SOME ASPECTS OF ZOOLOGY 33 



I have been taking the fact of evolution for granted, but 

 really we know Little or nothing about it at first hand. It is 

 properly called a doctrine ; that is, something taught ; and in 

 this case the thing taught is a very wide generalisation founded 

 upon evidence culled from comparative anatomy, comparative 

 embryology, palaeontology, geographical distribution and, 

 finally, upon breeding and experiment, all of which are pro- 

 vinces of the great subject of zoology. We believe the doctrine 

 to be true because the evidence derived from all these sources 

 is consistent and points to the same conclusion. 



Time forbids my maldng an attempt to outHne the evidence 

 afiorded by even one of these sources, but I wish to emphasise 

 the point that, although the doctrine is highly abstract and the 

 product of our reason, the evidence upon which we rely is 

 sohd concrete fact, and that the whole edifice of our reasoning 

 would collapse if it could be shown that the facts point to any 

 other conclusion. 



Evolution is not a process that we can see going on before 

 our eyes. It is an interpretation of marks that we see every- 

 where, but it may not be the right interpretation. If we are 

 to accept it, we must be able to represent clearly to our minds 

 the manner and course of evolution and the natural laws 

 governing it. For clearly the marks that we see are the result 

 of the operation of forces which we have to seek out and 

 understand. 



As is well known, there were evolutionists long before 

 Darwin, but the theory only found acceptance when he and 

 Wallace gave an intelhgible account of the interactions of 

 certain recognised natural phenomena and demonstrated that 

 they gave a credible explanation of the marks in question. 



I have avoided using the term natural laws because I am by 

 no means clear that the theory of the evolution of species by 

 the agency of Natural Selection can properly be called a law, 

 that is to say, a statement of invariable sequences. 



Using the most general terms, the theory of Natural 

 Selection asserts that progression and regression in the 

 scale of organisation are the outcome of competition among 

 animals for the means of subsistence. If this be absolutely 



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