43-4: CONCLUDING EEMAEKS. Chap. XXVIII. 



intentional selection; more frequently, it is probable, by un- 

 conscious selection, and partly by natural selection, for animals 

 kept in semi-civilised countries have to provide largely for their 

 own wants. Such natural breeds will also, it may be presumed 

 have been directly acted on to some extent by the differences 



though slight, in the surrounding physical 



It is a much more important distinction that some breeds Lave 

 been from their first origin modified in so slow and insensible a 

 manner, that if we could see their early progenitors we should 

 hardly be able to say when or how the breed first arose ; whilst 

 other breeds have originated from a strongly-marked or semi- 

 monstrous deviation of structure, which, however, may subse- 

 quently have been augmented by selection. From what we 

 know of the history of the racehorse, greyhound, gamecock, 

 &c, and from their general appearance, we may feel nearly con- 

 fident that they were formed by a slow process of improvement : 

 and with the carrier-pigeon, as well as with some other pigeons, 

 we know that this has been the case. On the other hand, it is 

 certain that the ancon and mauchamp breeds of sheep, and 

 almost certain that the niata cattle, turnspit and pug-dogs, 

 jumper and frizzled fowls, short-faced tumbler pigeons, hook- 

 billed ducks, &c, and with plants a multitude of varieties, sud- 

 denly appeared in nearly the same state as we now see them. 

 The frequency of these cases is likely to lead to the false 

 belief that natural species have often originated in the same 

 abrupt manner. But we have no evidence of the appearance, or 

 at least of the continued procreation, under nature, of abrupt 

 modifications of structure ; and various general reasons could be 

 assigned against such a belief: for instance, without separation 

 a single monstrous variation would almost certainly be soon 

 obliterated by crossing. 



On the other hand, we have abundant evidence of the con- 

 stant occurrence under nature of slight individual differences of 

 the most diversified kinds ; and thus we are led to conclude that 

 species have generally originated by the natural selection, not of 

 abrupt modifications, but of extremely slight differences. This 

 process may be strictly compared with the slow and gradual im- 

 provement of the racehorse, greyhound, and gamecock. As every 

 detail of structure in each species is closely adapted to its general 



