152 
LAWS OF YAETATIOK. 
Chap. Y. 
presumption is that it is of high importance to that 
species; nevertheless the part in this case is 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 
have descended from other species, and have been mo¬ 
dified 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 selection be ap¬ 
plied, 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 condi¬ 
tion. 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 eminently liable to variation. Look 
at the breeds of the pigeon; see what a prodigious 
amount of difference there is in the beak of the differ¬ 
ent tumblers, in the beak and wattle of the different 
carriers, in the carriage and tail of our fantails, &c., 
these being the points now mainly attended to by Eng¬ 
lish 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 
