172 ESSAY ON CLASSIFICATION 



derived from one common stock; 2d, that the supposition that these 

 varieties have originated from the complete amalgamation of several 

 primitively distinct species is out of the question; and 3d, that 

 varieties imported from distant countries and not before brought 

 together, such as the Shanghae fowl, for instance, do not completely 

 mingle? Where is the physiologist who can conscientiously affirm 

 that the limits of the fertility between distinct species are ascertained 

 with sufficient accuracy to make it a test of specific identity? And 

 who can say that the distinctive characters of fertile hybrids and of 

 unmixed breeds are sufficiently obvious to enable anybody to point 

 out the primitive features of all our domesticated animals or of all 

 our cultivated plants? As long as this cannot be done, as long as the 

 common origin of all races of men and of the different animals and 

 plants mentioned above is not proved, while their fertility with one 

 another is a fact which has been daily demonstrated for thousands 

 of years; as long as large numbers of animals are hermaphrodites, 

 never requiring a connection with other individuals to multiply 

 their species; as long as there are others which multiply in various 

 ways without sexual intercourse, it is not justifiable to assume that 

 those animals and plants are unmixed species and that sexual fe- 

 cundity is the criterion of specific identity. Moreover, this test can 

 hardly [if] ever have any practical value in most cases of the highest 

 scientific interest. It is never resorted to, and, as far as I know, has 

 never been applied with satisfactory results to settle any doubtful 

 case. It has never assisted any anxious and conscientious naturalist 

 in investigating the degree of relationship between closely allied 

 animals or plants living in distant regions or in disconnected geo- 

 graphical areas. It will never contribute to the solution of any of 

 those difficult cases of seeming difference or identity between ex- 

 tinct animals and plants found in different geological formations. 

 In all critical cases, requiring the most minute accuracy and pre- 

 cision, it is discarded as unsafe and of necessity questionable. Ac- 

 curate science must do without it, and the sooner it is altogether 

 discarded, the better. But like many relics of past time, it is dragged 

 in as a sort of theoretical bugbear and exhibited only now and then 

 to make a false show in discussions upon the question of the unity of 

 origin of mankind. 



There is another fallacy connected with the prevailing ideas about 



