DARWIN, AND THE ORIGIN OF SPECIES 189 



and Plants under Domestication," firmly planted the word vari- 

 ation in the literature of a generation which has forgotten that it 

 is a technical term; although any one who will make the attempt 

 will find few places, in this book, or in the "Origin of Species,'* 

 or in the writings of Wallace, where diversity may not be sub- 

 stituted for variatioji without changing the meaning; and although 

 Darwin has himself defined the word in the introduction to this 

 work ("Animals and Plants," Amer. ed., p. 14) in the promise 

 that " in a second work I shall discuss the variability of organic 

 beings in a state of nature, namely, the individual differences pre- 

 sented by animals and plants, and those slightly greater and 

 generally inherited differences which are ranked by naturalists 

 as varieties or geographical races." " We shall see," he says, 

 "how difficult, or rather impossible, it often is, to distinguish 

 between races and sub-species, as the less well-marked forms 

 have sometimes been denominated, and again between sub-species 

 and species." 



Now, as words are commonly used, the great practical differ- 

 ence between diversity and variation in this; that, while all admit 

 the infinite diversity of nature, variation is a dynamical change, 

 and is not held to be accounted for until a physical cause of the 

 change has been discovered. 



I cannot believe any one would have thought that natural 

 selection fails to account for the origin of species until we 

 discover some other explanation of the fitness of the varia- 

 tions which are selected, if Darwin and Wallace had not used 

 the word with this technical meaning; for we may admit that 

 living things do not differ from each other without cause, with- 

 out admitting that the physical causes of this diversity are 

 adaptive. 



The objection to natural selection which has thus arisen is 

 often formulated as an assertion that since natural selection does 

 not produce, but only preserves, the variations which are fittest, 

 it accounts for nothing in itself, since the real explanation of the 

 origin of species is to be sought in the "laws of variation" or 

 "causes of variation," which must, it is said, supply the raw 

 material for selection before this can be selected. 



As it is self-evident that natural selection originates nothing, 



