| → that of the 1869 1872 |
| the 1859 1860 1861 1866 |
|
| → perfect birds, some frequently departing 1869 |
| to perfection, and frequently individuals are born which depart 1859 1860 1861 1866 |
| perfect birds, many departing 1872 |
|
| → further variability, 1869 |
| further variability of all kinds, 1859 1860 1861 1866 |
| new variations, 1872 |
|
| → OMIT 1869 1872 |
| there may always be expected to be 1859 1860 1861 1866 |
|
| → modification may always be expected. 1869 1872 |
| modification. 1859 1860 1861 1866 |
|
| → characters, modified through selection by man, are sometimes transmitted, 1869 |
| these variable characters, produced by man's selection, sometimes become attached, 1859 1860 1861 1866 |
|
|
in the carriage and tail of
fantails, &c., these being the points now mainly attended to by English fanciers. Even in
as in
→that of the
short-faced
it is notoriously difficult to breed
nearly
→perfect birds, some frequently departing
widely from the standard. There may
said to be a constant struggle going on between, on the one hand, the tendency to reversion to a less
state, as well as an innate tendency to
→further variability,
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
as to breed
bird as coarse as a common tumbler
a good short-faced strain. But as long as selection is rapidly going on,
→OMIT
much variability in the
undergoing
→modification may always be expected. It further deserves notice that
→characters, modified through selection by man, are sometimes transmitted,
from causes quite unknown to us, more to one sex than to the other, generally to the male sex, as with the wattle of carriers and the enlarged crop of pouters. |
|
| Now let us turn to nature. When a part has been developed in an extraordinary manner in any one species, compared with the other species of the same genus, we may conclude that this part has undergone an extraordinary amount of
since the period when the
branched off from the common progenitor of the genus. This period will seldom be remote in any extreme degree, as species
rarely endure for more than one geological period. An extraordinary amount of modification implies an unusually large and long-continued amount of variability, which has continually been accumulated by natural selection for the benefit of the species. But as the variability of the
part or organ has been so great and long-continued within a period not
remote,
|
