Conscious concomitant.
It is in the first place desirable to distinguish between the word
"instinct" (Lat. _instinctus_, from _instinguere_, to incite, impel) as
employed in general literature and the term "instinct" as used in
scientific discourse. The significance of the former is somewhat
elastic, and is in large measure determined by the context. Thus in
social relationships we speak of "instinctive" liking or distrust; we
are told that the Greeks had "instinctive" appreciation of art; we hear
of an instinct of reverence or "instinctive" beliefs. We understand what
is meant and neither desire nor demand a strict definition. But in any
scientific discussion the term instinct must be used within narrower
limits, and hence it is necessary that the term should be defined. There
are difficulties, however, in framing a satisfactory definition. That
given by G. J. Romanes in the 9th edition of the _Encyclopaedia
Britannica_ runs as follows: "Instinct is a generic term comprising all
those faculties of mind which lead to the conscious performance of
actions that are adaptive in character but pursued without necessary
knowledge of the relation between the means employed and the ends
attained." This has been criticized both from the biological and from
the psychological standpoint. From the biological point of view the
reference of certain modes of behaviour, termed instinctive, to
faculties of mind for which "instinct" is the generic term is scarcely
satisfactory; from the psychological point of view the phrase "without
necessary knowledge of the relation between the means employed and the
end attained" is ambiguous. (See INTELLIGENCE OF ANIMALS.) In recent
scientific literature the term is more frequently used in its adjectival
than in its substantive form; and the term "instinctive" is generally
applied to certain hereditary modes of behaviour. Investigation thus
becomes more objective, and this is a distinct advantage from the
biological point of view. It is indeed sometimes urged that instinctive
modes of behaviour should be so defined as to entirely exclude any
reference to their psychological concomitants in consciousness, which
are, it is said, entirely inferential. But as a matter of fact no small
part of the interest and value of investigations in this field of
inquiry lies in the relationships which may thereby be established
between biological and psychological interpretations. Fully realizing,
therefore, the difficulty of finding and applying a criterion of the
presence or absence of consciousness, it is none the less desirable, in
the interests of psychology, to state that truly instinctive acts (as
defined) are accompanied by consciousness. This marks them off from such
reflex acts as are unconsciously performed, and from the tropisms of
plants and other lowly organisms. There remains, however, the difficulty
of finding any satisfactory criterion of the presence of consciousness.
We seem forced to accept a practical criterion for purposes of
interpretation rather than one which can be theoretically defended
against all adverse criticism. We have reason to believe that some
organisms profit by experience and show that they do so by the
modification of their behaviour in accordance with circumstances. Such
modification is said to be individually acquired. To profit by
individual experience is thus the only criterion we possess of the
existence of the conscious experience itself. But if hereditary
behaviour is unaccompanied by consciousness, it can in no wise
contribute to experience, and can afford no data by which the organism
can profit. Hence, for purposes of psychological interpretation it seems
necessary to assume that instinctive behaviour, including the
stimulation by which it is initiated and conditioned, affords that naive
awareness which forms an integral part of what may be termed the
primordial tissue of experience.
We are now in a position to give an expanded definition of instinctive
behaviour as comprising those complex groups of co-ordinated acts which,
though they contribute to experience, are, on their first occurrence,
not determined by individual experience; which are adaptive and tend to
the well-being of the individual and the preservation of the race; which
are due to the co-operation of external and internal stimuli; which are
similarly performed by all members of the same more or less restricted
group of animals; but which are subject to variation, and to subsequent
modification under the guidance of individual experience.
Definitions.
If a brief definition of instinct, from the purely biological point of
view be required, that given in the _Dictionary of Philosophy and
Psychology_ may be accepted: "An inherited reaction of the sensori-motor
type, relatively complex and markedly adaptive in character, and common
to a group of individuals." Instinctive behaviour thus depends solely on
how the nervous system has been built through heredity; while
intelligent behaviour depends also on those characters of the nervous
system which have been acquired under the modifying influence of
individual relation to the environment.
Such definitions, however, are not universally accepted. Wasmann, for
example, divides instinctive actions under two groups: (1) those which
immediately spring from the inherited dispositions; (2) those which
indeed proceed from the same inherited dispositions but through the
medium of sense experience. The first group, which he regards as
instinctive in the strict acceptance of the term, seem exactly to
correspond to those which fall under the definition given above. The
second group, which he regards as instinctive in the wider acceptance of
the term, nearly, if not quite, correspond to those above spoken of as
intelligent--though he regards this term as falsely applied (see
INTELLIGENCE OF ANIMALS). By using the term instinctive in both its
strict and its wider significance, Wasmann includes under it the whole
range of animal behaviour.
Examples from bird life.
It will be seen that from the biological standpoint there fall under the
stricter definition those hereditary modes of behaviour which are
analogous to hereditary forms of structure; and that a sharp line of
distinction is drawn between the behaviour which is thus rendered
definite through heredity, and the behaviour the distinguishing
characteristics of which are acquired in the course of individual life.
What in popular usage are spoken of as the instincts of animals, for
example, the hunting of prey by foxes and wolves, or the procedure of
ants in their nests, are generally joint products of hereditary and
acquired factors. Wasmann's comprehensive definition so far accords with
popular usage. But it tends to minimize the importance of the
distinction of that which is prior to individual experience and that
which results therefrom. It is the business of scientific interpretation
to disentangle the factors which contribute to the joint-products. It is
indeed by no means easy to distinguish between what is dependent on
individual experience, and what is not. Only the careful observation of
organisms throughout the earlier phases of their life-history can the
closely related factors be distinguished with any approach to scientific
accuracy. By the patient study of the behaviour of precocious young
birds, such as chicks, pheasants, ducklings and moorhens, it can be
readily ascertained that such modes of activity as running, swimming,
diving, preening the down, scratching the ground, pecking at small
objects, with the characteristic attitudes expressive of fear and anger,
are so far instinctive as to be definite on their first occurrence--they
do not require to be learnt. No doubt they are subsequently guided to
higher excellence and effectiveness with the experience gained in their
oft-repeated performance. Indeed it may be said that only on the
occasion of their initial performance are they purely instinctive; all
subsequent performance being in some degree modified by the experience
afforded, by previous behaviour of like nature and the results it
affords. It should be remembered that such comparatively simple
activities, though there is little about them to arrest popular
attention, are just the raw material out of which the normal active life
of such organisms is elaborated, and that for scientific treatment they
are therefore not less important than those more conspicuous
performances which seem at first sight to call for special treatment, or
even to demand a supplementary explanation. The instincts of
nest-building, incubation and the rearing of young, though they occur
later in life than those concerned in locomotion and the obtaining of
food, are none the less founded on a hereditary basis, and in some
respects are less rather than more liable to modification by the
experience gained by the carrying out of hereditarily definite modes of
procedure. Here the instinctive factor probably predominates over that
which is experiential. But in the "homing" of pigeons there is little
question that the experiential factor predominates. The habit results
mainly from the modification of the higher nerve-centres through
individual and intelligent use. In the migration of birds we are still
uncertain as to the exact nature and proportional value of the
instinctive and intelligent factors. The impulse to migrate, that is to
say, the calling forth of specific activities by climatal or other
presentations, appears to be instinctive; whether the direction of
migration is in like manner instinctive is a matter of uncertainty; and,
if it be instinctive, the nature of the stimuli and the manner in which
they are hereditarily linked with responsive acts is unexplained. To say
that it is due to hereditary experience is generally regarded as
inadmissible. For modern interpretation hereditary modes of behaviour
afford experience; in no other sense can it be said that experience is
inherited.
Examples from insect life.
A good example of the methods of recent investigation is to be found in
Dr G. W. and Mrs Peckham's minute observations on the habits and
instincts of the solitary wasps. They enumerate the following primary
types of instinctive behaviour: the manner of attacking and capturing a
particular kind of prey which alone affords the requisite presentation
to sense; the manner of conveying the prey to the nest; the general
style and locality of the nest; the method and order of procedure in
stocking the nest with food for the unseen young. It is noteworthy,
however, that although the manner in which the prey is stung (for
example) is on the whole similar in the case of the members of any given
species--that is to say, all the wasps of the species behave in very
much the same manner--yet there are minor variations in detail. This
outcome of prolonged and careful observation is of importance. It
affords a point of departure for the interpretation of the genesis of
existing instincts. Furthermore, the observations on American wasps
render it probable that the earlier accounts of the instinctive
behaviour of such wasps are exaggerated. Romanes thought that the manner
of stinging and paralysing their prey might be justly deemed the most
remarkable instinct in the world. Spiders, caterpillars and grasshoppers
are, he said, stung in their chief nerve-centres, in consequence of
which the victims are not killed outright, but rendered motionless and
continue to live in this paralysed condition for several weeks, being
thus available as food for the larvae when these are hatched. Of course,
he adds, the extraordinary fact which stands to be explained is that of
the precise anatomical, not to say the physiological, knowledge which
appears to be displayed by the insect in stinging only the nerve-centres
of its prey. But the Peckhams' careful observations and experiments show
that, with the American wasps, the victims stored in the nests are quite
as often dead as alive; that those which are only paralysed live for a
varying number of days, some more, some less; that wasp larvae thrive
just as well on dead victims, sometimes dried up, sometimes undergoing
decomposition, as on living and paralysed prey; that the nerve-centres
are not stung with the supposed uniformity; and that in some cases
paralysis, in others death, follows when the victims are stung in parts
far removed from any nerve-centre. It would seem then that by the
stinging of insects or spiders their powers of resistance are overcome
and their escape prevented; that some are killed outright and some
paralysed is merely an incidental result.
Mode of origin.
Granted that instinctive modes of behaviour are hereditary and definite
within the limits of congenital variation, the question of their manner
of genesis is narrowed to a clear issue. Do they originate through the
natural selection of those variations which are the more adaptive; or do
they originate through the inheritance of those acquired modifications
which are impressed on the nervous system in the course of individual
and intelligent use? Romanes, taking up the inquiry where Darwin left
it, came to the conclusion that some instinctive modes of behaviour
which he termed "primary" are due to the operation of natural selection
alone; that others, which he termed "secondary," and of which he could
give few examples, were due to the inheritance of acquired modifications
from which, in the phrase of G. H. Lewes, the intelligence had lapsed;
while others, which he termed "blended," were partly due to natural
selection and partly resulted from the inheritance of acquired habit.
There has been a prolonged controversy between the school of
interpretation, commonly spoken of as Lamarckian, which advocates a
belief in the inheritance of acquired characters, and the school, with
Weismann as their leader, which questions the evidence for, or the
probability of, such inheritance. The trend of modern opinion appears to
be in the direction of the Weismannian interpretation. And it must be
regarded as questionable, if not improbable, that instinctive modes of
behaviour are in any degree directly due to the inheritance of habits
intelligently acquired. That intelligent habits may secure the survival
of those organisms whose germ-plasm bears the seeds of favourable
congenital variations is not improbable. But in that case intelligent
procedure only contributes to the survival and not to the origin of
hereditary variations.
Crucial observations.
To test the hypothesis that natural selection is an essential condition
to the genesis of instinctive behaviour it should be the aim of
investigation to find crucial cases. This is, however, no easy task. We
ought to be able to adduce cases in which, where the incidence of
natural selection is excluded, acquired habits do not become
instinctive. But it is difficult to do so. It seems, however, that in
young chicks drinking from still water is a habit acquired through
imitation of the acts of the hen-mother. The presentation of such water
to sight does not evoke the appropriate instinctive response, while the
presentation of water taken into the bill does at once evoke a
characteristic response. Now it would seem that in the former case,
since the hen "teaches" all her chicks to peck at the water, she shields
them from the incidence of natural selection. But though the hen can
lead her young to peck at the water, she cannot "teach" them how to
perform the complex movements of mouth, throat and head required for
actual drinking. In this matter they are not shielded from the incidence
of natural selection. Thus it would seem that, where natural selection
is excluded, the habit has not become congenitally linked with a visual
stimulus; but where natural selection is in operation, the response has
been thus linked with the stimulus of water in the bill.
Imitation.
If this interpretation be correct we have here an example of the manner
in which imitation plays an important part in the formation of habits
which though oft-repeated are not transmitted as hereditary instincts.
But the imitative act is itself instinctive. The characteristic feature
of the imitative act, at the instinctive level, is that the presentation
to sight or hearing calls forth a mode of behaviour of like nature to,
or producing like results to, that which affords the stimulus. The
nature of instinctive imitation needs working out in further detail. But
it is probable that what we speak of as the imitative tendency is, in
any given species, the expression of a considerable number of particular
responses each of which is congenitally linked with a particular
presentation or stimulus. The group of instincts which we class as
imitative (and they afford only the foundations on which intelligent
imitation is based) are of biological value chiefly, if not solely, in
those species which form larger or smaller communities.