| → of structure often appears, 1860 1861 1866 1869 1872 |
| appears not unfrequently, 1859 |
|
| → for the most part unknown. No 1869 1872 |
| quite unknown; no 1859 1860 1861 1866 |
|
|
doubts how strong is the tendency to
produces like is his fundamental belief: doubts have been thrown on this principle
theoretical
When
deviation
→of structure often appears,
and we see it in the father and child, we cannot tell whether it may not be due to the same
cause
on both; but when amongst individuals, apparently exposed to the same conditions, any very rare deviation, due to some extraordinary combination of circumstances, appears in the parent — say, once
several million individuals — and it reappears in the child, the mere doctrine of chances almost compels us to attribute its reappearance to inheritance. Every one must have heard of cases of albinism, prickly skin, hairy bodies, &c., appearing in several members of the same family. If strange and rare deviations of structure are
inherited, less strange and commoner deviations may be freely admitted to be inheritable. Perhaps the correct way of viewing the whole
would be, to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly. |
|
| The laws governing inheritance are
→for the most part unknown. No
one can say why
peculiarity in different individuals of the same species,
in
different species, is sometimes inherited and sometimes not so; why the child often reverts in certain
to its
or grandmother or
more remote ancestor; why a peculiarity is often transmitted from one sex to both sexes, or to one sex alone, more commonly but not exclusively to the like sex. It is a fact of some
importance to us, that peculiarities appearing in the males of our domestic breeds are often
either
or in a much greater degree, to
alone. A much more important rule, which I think may be trusted, is that, at whatever period of life a peculiarity first appears, it tends to
in the offspring at a corresponding age, though sometimes earlier. In many cases this could not be
thus the inherited peculiarities in the horns of cattle could appear only in the offspring when nearly mature; peculiarities in the
are known to appear at the corresponding caterpillar or cocoon stage. But hereditary diseases and some other facts make me believe that the rule has a wider extension, and
when there is no apparent reason why a peculiarity should appear at any particular age, yet that it does tend to appear in the offspring at the same period at which it first appeared in the parent. I believe this rule to be of the highest importance in explaining the laws of embryology. These remarks are of course confined to the first
appearance
of the peculiarity, and not to
primary
|
