HIGHLY VARIABLE. 143 



habiting the same country, vary extremely little, I have 

 particularly attended to them; and the rule certainly seems 

 to hold good in this class. 1 cannot make out that it 

 applies to plants, and this would have seriously shaken my 

 belief in its truth, had not the great variability in plants 

 made it particularly difficult to compare their relative de- 

 grees of variability. 



When we see any part or organ developed in a remark- 

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

 that it is of high importance to that species: nevertheless 

 it is in this case eminently liable to variation. Why 

 should this be so? On the view tbat 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 ap- 

 plied, 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 either has not or cannot have 

 come into full play, and thus the organization is left in a 

 fluctuating condition. Bat what here more particularly 

 concerns us is, that those points in onr 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 



