138 ON THE ORIGIN OF SPECIES 



modified through natural selection, I think we can 

 obtain some light. In our domestic animals, if any 

 part, or the whole animal, be neglected and no selec- 

 tion be applied, that part (for instance, the comb in 

 the Dorking fowl) or the whole breed will cease to have 

 a nearly uniform character. The breed will then be 

 said to have degenerated. In rudimentary organs, 

 and in those which have been but little specialised for 

 any particular purpose, and perhaps in polymorphic 

 groups, we see a nearly parallel natural case ; for in 

 such cases natural selection either has not or cannot 

 come into full play, and thus the organisation is left 

 in a fluctuating condition. But what here more 

 especially concerns us is, that in our domestic animals 

 those points, which at the present time are undergoing 

 rapid change by continued selection, are also emi- 

 nently liable to variation. Look at the breeds of the 

 pigeon ; see what a prodigious amount of difference 

 there is in the beak of the different tumblers, in the 

 beak and wattle of the different carriers, in the 

 carriage and tail of our fantails, etc., these being the 

 points now mainly attended to by English fanciers. 

 Even in the sub-breeds, as in the short-faced tumbler, 

 it is notoriously difficult to breed them nearly to 

 perfection, and frequently individuals are born which 

 depart widely from the standard. There may be truly 

 said to be a constant struggle going on between, on 

 the one hand, the tendency to reversion to a less 

 modified state, as well as an innate tendency to further 

 variability of all kinds, and, on the other hand, the 

 power of steady selection to keep the breed true. In 

 the long run selection gains the day, and we do not 

 expect to fail so far as to breed a bird as coarse as a 

 common tumbler from a good short-faced strain. But 

 as long as selection is rapidly going on, there may 

 always be expected to be much variability in the struc- 

 ture undergoing modification. It further deserves 

 notice that these variable characters, produced by 

 man's selection, sometimes become attached, from 

 causes quite unknown to us, more to one sex than to 



