THE GROWTH OF GROUPS 63 



arose. But we know of certain events which will help 

 us to form an opinion. It is known that a pair of normally 

 coloured panthers may produce normal offspring and 

 black offspring in the same litter. The black sheep in 

 every fold is proverbial. Many other animals are known 

 to produce black offspring in this sudden manner, and 

 it is also well known that such sports when mated together 

 produce offspring of their own kind. 



My argument is this. Black animals arise in some 

 way from brown animals. The method of their origin 

 has been observed in certain cases. Whenever it has 

 been observed, the whole difference between brown and 

 black has appeared in a single step. The parent has been 

 brown, the offspring has been black. Hence we actually 

 know that black animals take origin suddenly. Why, 

 then, is it necessary to believe that black animals usually 

 take origin by another method? It is unwise to look 

 at the same kind of event on many occasions, to perceive 

 that the method of it is the same on each occasion, and yet 

 to believe that the method observed does not indicate 

 the true method. Why should we think that visible 

 events are exceptional and unreal and prefer to believe 

 in the reality of some process which has never been 

 seen ? 



I imagine that the history of the group was as follows. 

 A large black mole-rat was born of grey-brown parents 

 of normal size. Even though it mated with one of the 

 common kind we know, from Mendel's discovery, that 

 some of its grand-offspring would resemble their grand- 

 parent in body and in germ. These, ty inbreeding, 

 founded the colony. Such a colony could not become 

 established unless it were isolated by some means, either 



