NATURAL SELECTION V. ADAPTATION. 



7a 



Speaking of variations arising under cultivation and domesticity he says :* 

 " Man can neither originate varieties nor prevent their occurrence ; he can 

 only preserve and accumulate such as do occur. Unintentionally he 

 exposes organic beings to new and changing conditions of life, and 

 variability t ensues ; but similar changes of conditions might and do occur 

 under nature. Let it also be borne in mind how infinitely complex and 

 close-fitting are the mutual relations of all organic beings to each other 

 and to their physical conditions of life ; and consequently ivhat infinitely 

 varied diversities of structure might be of use to each being under chang- 

 ing conditions of life. Can it then be thought improbable, seeing that 

 variations useful to man have undoubtedly occurred, that other variations 

 useful in some way to each being in the great and complex battle of life 

 should occur in the course of many successive generations ? If such do 

 occur, can we doubt (remembering that many more individuals are born 

 than can possibly survive) that individuals having any advantage, however 

 slight, over others would have the best chance of surviving and of pro- 

 creating their kind ? On the other hand, we may feel sure that any 

 variation in the least degree injurious would be rigidly destroyed. This 

 preservation of favourable individual differences and variations and the 

 destruction of those which are injurious I have called Natural Selection,, 

 or the ' Survival of the Fittest.' " i I have italicised three sentences : the 

 first to emphasise the introduction by Darwin of the word " structure," 

 upon which alone varieties and species are based, into Malthus' theory ;. 

 an element which he never contemplated at all. Moreover, the destruc- 

 tion, when variations are supposed to arise to which Darwin refers, takes 

 place in infancy only, that is, before any varietal or specific characters 

 as a rule exist, because if the individual reaches maturity or the adult 

 stage, as when flowers and fruits are borne by plants, such have been 

 thereby "selected," so that any "beneficial or favourable characters" 

 which Darwin supposed to be able to determine the survival are non- 

 existent when the destructive period occurs. 



The last two italicised sentences in the passage quoted are purely- 

 hypothetical, for " injurious " variations are not known to occur. Hence 

 these sentences may be struck out, and what then remains ? 



That all the variations are more or less in harmony with the new con- 

 ditions of life. Hence natural selection as a means in securing the 

 " origin of species " on variations of structure drops out of sight, and is 

 relegated to its proper sphere of merely registering, so to say, what lives 

 and what dies under any special conditions of life. 



Notwithstanding his having introduced the word "structure," with- 

 out which there can be no new variety or species, Darwin constantly refers 

 to "constitution" as the, perhaps, most important element in deciding 

 whether a young organism shall survive or perish under the early struggle 

 for life; but "constitution" does not indicate or have anything to do 

 with variations of structure upon which "varieties" and "species" are 

 based. 



* Origin of Species, 6th ed., p. 62. 



f Darwin constantly uses " variability," which means the " ability " to vary, for 

 " variations." 



\ This term was suggested by Mr. Herbert Spencer. 



