Darwin holds that in some cases selection alone has modified the
instincts and dispositions of domesticated animals, but that in most
cases selection and the inheritance of acquired habits have concurred in
effecting the change. "On the other hand," he says, "habit alone in some
cases has sufficed; hardly any animal is more difficult to tame than the
young of the wild rabbit; scarcely any animal is tamer than the young of
the tame rabbit; but I can hardly suppose that domestic rabbits have
often been selected for tameness alone; so that we must attribute at
least the greater part of the inherited change from extreme wildness to
extreme tameness to habit and long-continued close confinement."[42]
But there are strong, and to me irresistible, arguments to the contrary.
I think that the following considerations will show that the greater
part, if not the whole, of the change must be attributed to selection
rather than to the direct inheritance of acquired habit.
(1) For a period which may cover thousands of generations, there has
been an entire cessation of the natural selection which maintains the
wildness (or excessive fear, caution, activity, &c.) so indispensably
essential for preserving defenceless wild rabbits of all ages from the
many enemies that prey upon them.
(2) During this same extensive period of time man has usually killed off
the wildest and bred from the tamest and most manageable. To some extent
he has done this consciously. "It is very conducive to successful
breeding to keep only such as are quiet and tractable," says an
authority on rabbits,[43] and he enjoins the selection of the
handsomest and _best-tempered_ does to serve as breeders. To a still
greater extent man has favoured tameness unconsciously and indirectly.
He has systematically selected the largest and most prolific animals,
and has thus doubled the size and the fertility of the domestic rabbit.
In consciously selecting the largest and most flourishing individuals
and the best and most prolific mothers, he _must_ have unconsciously
selected those rabbits whose relative _tameness_ or placidity of
disposition rendered it possible for them to flourish and to produce and
rear large and thriving families, instead of fretting and pining as the
wilder captives would do. When we consider how exceedingly delicate and
easily disturbed yet all-important a function is that of maternity in
the continually breeding rabbit, we see that the tamest and the least
terrified would be the most successful mothers, and so would continually
be selected, although man cared nothing for the tameness in itself. The
tamest mothers would also be less liable to neglect or devour their
offspring, as rabbits commonly do when their young are handled too soon,
or even when merely frightened by mice, &c., or disturbed by changed
surroundings.
(3) We must remember the extraordinary fecundity of the rabbit and the
excessive amount of elimination that consequently takes place either
naturally or artificially. Where nature preserved only the wildest, man
has preserved the tamest. If there is any truth in the Darwinian theory,
this thorough and long-continued reversal of the selective process
_must_ have had a powerful effect. Why should it not be amply sufficient
to account for the tameness and mental degeneracy of the rabbit without
the aid of a factor which can readily be shown to be far weaker in its
normal action than either natural or artificial selection? Why may not
the tameness of the rabbit be transferred to the group of cases in
which Darwin holds that "habit has done nothing," and selection has done
all?
(4) If use-inheritance has tamed the rabbit, why are the bucks still so
mischievous and unruly? Why is the Angora breed the only one in which
the males show no desire to destroy the young? Why, too, should
use-inheritance be so much more powerful in the rabbit than with other
animals which are far more easily tamed in the first instance? Wild
young rabbits when domesticated "remain unconquerably wild," and,
although they may be kept alive, they pine and "rarely come to any
good." Yet the animal which _acquires_ least tameness--or apparently,
indeed, none at all--inherits most! It appears, in fact, to inherit that
which it cannot acquire--a circumstance which indicates the selection of
spontaneous variations rather than the inheritance of changed habits.
Such variations occasionally occur in animals in a marked degree. Of a
litter of wolf-cubs, all brought up in the same way, "one became tame
and gentle like a dog, while the others preserved their natural
savagery." Is it not probable that permanent domestication was rendered
possible by the inevitable selection of spontaneous variations in this
direction? The _excessive_ tameness, too, of the young rabbit, while
easily explicable as a result of unconscious selection, is not easily
explained as a result of acquired habit. No particular care is taken to
tame or teach or domesticate rabbits. They are bred for food, or for
profit or appearance, and they are left to themselves most of their
time. As Sir J. Sebright notices with some surprise, the domestic rabbit
"is not often visited, and seldom handled, and yet it is always tame."