CHAPTER I. VARIATION UNDER DOMESTICATION.
2. EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS; CORRELATED VARIATION; INHERITANCE. (continued)
The results of the various, unknown, or but dimly understood laws of
variation are infinitely complex and diversified. It is well worth while
carefully to study the several treatises on some of our old cultivated
plants, as on the hyacinth, potato, even the dahlia, etc.; and it is really
surprising to note the endless points of structure and constitution in
which the varieties and sub-varieties differ slightly from each other. The
whole organisation seems to have become plastic, and departs in a slight
degree from that of the parental type.
Any variation which is not inherited is unimportant for us. But the number
and diversity of inheritable deviations of structure, both those of slight
and those of considerable physiological importance, are endless. Dr.
Prosper Lucas' treatise, in two large volumes, is the fullest and the best
on this subject. No breeder doubts how strong is the tendency to
inheritance; that like produces like is his fundamental belief: doubts
have been thrown on this principle only by theoretical writers. When any
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 having
acted on both; but when among individuals, apparently exposed to the same
conditions, any very rare deviation, due to some extraordinary combination
of circumstances, appears in the parent--say, once among 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, etc.,
appearing in several members of the same family. If strange and rare
deviations of structure are truly inherited, less strange and commoner
deviations may be freely admitted to be inheritable. Perhaps the correct
way of viewing the whole subject would be, to look at the inheritance of
every character whatever as the rule, and non-inheritance as the anomaly.