HIGHLY VARIABLE 135 



able degree or manner in a species, the fair presumption is 

 that it is of high importance to that species : neverthe- 

 less it is in this case eminently liable to variation. Why 

 should this be so ? On the view that each species has been 

 independently created, with all its parts as we now see 

 them, I can see no explanation. But on the view that 

 groups of species are descended from some other species 

 and have been modified through natural selection, I think 

 we can obtain some light. First let me make some pre- 

 liminary remarks. If, in our domestic animals, any part 

 or the whole animal be neglected, and no selection be 

 applied, that part (for instance, the comb in the Dorking 

 fowl) or the whole breed will cease to have a uniform 

 character ; and the breed may be said to be degenerating. 

 In rudimentary organs, and in those which have been but 

 little specialized for any particular purpose, and perhaps 

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

 in such cases natural selection e' J jher has not or cannot 

 have come into full play, and tb'^ the organization is left 

 in a fluctuating condition. But A r hat here more particularly 

 concerns us is, that those points in our domestic animals, 

 which at the present time are undergoing rapid change by 

 continued selection, are also eminently liable to variation. 

 Look at the individuals of the same breed of the pigeon, 

 and see what a prodigious amount of difference there is in 

 the beaks of tumblers, in the beaks and wattle of carriers, 

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

 points now mainly attended to by English fanciers. Even 

 in the same sub-breed, as in that of the short-faced tumbler, 

 it is notoriously difficult to breed nearly perfect birds, many 

 departing widely from the standard. There may truly be 

 said to be a constant struggle going on between, on the 

 one hand, the tendency to reversion to a less perfect state, 

 as well as an innate tendency to new variations, 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 completely as to breed a bird as 

 Boarse as a common tumbler pigeon from a good short-faced 

 strain. But as long as selection is rapidly going on, much 

 variability in the parts undergoing modification may always 

 be expected. 



Now let us turn to nature. When a part has been de- 

 veloped in an extraordinary manner in any one species, 

 Compared with the other species of the same genus, we may 



