CHAPTER VIII - INSTINCT
MANY instincts are so wonderful that their development will probably
appear to the reader a difficulty sufficient to overthrow my whole
theory. I may here premise that I have nothing to do with the origin
of the mental powers, any more than I have with that of life itself.
We are concerned only with the diversities of instinct and of the
other mental faculties in animals of the same class.
I will not attempt any definition of instinct. It would be easy to
show that several distinct mental actions are commonly embraced by
this term; but every one understands what is meant, when it is said
that instinct impels the cuckoo to migrate and to lay her eggs in
other birds' nests. An action, which we ourselves require experience
to enable us to perform, when performed by an animal, more
especially by a very young one, without experience, and when performed
by many individuals in the same way, without their knowing for what
purpose it is performed, is usually said to be instinctive. But I
could show that none of these characters are universal. A little
dose of judgment or reason, as Pierre Huber expresses it, often
comes into play, even with animals low in the scale of nature.
Frederic Cuvier and several of the older metaphysicians have
compared instinct with habit. This comparison gives, I think, an
accurate notion of the frame of mind under which an instinctive action
is performed, but not necessarily of its origin. How unconsciously
many habitual actions are performed, indeed not rarely in direct
opposition to our conscious will! Yet they may be modified by the will
or reason. Habits easily become associated with other habits, with
certain periods of time, and states of the body. When once acquired,
they often remain constant throughout life. Several other points of
resemblance between instincts and habits could be pointed out. As in
repeating a well-known song, so in instincts, one action follows
another by a sort of rhythm; if a person be interrupted in a song,
or in repeating anything by rote, he is generally forced to go back to
recover the habitual train of thought; so P. Huber found it was with a
caterpillar, which makes a very complicated hammock; for if he took
a caterpillar which had completed its hammock up to, say, the sixth
stage of construction, and put it into a hammock completed up only
to the third stage, the caterpillar simply reperformed the fourth,
fifth, and sixth stages of construction. if, however, a caterpillar
were taken out of a hammock made up, for instance, to the third stage,
and were put into one finished up to the sixth stage, so that much
of its work was already done for it, far from deriving any benefit
from this, it was much embarrassed, and in order to complete its
hammock, seemed forced to start from the third stage, where it had
left off, and thus tried to complete the already finished work.
If we suppose any habitual action to become inherited - and it can be
shown that this does sometimes happen - then the resemblance between
what originally was a habit and an instinct becomes so close as not to
be distinguished. If Mozart, instead of playing the pianoforte at
three years old with wonderfully little practice, had played a tune
with no practice at all, he might truly be said to have done so
instinctively. But it would be a serious error to suppose that the
greater number of instincts have been acquired by habit in one
generation, and then transmitted by inheritance to succeeding
generations. It can be clearly shown that the most wonderful instincts
with which we are acquainted, namely, those of the hive-bee and of
many ants, could not possibly have been acquired by habit.
It will be universally admitted that instincts are as important as
corporeal structures for the welfare of each species, under its
present conditions of life. Under changed conditions of life, it is at
least possible that slight modifications of instinct might be
profitable to a species; and if it can be shown that instincts do vary
ever so little, then I can see no difficulty in natural selection
preserving and continually accumulating variations of instinct to
any extent that was profitable. It is thus, as I believe, that all the
most complex and wonderful instincts have originated. As modifications
of corporeal structure arise from, and are increased by, use or habit,
and are diminished or lost by disuse, so I do not doubt it has been
with instincts. But I believe that the effects of habit are in many
cases of subordinate importance to the effects of the natural
selection of what may be called spontaneous variations of
instincts;- that is of variations produced by the same unknown
causes which produce slight deviations of bodily structure.
No complex instinct can possibly be produced through natural
selection, except by the slow and gradual accumulation of numerous
slight, yet profitable, variations. Hence, as in the case of corporeal
structures, we ought to find in nature, not the actual transitional
gradations by which each complex instinct has been acquired- for these
could be found only in the lineal ancestors of each species- but we
ought to find in the collateral lines of descent some evidence of such
gradations; or we ought at least to be able to show that gradations of
some kind are possible; and this we certainly can do. I have been
surprised to find, making allowance for the instincts of animals
having been but little observed except in Europe and North America,
and for no instinct being known amongst extinct species, how very
generally gradations, leading to the most complex instincts, can be
discovered. Changes of instinct may sometimes be facilitated by the
same species having different instincts at different periods of
life, or at different seasons of the year, or when placed under
different circumstances, &c; in which case either the one or the other
instinct might be preserved by natural selection. And such instances
of diversity of instinct in the same species can be shown to occur
in nature.
Again, as in the case of corporeal structure, and conformably to
my theory, the instinct of each species is good for itself, but has
never, as far as we can judge, been produced for the exclusive good of
others. One of the strongest instances of an animal apparently
performing an action for the sole good of another, with which I am
acquainted, is that of aphides voluntarily yielding, as was first
observed by Huber, their sweet excretion to ants: that they do so
voluntarily, the following facts show. I removed all the ants from a
group of about a dozen aphides on a dock-plant, and prevented their
attendance during several hours. After this interval, I felt sure that
the aphides would want to excrete. I watched them for some time
through a lens, but not one excreted; I then tickled and stroked
them with a hair in the same manner, as well as I could, as the ants
do with their antennae; but not one excreted. Afterwards I allowed
an ant to visit them, and it immediately seemed, by its eager way of
running about, to be well aware what a rich flock it had discovered;
it then began to play with its antennae on the abdomen first of one
aphis and then of another; and each, as soon as it felt the
antennae, immediately lifted up its abdomen and excreted a limpid drop
of sweet juice, which was eagerly devoured by the ant. Even the
quite young aphides behaved in this manner, showing that the action
was instinctive, and not the result of experience. It is certain, from
the observations of Huber, that the aphides show no dislike to the
ants: if the latter be not present they are at last compelled to eject
their excretion. But as the excretion is extremely viscid, it is no
doubt a convenience to the aphides to have it removed; therefore
probably they do not excrete solely for the good of the ants. Although
there is no evidence that any animal performs an action for the
exclusive good of another species, yet each tries to take advantage of
the instincts of others, as each takes advantage of the weaker
bodily structure of other species. So again instincts cannot be
considered as absolutely perfect; but as details on this and other
such points are not indispensable, they may be here passed over.
As some degree of variation in instincts under a state of nature,
and the inheritance of such variations, are indispensable for the
action of natural selection, as many instances as possible ought to be
given; but want of space prevents me. I can only assert that instincts
certainly do vary- for instance, the migratory instinct, both in
extent and direction, and in its total loss. So it is with the nests
of birds, which vary partly in dependence on the situations chosen,
and on the nature and temperature of the country inhabited, but
often from causes wholly unknown to us: Audubon has given several
remarkable cases of differences in the nests of the same species in
the northern and southern United States. Why, it has been asked, if
instinct be variable, has it not granted to the bee "the ability to
use some other material when wax was deficient"? But what other
natural material could bees use? They will work, as I have seen,
with wax hardened with vermilion or softened with lard. Andrew
Knight observed that his bees, instead of laboriously collecting
propolis, used a cement of wax and turpentine, with which he had
covered decorticated trees. It has lately been shown that bees,
instead of searching for pollen, will gladly use a very different
substance, namely oatmeal. Fear of any particular enemy is certainly
an instinctive quality, as may be seen in nestling birds, though it is
strengthened by experience, and by the sight of fear of the same enemy
in other animals. The fear of man is slowly acquired, as I have
elsewhere shown, by the various animals which inhabit desert
islands; and we see an instance of this even in England, in the
greater wildness of all our large birds in comparison with our small
birds; for the large birds have been most persecuted by man. We may
safely attribute the greater wildness of our large birds to this
cause; for in uninhabited islands large birds are not more fearful
than small; and the magpie, so wary in England, is tame in Norway,
as is the hooded crow in Egypt.
That the mental qualities of animals of the same kind, born in a
state of nature, vary much, could be shown by many facts. Several
cases could also be adduced of occasional and strange habits in wild
animals, which, if advantageous to the species, might have given rise,
through natural selection, to new instincts. But I am well aware
that these general statements, without the facts in detail, will
produce but a feeble effect on the reader's mind. I can only repeat my
assurance, that I do not speak without good evidence.
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