THE GROWTH OF GROUPS 45 



We may examine the mass either by taking a few 

 individuals from many widely separate places or by 

 examining a large number of them at a few places ; but, 

 however we proceed, we shall find that its component 

 members are not all alike. They present certain 

 differences. These differences are not " in all directions," 

 supposing for the moment that we can imagine things 

 chaotic. On the contrary, they are in certain directions, 

 the same kind of difference being found again and again 

 in various places. 



We will now discuss and enumerate the differences. 

 They are of colour for the most part. This is because 

 such differences are easily appreciated by our senses. 

 We cannot say with confidence of any two rats " the 

 one is brown and the other black, and this is the only 

 difference between them." The one may be fertile, 

 pugnacious, and healthy ; the other sterile, timid, and 

 susceptible to certain diseases. We choose characteristics 

 of colour for discussion because they happen to be obvious 

 to our senses, but such characters are merely a few 

 chosen from among a large and unknown number. We 

 cannot measure the importance of characters by their 

 degree of visibility. Even if we confine our attention 

 to colour, the same point of view should be taken. An 

 observer may say of three rats, " This one is black, but 

 those two are alike, they are both brown." But a second 

 observer may say of the same three animals, " To be sure, 

 the black one is quite different from the others, but the 

 brown ones are not alike, there is a reddish tint in the fur 

 of one which is absent in the other ; moreover it is possible 

 to see the same characteristic both in the parents and 

 offspring of that individual." The contention of the 



