128 EVOLUTION [Chap. Ill 



Letter So of the crossing and blending of the aboriginal stocks. You 

 will sec this briefly put in the first chapter. Generally, with 

 respect to crossing, the effects may be diametrically opposite. 

 If you cross two very distinct races, you may make (not that 

 I believe such has often been madc_) a third and new inter- 

 mediate race ; but if you cross two exceedingly close races, 

 or two slightly different individuals of the same race, then in 

 fact you annul and obliterate the difference. In this latter 

 way I believe crossing is all-important, and now for twenty 

 years I have been working at flowers and insects under this 

 point of view. I do not like Hooker's terms, centripetal 

 and centrifugal ' : they remind me of Forbes' bad term of 

 Polarity. 2 



I daresay selection by man would generally work quicker 

 than Natural Selection ; but the important distinction between 

 them is, that man can scarcely select except external and 

 visible characters, and secondly, he selects for his own good ; 

 whereas under nature, characters of all kinds are selected 

 exclusively for each creature's own good, and arc well 

 exercised ; but you will find all this in Chapter IV. 



Although the hound, greyhound, and bull-dog may possi- 

 bly have descended from three distinct stocks, I am convinced 

 that their present great amount of difference is mainly due 

 to the same causes which have made the breeds of pigeons 

 so different from each other, though these breeds of pigeons 

 have all descended from one wild stock ; so that the Pallasian 

 doctrine I look at as but of quite secondary importance. 



In my bigger book I have explained my meaning fully; 

 whether I have in the Abstract I cannot remember. 



that the hybrids subsequently reared under domestication became quite 

 fertile. This latter alternative, which was first propounded by Pallas, 

 seems by far the most probable, and can, indeed, hardly be doubted " 

 {Origin of Species, Ed. VI., p. 240). 



1 Hooker's Introductory Essay to the Flora of Tasmania, pp. viii 

 and ix. 



- Forbes, "On the Manifestation of Polarity in the Distribution of 

 Organised Beings in Time." R. Institution Proc, I., 1851-54. 



