Organic Evolution. 227 



the ancons have been observed to keep together, separating 

 themselves from the rest of the flock when put into 

 enclosures with other sheep. Here, then, we have pre- 

 ferential mating as the further isolating factor. I feel 

 disposed, therefore, to agree with Mr. Galton when he 

 says,* "The theory of natural selection might dispense 

 with a restriction for which it is difficult to see either the 

 need or the justification, namely, that the course of evolu- 

 tion always proceeds by steps that are severally minute, 

 and that become effective only through accumulation. 

 That the steps may be small, and that they must be small, 

 are very different views; it is only to the latter that I 

 object, and only when the indefinite word ' small ' is used 

 in the sense of * barely discernible,* or as small as com- 

 pared with such large sports as are known to have been 

 the origins of new races." 



Connected, perhaps, with the phenomena we have just 

 been considering is that of prepotency. '\ It is found that, 

 when two individuals of the same race or of different races 

 are crossed, one has a preponderant influence in deter- 

 mining the character of the offspring. Thus the famous 

 bull Favourite is believed to have had a prepotent influence 

 on the short-horn race; and the improved short-horns 

 possess great power in impressing their likeness on other 

 breeds. The phenomena are in some respects curiously 

 variable. In fowls, silkiness of feathers seems to be at 

 once bred out by intercrossing between silk-fowl and any 

 other breed. But in the silky variety of the fan-tail 

 pigeon this character seems prepotent; for, when the 

 variety is crossed with any other small-sized race, the 

 silkiness is invariably transmitted. One may fairly sup- 

 pose that prepotent characters have unusual stability; 

 but to what causes this stabihty is due we are at present 

 ignorant. 



Lastly, we have to consider the phenomenon of latency. 



* " Natural Inheritance," p. 32. 



t See " Animals and Plants under Domestication." vol. ii. p. 40, from 

 wlucb illustrations are taken. 



