4 INTRODUCTION. 



may select and preserve each successive variation, with the 

 distinct intention of improving and altering a breed, in accord- 

 ance with a preconceived idea ; and by thus adding up varia- 

 tions, often so slight as to be imperceptible by an uneducated 

 eye, he has effected wonderful changes and improvements. It 

 can, also, be clearly shown that man, without any intention 

 or thought of improving the breed, by preserving in each 

 successive generation the individuals which he prizes most, and 

 by destroying the worthless individuals, slowly, though surely, 

 induces] great changes. As the will of man thus comes into 

 play, we can understand how it is that domesticated breeds 

 show adaptation to his wants and pleasures. We can further 

 understand how it is that domestic races of animals and culti- 

 vated races of plants often exhibit an abnormal character, as 

 compared with natural species ; for they have been modified not 

 for their own benefit, but for that of man. 



In a second work I shall discuss the variability of organic 

 beings in a state of nature ; namely, the individual differences 

 presented 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 how difficult, 

 or rather how 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-sj)ecies 

 and true species. I shall further attempt to show that it is 

 the common and widely ranging, or, as they may be called, 

 the dominant species, which most frequently vary ; and that 

 it is the large and flourishing genera which include the greatest 

 number of varying species. Varieties, as we shall see, may 

 justly be called incipient species. 



But it may be urged, granting that organic beings in a state 

 of nature present some varieties, — that their organization is 

 in some slight degree plastic ; granting that many animals 

 and plants have varied greatly under domestication, and that 

 man by his power of selection has gone on accumulating such 

 variations until he has made strongly marked and firmly in- 

 herited races"; granting all this, how, it may be asked, have 

 species arisen in a state of nature ? The differences between 

 natural varieties are slight; whereas the differences are con- 



