300 GENERAL BIOLOGY 



sciously or unconsciously we arrange the individuals 

 of a group by the common possession or lack of 

 possession of certain visible characters. Such a 

 method of discriminating species has been called the 

 diagnostic method. It is obvious that the individual 

 judgment must play a large part in deciding the im- 

 portance or constancy of such characters. A species 

 judged by such a method cannot have any wholly 

 accurate definition, so long as the personal equation 

 enters so largely. 1 



When we trace resemblances between human 

 beings, we usually adopt a similar method, that is, 

 we catalogue their physical characters and group 

 the individuals by their common possession of such 

 characters. Thus, in spite of individual peculiarities, 

 we have no difficulty in distinguishing a Swede 

 from an Italian, nor a Chinese from both. The 

 first two resemble one another, in spite of their 

 differences, more than they resemble the Oriental. 

 In the same way, a child frequently resembles iis 

 immediate parents, more rarely a grandparent, and 

 much more rarely a cousin, an uncle, or a more 

 remote relative. We accept it as a matter of course 



1 In the middle of the eighteenth century Buffon proposed a criterion 

 of species that avoided this difficulty. He held fertility in crossing to 

 be the test of specific identity. If two forms were sterile when inter- 

 bred, they were distinct species ; if not, they were varieties of one species 

 provided the hybrids themselves were not sterile. This essentially 

 scientific hypothesis, which for clearness and workableness has much to 

 commend it, had the curious result of emphasizing the concept of Special 

 Creation, since if it were uniformly true, it is hard to see how new species 

 could ever arise. 



