Importance of Selection 61 



could be regarded as a serious rival to it. That selection is a factor, 

 and a very powerful factor in the evolution of organisms, can no 

 longer be doubted. Even although we cannot bring forward formal 

 proofs of it in detail, cannot calculate definitely the size of the 

 variations which present themselves, and their selection- value, cannot, 

 in short, reduce the whole process to a mathematical formula, yet we 

 must assume selection, because it is the only possible explanation 

 applicable to whole classes of phenomena, and because, on the other 

 hand, it is made up of factors which we know can be proved actually 

 to exist, and which, if they exist, must of logical necessity cooperate 

 in the manner required by the theory. We must accept it because 

 the phenomena of evolution and adaptation must have a natural 

 basis, and because it is the only possible explanation of them 1 . 



Many people are willing to admit that selection explains adapta- 

 tions, but they maintain that only a part of the phenomena are thus 

 explained, because everything does not depend upon adaptation. 

 They regard adaptation as, so to speak, a special effort on the part 

 of Nature, which she keeps in readiness to meet particularly difficult 

 claims of the external world on organisms. But if we look at the 

 matter more carefully we shall find that adaptations are by no means 

 exceptional, but that they are present everywhere in such enormous 

 numbers, that it would be difficult in regard to any structure what- 

 ever, to prove that adaptation had not played a part in its evolution. 



How often has the senseless objection been urged against selection 

 that it can create nothing, it can only reject. It is true that it can- 

 not create either the living substance or the variations of it; both 

 must be given. But in rejecting one thing it preserves another, 

 intensifies it, combines it, and in this way creates what is new. 

 Everything in organisms depends on adaptation ; that is to say, 

 everything must be admitted through the narrow door of selection, 

 otherwise it can take no part in the building up of the whole. But, 

 it is asked, what of the direct effect of external conditions, tempe- 

 rature, nutrition, climate and the like ? Undoubtedly these can give 

 rise to variations, but they too must pass through the door of selec- 

 tion, and if they cannot do this they are rejected, eliminated from 

 the constitution of the species. 



It may, perhaps, be objected that such external influences are 

 often of a compelling power, and that every animal must submit to 

 them, and that thus selection has no choice and can neither select 

 nor reject. There may be such cases ; let us assume for instance 

 that the effect of the cold of the Arctic regions was to make all the 

 mammals become black ; the result would be that they would all 



1 This has been discussed in many of my earlier works. See for instance The All- 

 Sufficiency of Natural Selection, a reply to Herbert Spencer, London, 1893. 



