beautiful blue vitriol of commerce. Now the domestication 

 of plants and animals, which began ages ago ; and the improve- 

 ment of breeds, which advanced gradually, in the course of 

 thousands of years, through unconscious to conscious selection, 

 until in recent times, especially since Darwin and Wallace 

 published their joint discovery, the deliberate improvement 

 of stock by selection of the most useful or most fancied strains 

 has become the common practice of every breeder : what are 

 these but the isolation and control of the phenomena of 

 reproduction in the organic world, attended as they are by 

 careful observation and usually by the maintenance, in modern 

 times, of a complete record of results ? What then does the 

 process amount to but one long series comprising an infinity of 

 individual experiments in proof of the Darwinian theory? Not 



