178 THE FOUNDATIONS OF ZOOLOGY 



tive, and soon reaches a maximum ; but this is no proof of any 

 "principle of organic stability," or anything else except the truth 

 that long ages of natural selection have made the organism such 

 a unit or coordinated whole that no great and continuous change 

 in one feature is possible, unless it be accompanied by general 

 or constitutional change. 



Nor must we forget that, in a state of nature, selection is not 

 for one feature, nor is it pedigree selection, or breeding from the 

 fittest. It is the extermination of the unfit, and unfitness may 

 come from the imperfect coordination of the whole, or from 

 defect in any quality whatever. 



It is undoubtedly true that many of our domesticated races 

 can be proved to have arisen as "sports," and that no great 

 change of type can be effected, by the methods of the breeder, 

 without sports ; but there seem to be both evidence and theoreti- 

 cal ground for holding that, in this particular, artificial selection 

 gives no measure of natural selection. 



It seems to me that, notwithstanding the great value of Gal- 

 ton's data, they fail to prove that the " principle of organic 

 stability" owes its existence to anything except past selection; 

 that regression to mediocrity occurs when ancestry is studied 

 uncomplicated by nurture; that the "mid-parent" is anything else 

 than the actual parent; that "sports" are fundamentally different 

 from the ordinary differences between individuals ; or that natural 

 selection is restricted to the preservation of sports. 



Our tendency to believe that a type is something more real 

 and substantial than the transitory phenomena which exhibit it, is 

 deeply rooted in our minds. 



As the very nature of this belief renders disproof of it impos- 

 sible, we can feel little surprise at its appearance and reappear- 

 ance time after time in the history of thought, although science 

 is based upon the well-warranted opinion that, whether types are 

 real or unreal, we know them only as generalizations or abstrac- 

 tions constructed by our minds out of experience of the orderly 

 sequence of phenomena. 



In zoology and botany the conception of species is unquestion- 

 ably valid and justifiable, and as its most obvious characteristic is 

 its persistency, as contrasted with the fleeting procession of eva- 



