_INSTINCTIVE BEHAVIOUR_
I.--DEFINITION OF INSTINCTIVE BEHAVIOUR
There are probably few subjects which have afforded more material for
wonder and pious admiration than the instinctive endowments of animals.
“I look upon instinct,” wrote Addison in one of his graceful essays,
“as upon the principle of gravitation in bodies, which is not to be
explained by any known qualities inherent in the bodies themselves,
nor from any laws of mechanism, but as an immediate impression from
the first Mover and the Divine Energy acting in the creatures.”[21] In
like manner Spence said: “We may call the instincts of animals those
faculties implanted in them by the Creator, by which, independent of
instruction, observation or experience, and without a knowledge of
the end in view, they are all alike impelled to the performance of
certain actions tending to the well-being of the individual and the
preservation of the species.”[22] According to such views, instinct is
an ultimate principle the natural genesis of which is beyond the pale
of explanation. But similar views were, at the time these passages
were written, held to apply, not only to animal behaviour, but also
to animal structure. The development of the stag’s antler, or of the
insect’s wing, was also regarded as “an immediate impression from
the first Mover and the Divine Energy acting in the creatures.” This
view, however, is, neither in the case of structure nor in the case
of behaviour, that entertained by modern science. It is indeed an
expression of opinion concerning the metaphysics of instinct. Leaving
the question of ultimate origin precisely where it stood in the times
of Addison and of Spence, modern science seeks to trace the natural
antecedents of all natural phenomena, and regards structure and
behaviour alike as the products of evolution, endeavouring to explain
the manner of their genetic origin in terms of progressive heredity.
Omitting, therefore, all reference to problems which, however
important, are beyond the limits of scientific inquiry,[23] we may
take as a basis for further discussion Spence’s definition, according
to which the instincts of animals are those faculties by which,
independent of instruction, observation, or experience, and without
a knowledge of the end in view, they are all alike impelled to the
performance of certain actions tending to their own well-being and the
preservation of the species.
Let us first consider the reference of instinctive actions to
a _faculty_ by which animals are said to be impelled to their
performance. Paley also defined instinct as “a _propensity_ prior to
experience.” And unquestionably in the popular conception it is usual
to attribute instinctive acts to some such conscious cause. But it
will be more convenient, for the present, to consider instinctive
behaviour from the objective point of view, as it is presented to
our observation; we may then proceed to the further consideration of
the conscious concomitants which may be inferred. From the objective
point of view, therefore, we may agree with Professor Groos, who
says[24] that “the idea of consciousness must be rigidly excluded
from any definition of instinct which is to be of practical utility,”
since “it is always hazardous in scientific investigation to allow an
hypothesis which cannot be tested empirically.” In this we have the
support of Dr. and Mrs. Peckham, whose studies of the life-histories
of spiders and wasps are models of careful and patient investigation.
“Under the term Instinct,” they say, “we place all complex acts which
are performed previous to experience, and in a similar manner by all
members of the same sex and race, leaving out as non-essential, at
this time, the question of whether they are or are not accompanied by
consciousness.”[25]
It may be said, however, that some reference to the conscious aspect
of instinctive behaviour is implied by saying that the acts are
performed without instruction or experience. But the reference at
present is wholly negative. We may say, as the result of observation,
that instinctive acts are performed under such circumstances as exclude
the possibility of guidance in the light of individual experience, and
render it in the highest degree improbable that there exists any idea
of the end to be attained. But this is a very different position from
that of asserting the presence of a positive faculty or propensity
which impels an animal to the performance of certain actions. This it
is which, from the observational point of view, is unnecessary. For
the reference of a given type of observed behaviour to a “propensity”
so to behave or to a “faculty” of thus behaving, is no more helpful
than the reference of the development of any given type of structure
to a “potentiality” so to develop. We may, therefore, without loss of
precision, simplify Spence’s definition by stating that instinctive
behaviour is independent of instruction and experience, and tends to
the well-being of the individual and the preservation of the species.
Let us next consider the clause which affirms that instinctive
behaviour is prior to experience. This is well in line with the
distinction now drawn by biologists between congenital and acquired
characters. It refers them to the former category, and implies that
the organic mechanism by which they are rendered possible is of
germinal origin. This is not, however, universally admitted. Professor
Wundt, for example, approaching the subject from the point of view
afforded by the study of man and the higher animals, gives to the
term a wider meaning, and so defines instinct as to include acquired
habits. “Movements,” he says,[26] “which originally followed upon
simple or compound voluntary acts, but which have become wholly or
partly mechanized in the course of individual life, or of generic
evolution, we term _instinctive_ actions.” In accordance with this
definition, instincts fall into two groups. Those “which, so far as we
can tell, have been developed during the life of the individual, and
in the absence of definite individual influences might have remained
wholly undeveloped, may be called _acquired_ instincts.” They have
become instinctive through repetition. “To be distinguished from these
acquired human instincts are others which are _connate_.” Now, there
can be no question that behaviour which has become habitual through
frequent repetition is frequently, in popular speech, described as
instinctive. We hear it said that the experienced cyclist guides his
machine instinctively. And the word is similarly used in many like
cases. But we shall find it conducive to precision and clearness of
thought to emphasize the distinction between what is acquired in
the course of life and what is congenital in the race. And to this
end we shall regard behaviour which has “become mechanized in the
course of individual life” as due to acquired habit, reserving the
term _instinctive_ for such behaviour as is independent of individual
experience. We shall, in short, so far accept Spence’s definition.
In this definition, as in those of the majority of naturalists,
it seems to be further implied that instinctive behaviour is of a
relatively definite kind, though it is no doubt subject to such
variation as is found in animal structure and organization. Mr.
Rutgers Marshall, however, in a recent work,[27] protests against any
such implication, and urges that “this variableness is so wide that
definiteness of reaction cannot for a moment be used as a differentia
in relation to instinct without narrowing our conception of the bounds
of instinct in a manner to be deplored.” “The actions,” he says,
“connected with the preparation for self-defence, those connected with
protection of the young, with nest-building, with migration, etc.,
these actions are surely to be classed as instinctive; and yet they
are exceedingly variable and unpredictable in detail; all that we can
predict is the general trend of the varying actions which result from
varying stimuli under varying conditions, and which function to some
determinate biological end.”
Mr. Marshall then proceeds to argue that we are “warranted in speaking
of the ethical instincts, of the patriotic instincts, of the benevolent
instincts, and of the artistic instincts;” and thus leads up to the
position, to be further elaborated in his work, that there exists in
man a religious instinct which has fulfilled a function of biological
value in the development of our race. Now, here again there is much in
popular usage of the words _instinct_ and _instinctive_ which lends
support, for what it is worth, to Mr. Marshall’s very broad conception
of the range of instinct. Again and again we hear, in the pulpit and
elsewhere, of the religious instinct; we hear, too, of the benevolent,
patriotic, and artistic instincts, and more besides. But what we are
endeavouring to define is a type of behaviour which, as such, is
prior to instruction and experience. Can we affirm that patriotic and
religious behaviour conforms to such a type? Is it unquestionably
congenital and not acquired? If we are forced to give negative answers
to these questions we must regard Mr. Marshall’s conception of instinct
(one inclusive of multifarious tendencies which have a biological
value) as too broad and too vague to be of any service to us at this
stage of our study of animal behaviour.
What, then, shall we understand by Spence’s phrase that instinct
involves the performance of “certain actions”? And how far shall
we accept it? We shall take it as implying so much definiteness of
behaviour as renders instinctive acts susceptible of scientific
investigation, and in this sense shall accept it with some modification
of phraseology. We shall freely admit, however, the existence of
variations of instinctive behaviour analogous to variations in animal
structure. It is the occurrence of such variations that renders the
natural selection of instinctive modes of behaviour conceivable.
We shall also admit some, nay much, variation in detail. Take, for
example, two of the cases which Mr. Marshall cites--nest-building
and migration. Both involve, not merely a simple response to a given
stimulus, but a complex sequence of actions. In detail there may be
much variation even among members of the same species. And yet, can it
be questioned that the behaviour as a whole is in each case relatively
definite? May we not even say that it is remarkably definite? May we
not even go further, and assert that only on the assumption that any
given instinctive act is relatively definite, can we regard it as a
subject for scientific investigation, and can we hope to distinguish it
from other modes of behaviour?
The next point for consideration in Spence’s definition, which we
have taken as our text, is his characterization of instinctive acts
as “tending to the well-being of the individual and the preservation
of the species.” Here we have Mr. Marshall with us, for he too lays
stress on the fact that instinctive behaviour has reference to a
definite biological end. But in saying that the biological end is _the_
objective mark of an instinct,[28] he seems to be in error. Because,
in the first place, there are other “objective marks,” and because, in
the second place, this objective mark is not restricted to instinctive
behaviour. According to Spence, a further characteristic of instinctive
acts is that they are independent of instruction or experience; and
this serves to differentiate them from other modes of behaviour which
are also subservient to a biological end. Intelligent behaviour, not
less than that which we term instinctive, has reference to a biological
end. Many intelligent acts, for example, have for their object the
well-being of the individual; many subserve race preservation; these
bear, every whit as much as instinctive acts, the “objective mark”
which Mr. Marshall regards as characteristic of instinct. And if we
turn to his subjective criterion--the absence of any conception of
the biological end which the behaviour subserves--Mr. Marshall’s
position is equally untenable. There are thousands of acquired modes of
behaviour, dependent on instruction or experience, in which there is,
on the subjective side, so far as we can judge, no conception of the
biological end to be attained. What can the animal in the early stages
of intelligence know of biological ends? Mr. Marshall’s subjective
criterion applies just as much to a wide range of intelligent behaviour
as it does to instinctive actions.
In accepting, therefore, Spence’s statement that when animals
behave instinctively they perform, without a knowledge of the end
in view, certain actions tending to their own well-being and the
preservation of the species, we must take it in connection with the
preceding limitation, remembering that they are also performed without
instruction and experience.
A further point for very brief consideration is suggested by the
phrase in which Spence says that animals are _all alike_ impelled to
the performance of certain actions. As it stands it is too sweeping
and general. Still, we do require some explicit statement of the
facts which he had in mind when he wrote the words “all alike.” And
we find it with sufficient exactness in Dr. Peckham’s definition,
where he comprises under the category of instinctive behaviour “all
complex acts which are performed previous to experience, and _in a
similar manner by all members of the same sex and race_.” This places
congenital behaviour in line with morphological structure as a subject
for comparative treatment.
One more question remains. What shall we understand by “complex acts”?
In the first place, it is well to restrict the term instinctive
to _co-ordinated_ actions; and this implies the presence of
nerve-centres by which the co-ordination is effected. We thus exclude
the organic behaviour of plants, since there is no evidence in the
vegetable kingdom of co-ordinating centres. In the second place, the
co-ordination is, as we have seen, congenital, and not acquired in the
course of individual experience. Young water-birds, and indeed young
chicks, as soon as they are born, and have recovered from the shock
of birth, can swim with definite co-ordination of leg movements. Here
the definiteness is not only congenital, but _connate_, if we use the
latter term for an instinctive activity which is performed at or very
shortly after birth. On the other hand, young swallows cannot fly at
birth; they are then too immature, and their wings are not sufficiently
developed. But when they are some three weeks old, and the wings have
attained functional size and power, little swallows can fly with
considerable if not perfect skill. The co-ordination is congenital,
for it is not acquired in the course of individual experience; but it
is not connate, since it is not exhibited at or shortly after birth.
The term _deferred_ may be applied to such congenital activities as
are thus carried out when the animal has undergone a certain amount of
further development after birth.
In the third place, it is customary to distinguish between such reflex
actions as have already been briefly exemplified,[29] and instinctive
behaviour. It is, however, by no means easy, if indeed it be possible,
to draw any sharp and decisive line of demarcation. Instinct has indeed
been well described by Mr. Herbert Spencer as compound reflex action;
hence the distinction between instinctive and reflex behaviour turns in
large degree on their relative complexity. It would seem, however, that
whereas a reflex act--such as the withdrawal of the foot of a sleeping
child when the sole is tickled--is a restricted and localized response,
involving a particular organ or a definite group of muscles, and is
initiated by a more or less specialized external stimulus; instinctive
behaviour is a response of the animal as a whole, and involves the
co-operation of several organs and of many groups of muscles. Partly
initiated by an external stimulus or group of stimuli, it is also,
seemingly, determined in part, in a greater degree than reflex action,
by internal factors which cause uneasiness or distress, more or less
marked, if they do not find their normal instinctive satisfaction. This
point, however, may be more profitably discussed in connection with
the conscious aspect of instinct. If, then, we say that reflex acts
are local responses of the congenital type due to specialized stimuli,
while instinctive activities are matters of more general behaviour,
usually involving a larger measure of central (as opposed to local or
ganglionic) co-ordination, and due to the more widely-spread effects
of stimuli in which both external and internal factors co-operate, we
shall probably get as near as is possible to the distinction of which
we are in search. But it must be remembered that there are cases in
which the distinction can hardly be maintained.
We are now in a position to define instinctive behaviour as comprising
those complex groups of co-ordinated acts which are, on their first
occurrence, independent of experience; which 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 the 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 experience.
II.--INSTINCTIVE BEHAVIOUR IN INSECTS
Since instinctive behaviour is, by definition, independent of
experience, and since the animals which act instinctively are also, in
many cases, able to act intelligently, it is clear that, apart from
hereditary variations, we must expect to find acquired modifications
of instinct. As Huber said of bees, their instinctive procedure often
indicates “a little dose of judgment.” It is, indeed, exceedingly
difficult, as a matter of observation, to distinguish between
hereditary variation and acquired modification. For the _rôle_ played
by these two factors in any given behaviour can only be determined if
the whole life-history of the individual be known, and if there be
opportunities for comparing it with the complete life-histories of
other members of its race. And this is seldom possible.
These considerations must be borne in mind as we proceed to a brief
study of some of the instinctive modes of behaviour in insects.
Dr. and Mrs. Peckham’s investigations on the instincts and habits of
the solitary wasps have been described in a volume[30] worthy to be
placed by the side of Fabre’s “Souvenirs.” Their descriptions seem to
glow with the warm sunshine, and are redolent of the fresh air which
afforded the conditions under which the observations were conducted. We
can but regret that, in extracting from their bright pages some of the
salient facts, the natural delicacy and grace of their treatment must
be lost. For we can only give the dry skeleton which they have clothed
with the flesh of lively detail. They enumerate the following primary
modes of instinctive behaviour:--
1. Stinging.
2. Taking a particular kind of food.
3. Method of attacking and capturing prey.
4. Method of carrying prey.
5. Preparing nest, and then capturing prey, or the reverse.
6. The mode of taking prey into the nest.
7. The general style and locality of the nest.
8. The spinning or not spinning of a cocoon, and its specific form when
one is made.
When the young _Pelopœus_ emerges from the pupa-case and gnaws its
way out of the mud cell, with limp and flaccid wings, it responds
to a touch by well-directed movements of the abdomen with thrusts
of the sting, as perfect as those of the adult. There is clearly no
opportunity here for either instruction or experience to afford any
intelligent guidance. Stinging is an instinctive act. And it is an act
of which great use is made in the capture of prey which shall serve for
food to the young--it has a biological end. But the wasps of different
species do not have to learn by experience what prey to attack. It
is by instinct, too, that they take their proper food-supply, one
caterpillars, another spiders, a third flies or beetles. So deeply
seated, indeed, is the hereditary preference, that no fly-robber ever
takes spiders, nor will the capturer of spiders change to caterpillars
or beetles. Some keep to a few species or genera, while _Philanthus
punctatus_ preys chiefly or entirely on bees of the genus _Halictus_.
Romanes[31] thought that the manner of stinging and paralyzing their
prey might “be justly deemed the most remarkable instinct in the
world.” Spiders, insects, and caterpillars are stung, he says, “in
their chief nerve-centres, in consequence of which the victims are not
killed outright, but rendered motionless; they are then conveyed to a
burrow and, continuing to live in their paralyzed condition for several
weeks, are then available as food for the larvæ when these are hatched.
Of course the extraordinary fact which stands to be explained is that
of the precise anatomical, not to say also physiological knowledge
which appears to be displayed by the insect in stinging only the
nerve-centres of its prey.” Eimer[32] thought that it “is absolutely
impossible that the animal has arrived at its habit otherwise than by
reflection upon the facts of experience.” “At the beginning,” he says,
“she probably killed larvæ by stinging them anywhere, and then placed
them in the cell. The bad results of this showed themselves; the larvæ
putrified before they could serve as food for the larval wasps. In the
mean time the mother wasp discovered that those larvæ which she had
stung in particular parts of the body were motionless but still alive,
and then she concluded that larvæ stung in this particular way could be
kept for a longer time unchanged as living motionless food.”
Now, since these wasps, when they have stored their nests and laid an
egg on one of the victims, close it up once and for all, and take no
further interest in it or its contents, there seems no opportunity,
at any rate in the existing state of matters, for the acquisition of
that experience on which Eimer relied. But both his explanation and
Romanes’s difficulty are based on the following assumptions: first,
that the victims are instinctively or habitually stung in the chief
nerve-centres; secondly, that when thus stung they are not killed
but remain paralyzed for weeks; and thirdly, that the marvellously
definite and delicate instinctive behaviour is in direct relation to
the uniform result of prolonged paralysis and consequent preservation
of the food in the fresh state. But Dr. Peckham’s 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 paralyzed live for a varying number of days, some more, some
less; that wasp larvæ thrive just as well on dead victims, sometimes
dried-up, sometimes undergoing decomposition, as on living and
paralyzed 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.
“We believe,” he says, “that the primary purpose of the stinging is to
overcome resistance, and to prevent the escape of the victims, and that
incidentally some of them are killed and others are paralyzed.”
If, therefore, as will probably be shown to be the case, these
conclusions are found to be generally true for this interesting group
of insects, the mystery of “the precise anatomical, not to say also
physiological knowledge which appears to be displayed” by these wasps
turns out to be one of our own fabrication. It melts away in the light
of fuller and more searching investigation.
[Illustration: FIG. 11.--Solitary Wasp stinging Caterpillar (after
Peckham).]
It must not be supposed, however, from what has been said, that the
behaviour in the act of stinging is altogether indefinite. On the
contrary, each species proceeds in a relatively definite manner with
some variation or modification of method. _Philanthus punctatus_, for
example, stings the bees, on which she preys, under the neck, and the
thrust is at once fatal. Dr. Peckham further notes that he was only
successful in getting the wasps to sting when they were hunting; those
that had not yet begun to store the nests paid no attention to the
bees. This is an example of that internal factor to which reference was
made in the last section. Marchal observed that _Cerceris ornata_ runs
the end of her abdomen along the under surface of the thorax of the
bee, and delivers her thrust at the division of the segments--that is,
where the sting can enter. The action does not imply any physiological
knowledge. In general she begins at the neck. Spiders are usually, but
not always, stung on the ventral surface. To give but one more example,
Dr. Peckham observed in three cases the procedure of _Ammophila
urnaria_ which preys on caterpillars, and often, after stinging, bites
the neck in several places, this process being termed malaxation. In
three observed captures, all the caterpillars being of the same species
and alike in size, the thrusts were given on the ventral surface near
the middle line, between the segments. In the first, seven stings were
given at the extremities (there being thirteen segments), the middle
segments being left untouched, and no malaxation was practised. In the
second, seven stings were again given, but in the anterior and middle
segments, followed by slight malaxation. In both these cases the first
three thrusts were in definite order, behind the third, the second, and
the first segments successively. In the case of the third caterpillar,
only one thrust was given, between the third and fourth segments--that
is to say, in the position of the first stab in the other cases,--and
after this one thrust there was prolonged malaxation. Of fifteen stored
caterpillars examined, some lived only three days, others a little
longer, while a few showed signs of life at the end of a fortnight. In
more than one instance the second of the two caterpillars stored in
each nest died and became discoloured before the first one was entirely
eaten. The larva under such circumstances ate it with good appetite,
and then spun its cocoon as if nothing unpleasant had occurred.
[Illustration: FIG. 12.--Solitary Wasp dragging a Caterpillar to its
Nest (after Peckham).]
The mode of carrying their booty is in these wasps instinctive, and
relatively uniform. _Ammophila urnaria_ grasps the caterpillar, near
the anterior end, in her mandibles, and carries or drags it beneath her
legs, walking forwards. It is generally but not always with the ventral
surface uppermost. _Pompilus_ takes hold of her spider anywhere, but
always drags it over the ground, walking backwards. _Oxybelus_ clasps
her fly with her hind legs; _Bembex_ with the second pair. Each works
after her own fashion in a way that is relatively uniform for each
species.
The general style of the nest, its mode of construction, and its method
of closure, are always performed, says Dr. Peckham, by each species
in a similar manner, not indeed in circumstantial detail, but quite
in the same way in a broad sense. Variation or modification is always
present, but the tendency to depart from a nest of a given type is not
excessive. Some dig in the ground curved tunnels, with or without one
or more chambers. Others bore into decaying wood; others use straws,
or make tunnels in bramble stems; while the mud-daubers build cells in
which to store the food and lay the egg. This is sometimes deposited
on the first, sometimes on the last, sometimes on some intermediate
victim, but generally in much the same place and position. _Ammophila_,
for instance, lays it on the side of the sixth or seventh segment--that
is to say, in about the mid position.
Some species first capture their prey, and then make the nest in which
it is to be entombed. Others first prepare the nest, and then carry
or drag their prey to it--often from considerable distances--quite
irrespective of what seems to us the more appropriate method of the
two under the particular circumstances of the case. And the way in
which the victim is dragged into the nest is similarly a matter of
inheritance. Each way is characteristic of the species concerned, and
would be an important part of any definition of the animal based upon
its modes of behaviour. For example, a _Sphex_ places her grasshopper
just at the entrance of the nest, which she then enters herself before
dragging in her prey by the antennæ. When the wasp was in the hole,
Fabre moved the victim a little way off; the wasp came out, brought
the grasshopper to the entrance as before, and went in a second time.
This was repeated about forty times, each time with the same result,
until the patience of the naturalist was exhausted, and the persistent
wasp took her booty in after her appropriate fashion. She must place
the grasshopper close to the opening; she must then descend and examine
the nest, and, after that, must drag it down. Nothing less than the
performance of these acts in a certain order satisfies her instinctive
impulse.
In a private letter, from which he kindly allows me to quote, Dr.
Peckham says: “We have recently made some experiments on this wasp
(_Sphex ichneumonea_). First we allow her to carry in her prey
undisturbed, to see how far she was faithful to the traditions of her
ancestors, and to observe her normal methods. On the next day, when she
had placed her grasshopper just at the opening of the nest, and while
she was below, we drew it back to a little distance. She came out, and
we both repeated our operations four times--she running down into the
nest, always after getting the grasshopper into position, and we as
regularly drawing it away. The fifth time she changed her plan, seized
it by the head and backed into the nest with it. The next day, at the
fourth trial, she straddled it and walked head first into the nest with
it; and on the fourth day, at the eighth trial, she backed in with it
as on the second day.” These interesting observations show that the
wasp has sufficient intelligence to modify her procedure in accordance
with an unwonted situation. The “consecutive necessity,” as it has been
termed, has a potent influence, but is not absolute.
Fabre notes a case of similar consecutive necessity in the case of the
mason bee, _Chalicodoma_. If while a bee is provisioning its nest with
honey and pollen the structure be destroyed, she sometimes breaks open
a completed cell, and, having done so, goes on bringing more provision,
though the cell already contains a sufficient store of food; and only
when she has completed the superfluous storing does she deposit her egg
and seal up the cell. So, too, when the cell is removed in an early
stage of construction, and another completed cell already partially
stored is substituted, the bee, instead of simply adopting the new
cell, goes on building until the cell is as much as one-third beyond
the usual height; then, and not till then, does she proceed in due
course to the next stage of the instinctive procedure, the provisioning
of the cell.
From our general knowledge of animal nature, we should expect to
find parasitic forms ready to take advantage of the material stored
by such insects as the solitary wasps and the mason bees. It is said
that _Chalicodoma_ provides nourishment to the larvæ of some sixteen
unbidden guests. A parasitic bee (_Stelis nasuta_) breaks open a
closed cell, and, after depositing its eggs, seals it up again with
mortar. Since her eggs and larvæ develop more rapidly than those of
the mason bee, they are first served with the store of provision,
while the rightful owner is done out of its inheritance. By a curious
act, of what appears to us like retributive justice, these parasitic
larvæ sometimes fall a prey to another parasite, also a hymenopterous
insect named _Monodontomerus_, the larvæ of which prey on the young
of both bees. Another genus of the same family, _Leucopsis_ (Fig. 13,
F), also succeeds in piercing with its ovipositor, at a suitable spot,
the walls of the _Chalicodoma_ cell, and suspends its curious hooked
egg (Fig. 13, G) on the delicate cocoon within which the chrysalis
lies. Fabre found in some cases as many as five of these parasitic
eggs on a single cocoon. But he never found more than one larva in any
cell that he examined. The following is an epitome of his conclusions
and inferences. From the parasitic egg is hatched a minute arched
grub, with relatively large head and mandibles, and provided with
a number of bristles, which aid it in progression (Fig. 13, H). It
does not, however, at once attack the bee larva, but makes a series
of excursions, the object of which is to reach and destroy any other
parasitic eggs. This was not actually observed, but the eggs were
found to have been destroyed, and there was seemingly no other means
of destruction under the conditions maintained. The larva, this done,
changes its skin and takes on a new form, destitute of bristles, with a
very small head and minute mandibles (Fig. 13, I). In this new form it
attacks the _Chalicodoma_ larva, making a very small incision, through
which the juices of the host are transferred to the guest without
further injury to the grub. It is interesting to note that, if the
facts are accurately described and the inferences are correct, there
are associated with two types of instinctive behaviour two distinct
types of structure. The creature can have no conscious control over its
structural development, and there is no ground for assuming that it has
any control over its instinctive behaviour.
[Illustration: FIG. 13.--Insect Larvæ. A, B, of _Sitaris_; C, D, E, of
_Argyromœba_; G, H, I, of _Leucopsis_; F, imago of _Leucopsis_ (after
Fabre).]
The specialization of structure and of instinctive behaviour, in
accordance with a definite sequence of life-conditions, is even more
remarkable in another of the many parasites which _Chalicodoma_
unwittingly labours to nourish. This time it is a fly (_Argyromœba_),
which lays a minute egg on the outside of the cell. From this egg is
hatched a slender threadlike worm, barely one-twentieth of an inch in
length (Fig. 13, C). It has three pairs of longish bristles near the
anterior end, and a single yet longer pair at the hinder extremity.
These aid it in creeping over the wall of the cell. Its small head
is armed with short, stiff bristles. For many days it wanders over
the surface of the cell, inserting its bristly head into each minute
cranny and crack. Throughout this long period it has never a bite nor
sup. Probably many of them never succeed in finding a crevice by which
they can effect an entrance, but those that do manage to wriggle in
undergo a change, lose their bristles, and develop a minute suctorial
mouth, through which the contents of the larva are absorbed into their
swelling bodies (Fig. 13, D). When fully grown they are quite helpless,
and unable to get out from the cell in which they are now imprisoned.
For months they lie quiescent, but in the succeeding spring they pass
into a pupal condition very different from that of most flies. The
relatively large head is armed with strong spines; the middle region
bears bristles directed backwards; the posterior end has short spines
(Fig. 13, E). Fixing itself to the interior of the cell by the latter,
it strikes with its armoured head repeated blows on the walls of its
prison until a breach is at last made, and sufficiently enlarged to
form a suitable exit. Then the pupa-skin bursts, and the imago insect
emerges and flies off. At each stage of life there is the closest
relation between structure and behaviour, and each is equally adapted
to a biological end of which the creature has never had an opportunity
of gaining any experience.
Exceedingly multifarious are the ways in which insects thus provide
for the future of young they will never see. _Antherophagus_ lives
in flowers, and is believed to seize with its mandibles humble bees,
which then unwittingly bear the parasitic beetle to the nests in which
alone the larvæ have been found. The larvæ of our common oil-beetle
(_Meloë_) are parasitic on the bee, _Anthophora_. It deposits its ten
thousand eggs without observable discrimination; but the active young
larva instinctively seizes and attaches itself to any hairy object.
Thousands must go astray. They have been found on hairy beetles, flies,
and bees of the wrong genus. Some, however, become thus attached to
the one suitable species, and are conveyed by the _Anthophora_ to her
nest, where they promptly eat the egg she lays. It is not difficult
to picture to one’s self how this incompletely evolved instinct might
be further perfected by natural selection, through the survival of
those females which laid their eggs in the haunts of the bee-host. And
such an advance in instinctive behaviour is seen in another and rarer
beetle--_Sitaris_. Her eggs are laid in August near the entrance to a
nest of the _Anthophora_. In September they hatch to form larvæ, which
hibernate in groups till the following spring. Then they become active
(Fig. 13, A), and attach themselves to hairy objects. Being near the
_Anthophora_ nest, there is an increased chance of their fastening upon
this bee. The chance is still far from good, for if this were so, we
should not find that the _Sitaris_ laid as many as two thousand eggs.
Still, on these grounds, we may presume that its chance of survival is
about five times as good as that of _Meloë_, which lays ten thousand
eggs. The larva is said generally to attach itself to a male bee, which
is hatched earlier than his mate, and to pass on to the female at the
nuptial period; but in any case it eventually slips on to the egg that
she lays. This forms the food of the larva during the remainder of this
stage of its existence. It then moults and assumes a new form, capable
of feeding on the honey (Fig. 13, B); and, after further changes,
becomes a pupa, and then assumes the imago condition.
In these cases the advantage is wholly on the side of the parasite. But
there are cases of close relationship between insects and flowering
plants where the instinctive behaviour gives rise to reciprocal
benefit. The Yucca is a genus of American Liliaceous plants, with large
pale sweet-smelling flowers; and these are dependent for fertilization
on the instinctive behaviour of a small straw-coloured moth of the
genus _Pronuba_. Just when the Yucca plant blossoms in the summer,
the moths emerge from their chrysalis cases. They mate; and the
female then flies to a flower, collects a pellet of pollen from the
anthers, proceeds to another flower, pierces the pistil with her sharp
ovipositor, lays her eggs among the ovules, and finally darting to the
stigma stuffs the pollen pellet into its funnel-shaped extremity (Fig.
14). If the flower be not thus fertilized the ovules do not develop;
and if the ovules do not develop the grubs which are hatched from the
moth’s eggs die of starvation. There are enough ovules to supply food
to the grubs, and leave a balance to continue the race of Yuccas.
[Illustration: FIG. 14.--Yucca Flower and Moth.]
Whether the female moth is attracted to the flower by sight or smell,
we do not know. And whether the male finds the female, in the case
of the Yucca moth, through scent, we are not in a position to state
with certainty. It has, however, been shown that in certain moths[33]
some odour emitted by the female is the attractive stimulus, affecting
sense-organs situated on the antennæ of the male. To females confined
in an opaque vessel over the mouth of which gauze was tied, the males
came in numbers; but when a clear glass vessel was inverted, and sand
was packed round the mouth, so as to prevent the escape of air from the
interior, no males came, though the imprisoned females were clearly
visible. If the antennæ of the males were either removed or coated with
shellac the moths failed to notice the females even when close to them.
In what way the intact male is made aware of the direction from which
the scent comes, we do not know--possibly by differential stimulation
in the antennæ, the moth instinctively turning in the direction of
greater stimulation. It will be seen, therefore, that in the case of
the behaviour of the Yucca moth--behaviour which is essential to the
biological end of reproduction--there is much detail concerning which
we are ignorant. But for our present purpose the important point to
notice is that the procedure of the female cannot be due to imitation;
nor can it be the outcome of individually acquired experience; for
the method of procedure is not gradually learnt, but is carried out
without apparent hesitation the first and only time the appropriate
occasion presents itself. Not only does the moth take no heed of her
grubs, but they are so placed that she could not in any case ascertain
by observation that only if the ovules are fertilized do her offspring
thrive. She cannot possibly know what effect the stuffing of the pollen
on to the stigma exercises, or indeed whether it have any effect at
all. And yet generation after generation these moths collect the pollen
from the anthers and bear it to the stigma. Spence’s words “without
knowledge of the end in view” are amply justified in this case, as in
other cases of typically instinctive behaviour.
III.--THE INSTINCTIVE BEHAVIOUR OF YOUNG BIRDS
Since it is easy to hatch birds of many species in an incubator, and
to rear them under conditions which not only afford facilities for
observation but exclude parental influence, their study has special
advantages. One can with some approach to accuracy distinguish the
instinctive from the acquired factors in their behaviour.[34]
[Illustration: FIG. 15.--Newly-hatched Chick swimming.]
The callow young of such birds as pigeons, jays, and thrushes are
hatched in a helpless condition, and require constant and assiduous
ministration to their elementary organic needs. Most of their instincts
are of the deferred type. But pheasants, plovers, moor-hens, domestic
chicks, and ducklings, with many others, are active soon after birth,
and exhibit powers of complex co-ordination, with little or no
practice of the necessary limb-movements. They walk and balance the
body so soon and so well as to show us that this mode of procedure is
congenital, and has not to be gradually acquired through the guidance
of experience. Young water-birds swim with neat and orderly strokes the
very first time they are gently placed in water. Even little chicks a
day or two old can swim well. Dr. Thorndike, who draws attention to
this fact,[35] appears to accept the view, suggested by Dr. Bashford
Dean, that the movements are not those of swimming but only of running.
I have carefully watched the action through the glass walls of a tank
and compared it with that of a young moor-hen. In the two cases it
is quite similar in type, and the type appears to be different from
that of running, though it is perhaps hard to distinguish the two.
In any case, the hand over hand action is well co-ordinated, and is
very different from a mere excited struggle. Chicks twenty-six hours
old taken straight from the incubator drawer, before they had taken
food, made directly for the side of the tank and tried to scramble out.
They gradually sank deeper through the wetting of the down, but could
keep afloat for from two to three minutes. I have made observations on
chicks of various ages from twenty-four hours to a month, and find in
all cases similar results; but with the older birds the flapping of
the wings and more vigorous action cause them to get water-logged more
rapidly. There is some apparent distress with cries; but less than one
might expect under the circumstances. For the purposes of the above
illustration Mr. Charles Whymper had before him a sketch I made of the
leg-action, and instantaneous photographs of the chicks swimming for
which I am indebted to my colleague Mr. George Brebner. I have not
observed the behaviour of an adult hen when placed in the water. Dr.
Thorndike says, “there is no vigorous instinct to strike out toward the
shore,” she “will float about aimlessly for awhile and only very slowly
reach the shore.” But Mrs. Foster Wood informs me that she has seen a
hen leap into a pond after her brood of ducklings and swim to the other
side, a distance of twenty feet.
Diving, in water-birds, is also an instinctive mode of behaviour; and
this is obviously a more difficult procedure than swimming, one further
removed from reflex action. And careful observations have placed beyond
question the fact that flight is also instinctive. A swallow, for
example, taken from the nest under conditions which made it practically
certain that it had never yet taken wing, exhibited guided flight, and
attempted to alight on a suitable ledge. Of course flight is generally
a deferred instinct, and is not performed until the wings have reached
a suitable state of development. An instinctive response, which may
perhaps be regarded as one of its initial stages, is seen in quite
young chicks. If placed in a basket, and rapidly lowered therein
through a foot or two, the chick will extend its skinny and scarcely
feathered wings. But though, from the usual conditions of development,
flight in birds is a deferred instinct, yet in exceptional cases it
may be connate. The mound-builders (_Megapodes_) of the Australian
region are hatched from large eggs in warm earth or sand, and are not
tended by the parents. So well fledged are these birds that they can
fly the day they emerge from the egg. Dr. Worcester, while digging in
one of their mounds, made an unsuccessful attempt to seize one which
was newly hatched; but it flew several rods into thick brush, and this
notwithstanding the fact that it had probably never before seen the
light of day.
[Illustration: FIG. 16.--Nestling Megapode, to show the well-developed
wings. (From Dr. R. Bowdler Sharpe’s “Wonders of the Bird World.”)]
It must not be supposed that, in adducing flight as an example of
instinctive behaviour in birds, we are contending that it is this and
nothing more throughout life. The inference to be drawn from the facts
of observation is rather that instinct provides a general ground plan
of behaviour which intelligent acquisition, by enforcing here and
checking there, perfects and guides to finer issues. Few would contend
that the consummate skill evinced in fully developed flight at its
best, the hurtling swoop of the falcon, the hovering of the kestrel,
the wheeling of swifts in the summer air, the rapid dart and sudden
poise of the humming bird, the easy sweep of the sea-gull, the downward
glide of the stork--that these are, in all their exquisite perfection,
instinctive. A rough but sufficient outline of action is hereditary;
but the manifold graces and delicacies of perfected flight are due to
intelligent skill begotten of practice and experience.
There are many little idiosyncracies and special traits of flight
which are probably instinctive--such as enable an ornithologist or a
sportsman to recognize a flying bird from a distance. And the same is
true of other modes of behaviour. The observer of young birds cannot
fail to note and to be impressed by many of these. The way in which a
little moor-hen uses its wings in scrambling up any rough surface is
very characteristic; so, too, is the manner in which a guinea-chick
runs backwards and then sideways at a right angle when one attempts to
catch him. If suddenly startled, moor-hens and chicks scatter and hide;
plovers drop and crouch with their chins on the ground; pheasants stand
motionless and silent. Knowledge of the ways of birds enables one to
predict with tolerable accuracy how each kind will behave under given
circumstances. That the actions are always precisely alike cannot be
said with truth; but that the behaviour is so relatively definite as to
be readily recognizable can be confidently asserted. That a moor-hen
will flick its tail, that a chick will dust itself in the sand, that
pheasants and partridges will scratch the ground, that a jay will go
through certain actions in the bath, that the preening of the down will
be carried out in particular ways--moor-hens, for example, wringing out
the water in a peculiar manner,--and that all these, and many other
modes of behaviour, will be presented in relatively definite ways: all
these are, to borrow a phrase of Dr. Peckham’s, so characteristic of
the several groups of birds, that they would be an important part of
any definition based upon behaviour. And there can be no question that
they are instinctive. They may indeed seem trivial and commonplace,
scarcely worthy of special note; but they serve to show in how many
details organic heredity lays the foundation for future behaviour, and
affords groups of data for effective consciousness to utilize.
To show the instinctive nature of such behaviour, the following
examples will suffice. One of a batch of moor-hen chicks showed once,
and once only, when a week old, an incipient tendency to bathe in the
shallow tin of water which was placed in their run, but soon desisted;
nor was the action repeated, though he and the others enjoyed standing
in the water. Five weeks later one of the batch was taken to a beck.
He walked quietly through the comparatively still water near the edge;
but when he reached the part of the stream where it ran swiftly and
broke over the pebbles, he stopped, ducked, and took an elaborate bath,
dipping his head well under, flicking the water over his back, ruffling
his feathers, and behaving in a most characteristic manner. Each day
thereafter he did the same, with a vigour that increased up to the
third morning, and then remained constant. The same bird some weeks
later was swimming in a narrow part of the stream, with steep banks
on either side, when he was frightened by a rough-haired pup. Down he
dived, for the first time in his life; and after a few seconds his head
was seen to appear, just peeping above the water beneath the bank.
Ten days after receiving two nestling jays I placed in their cage a
shallow tin of water. They took no notice of it, having never seen
water before; for they were fed chiefly on sopped food. Presently one
of them hopped into it, whether attracted by the water or by accident
it is difficult to say, squatted in it bending his legs, and at once
fluttered his feathers, as such birds do when they bathe, though his
breast scarcely touched the water. The other seized the tin in his
bill, and then pecked at the water, thus wetting his beak. He, too,
fluttered his feathers in a similar fashion, though he was outside the
tin and not in the water at all. A little later the first again entered
the tin, and dipped his breast well into the water; this was followed
by much fluttering and splashing. The bird took a good bath, as did the
other shortly afterwards, and then spent half an hour in a thorough
grooming, with much fluttering of the wings, the crest feathers being
constantly raised and lowered, expressive of an emotional state.
Now, in these cases it would be impossible to say whether the behaviour
was carried out in the manner characteristic of the species, prior to
experience and independent of imitation, on the basis of mere casual
and chance observation. But in these cases the whole life-history
of the individuals concerned was known; and it can be asserted with
confidence that the behaviour was hereditary, and not acquired by any
gradual process of learning. Moreover, in each case there seemed to
be such evidence as observation can afford, that internal emotional
factors co-operated with the direct external stimuli in determining
the nature of the behaviour. Whether such actions so far contribute
to the well-being of the individual as to be of decisive advantage it
is difficult to say. Some would contend that bathing is practised by
birds merely for the pleasure it seemingly affords; others would urge
that it is a means of getting rid of troublesome and presumably hurtful
parasites, to the attacks of which birds are peculiarly subject.
[Illustration: FIG. 17.--Young Cuckoo ejecting nestling Meadow Pipit.
(From Mrs. Hugh Blackburn’s sketch in “Birds from Moidart.”)]
One of the most remarkable instincts of young birds is that of
the cuckoo, which ejects eggs and nestlings from the home of its
foster-parent. Mrs. Hugh Blackburn found a nest which contained two
meadow-pipits’ eggs, besides that of a cuckoo. On a later visit “the
pipits were found to be hatched, but not the cuckoo. At the next visit,
which was after an interval of forty-eight hours, we found the young
cuckoo alone in the nest, and both the young pipits lying down the
bank, about ten inches from the margin of the nest, but quite lively
after being warmed in the hand. They were replaced in the nest beside
the cuckoo, which struggled about until it got its back under one of
them, when it climbed backwards directly up the open side of the nest,
and hitched the pipit from its back on to the edge. It then stood quite
upright on its legs, which were straddled wide apart, with the claws
firmly fixed halfway down the inside of the nest, among the interlacing
fibres of which the nest was woven, and, stretching its wings apart and
backwards, it elbowed the pipit fairly over the margin, so far that
its struggles took it down the bank instead of back into the nest. As
it was getting late, and the cuckoo did not immediately set to work
on the other nestling, I replaced the ejected one and went home. On
returning next day, both nestlings were found dead and cold, out of
the nest.”[36] Here we have a definite account by an eye-witness, who
sketched the young cuckoo, which was naked, blind, and could scarcely
hold up its head. And her account, itself confirmatory of that given
by Jenner in 1778, is confirmed by that of Dr. John Hancock,[37] who
witnessed the ejection of a fledgling hedge-sparrow, which “was put
over the edge of the nest exactly as illustrated by Mrs. Blackburn.”
The procedure is unquestionably instinctive.
The sounds uttered by young birds are sufficiently definite to be
readily recognized and are susceptible of classification. In domestic
chicks at least six notes may be distinguished. First the gentle
“peeping” note, expressive of contentment. A further low note, a double
sound, seems to indicate extreme satisfaction and pleasure. Very
characteristic and distinct is the danger-note--a sound difficult to
describe, but readily recognized. If a humble-bee, a black-beetle, a
big worm, a lump of sugar--anything strange and largish--be thrown to
the chicks, this danger-note is at once heard; and it serves to place
others on the alert, though this is perhaps the outcome of experience.
Then there is the cheeping sound, expressive apparently of a state of
mild dissatisfaction with the present state of affairs. It generally
ceases when one throws some grain, or even stands near them. Extreme
dissatisfaction is marked by a sharper, shriller squeak, when one
seizes them against their inclination. Lastly, there is the shrill
cry of greater distress, when, for example, their swimming powers are
subjected to critical examination. With pheasants a gentle, “peeping”
note of contentment, a shriller cry of distress, and a danger-note,
generically like, but specifically distinct from, that of the chick,
are early differentiated. The complaining note of the partridge is
uttered six or seven times in quick succession, followed by a pause.
The note of the plover is high-pitched, and much like the familiar
cry of the adult bird, to which it owes its popular name of “peewit.”
So, too, the guinea-fowl in down utters from the first notes quite
characteristic of its kind, while its danger-note is not unlike that
of the chick or pheasant. The piping of ducklings is comparatively
monotonous, and there does not seem to be a definite danger-note. With
moor-hen chicks, even on the first day, two notes are well-marked--a
call-note, lower in pitch than that of the chick, and rather harsh and
raucous, and a “tweet, tweet” of pleasure, something like the contented
note of a canary. Later, five or six notes are differentiated, the most
characteristic of which is the harsh “crek, crek,” when the little bird
is from any cause excited. It is uttered in a crouching attitude, with
head thrown back and wings held outwards and forwards, waving to and
fro in a very characteristic manner. That this has suggestive value for
other moor-hen chicks is shown by its distinctly infectious effect; if
one bird has cause to utter the note and strike the attitude others
follow suit. While clearly instinctive in their mode of occurrence,
while they seem to show well the co-operation of an internal emotional
factor, their biological value seems to lie in their suggestive effect
on other members of the brood. They form an elementary but sufficient
social bond.
If these notes afford evidence of an incipient social factor, the
instinct of pecking is distinctively individualistic. Chicks peck
with considerable but not complete accuracy of aim at practically
anything of suitable size at suitable distance; but it is through
experience that they learn what to select for food and what to reject
or leave untouched. Moving objects, however, are more readily pecked
at than those which are still; and the instinctive response seems to
be stimulated if one tap on the ground near the object, or move it
with a pencil, thus simulating the action of the hen. And this is even
more marked with pheasants and partridges. Plovers seize small worms
with an avidity which looks like an inherited response to the sight
of natural food. Pheasants and partridges also appear to be specially
affected by worms, and when one of them seizes a worm for the first
time, he shakes it and dashes it against the ground. Chicks, a week or
ten days old, also seize a largish fly or bee with a dash, and maul it
on the ground, throwing it on one side before again approaching it.
And such birds seem to show an instinctive tendency to bolt with such
treasures as caterpillars or small worms. Moor-hens cannot at first be
induced to take food from the ground. It has to be held above them,
whereupon they crouch down, with head and neck held back, opening
their beaks more like the callow young of nursling birds; but they
also strike upwards at the object--these modes of behaviour being, no
doubt, correlated with the manner in which the mother moor-hen normally
feeds her young from her beak during the early days of life. Callow
fledglings, such as young jays, simply open their mouths, gaping widely
to be fed. And many will respond in this way to such a note as a low
whistle, as may readily be seen with swallows. But at a later age such
birds show instinctive modes of reaction of a more complex type. A jay,
for example, was offered a summer chafer or June bug, seized it at once
in his bill, and tried to place his foot on it. Then he hopped down on
to the floor of his cage, dropped the beetle, seized it again as it
crawled off, and after two or three attempts swallowed it, tossing it
back from the point of his bill into the throat. This was the first
time he took food from the ground or swallowed it in this manner.
On the whole, there seems to be much inherited definiteness of
co-ordination, and some tendency to respond in a definite manner to
specific stimuli. That there should not be more differentiation in
this respect than observation discloses is probably due to the fact
that the parent birds afford, under natural conditions, much guidance
in the selection of food. Since the solitary wasp unerringly seizes
its appropriate food, since it responds instinctively to specific
stimuli, there would seem no reason why birds should not show similar
instinctive differentiation. But one must remember that in the
case of the wasp there is no parental guidance; the insect is more
completely dependent on instinct than is the bird to whose needs the
hen assiduously ministers.
It is at first sight surprising that such birds as chicks and pheasants
do not peck instinctively at still water. When a shallow vessel
containing water was placed among some little chicks, several of them
ran repeatedly through the water, but took no heed of it. Then, after
about an hour, one of them standing in the vessel pecked at his toes,
and at once lifted his head and drank freely with characteristic
action. Another subsequently pecked at a bubble near the edge, and
then he too drank. In fact, the best way of inducing them to drink is
to scatter some grains of food in the tin; they peck at the grains,
which catch their eye, and incidentally find the water, and the touch
of water in the bill at once leads to the characteristic response and
congenitally definite behaviour. That the sight of a still surface does
not itself suffice to evoke this behaviour is probably again due to the
fact that under nature the hen guides them and pecks at the water, when
they follow her lead.
One fact which must be constantly borne in mind is that what is
inherited is instinctive co-ordination, often related to a definite
stimulus, not instinctive knowledge. A chick pecks at a grain when it
is at a suitable distance, not because instinct provides him with the
knowledge that this is something to be seized and tested, but because
he cannot help doing so. He is so organized that this stimulus produces
that result through an organic co-ordination that is independent of
conscious knowledge or experience. How definite is the inherited
co-ordination is shown by many observations. A young pheasant, only a
few hours old, was taken from the incubator drawer, and held snugly
while a piece of egg-yolk was moved before his eyes with the aid of
fine forceps. He did not peck at it, but followed with movements of
his head every motion of the object in a narrow circle. Simple as
this action seems, it presents a striking example of co-ordinated
movements accurately related to movements in the visual field, the
whole performed without any opportunity for learning or practice, and
less than half an hour after the bird was taken from the drawer of the
incubator and first saw daylight. Psychologists sometimes puzzle their
heads over the question how and by what steps the field of vision and
the field of movement are brought into relation with each other; but in
such a case as this, the problem ceases to be primarily psychological.
The relation is purely organic; the conscious data are grouped from the
outset. With young jays there was no such co-ordination at first; and
when they began after a few days (about twelve or fourteen) to follow
an object with the head and eye, the movements were at first jerky. But
a week later, when I swept the food through a circle a foot in diameter
in front of their cage, it was followed smoothly and evenly. Here a
certain amount of learning and practice, absent in the case of the
pheasant, was required. And it is difficult to say what proportion of
the final result was acquired, what proportion hereditary; but probably
the behaviour is in the main instinctive, though somewhat deferred.
One more example, perhaps even more trivial in the eyes of some
people, may be given. A duckling a few hours old will scratch the side
of his head. It is true he may topple over in the process, through
insufficient powers of balance, for the simultaneous performance of
poising on one leg and having a good scratch with the other is no easy
matter. But let not either our familiarity with such behaviour, nor
some observed and laughable failure on the part of the duckling, blind
us to the fact that this is a congenital activity, and one of no little
complexity, indicating a definite organic nexus. A local irritation
sets agoing movements of the hind limb of that side through which
just that particular spot is scratched in the absence of any previous
practice, any learning to localize the spot. There can be no question
that such inherited co-ordinations, whether perfect from the first,
or with deferred perfection and some aid from acquisition, afford
ready-made data to consciousness, which are of the utmost service in
the guidance of subsequent behaviour. The two-days-old chick, with
the aid of this instinctive co-ordination, performs well a number of
actions, which, had she to consciously learn them all, would probably
be still but half mastered when she was a skinny old hen.
Our whole treatment of instinctive behaviour has been based on the
assumption, already to some extent justified, that experience is
not inherited. If it be hereditary, how comes it that chicks show
no recognition of still water, which must have been familiar to the
experience of generation after generation of birds? How comes it that
they do not even seem to recognize their natural parent and protector,
the hen? Two chicks ten days old were taken to the yard whence were
derived the eggs from which they were hatched, and were placed about
two yards from a hen which was clucking to her brood. They were not in
a frightened condition, for they stood on my hand and ate grain from
it, scratching at the palm. But of the clucking of the hen they took
no notice whatever. The same results were obtained with other chicks
thirteen days old. Was this due, as Spalding suggested, to loss of
the instinctive response which was perhaps present at an earlier age?
Seemingly not. For a chick was taken at the age of two and a half days
to its own mother, which had three chicks. These followed her about,
and ran at once to her when she clucked and pecked on the ground. The
little stranger, however, took no notice, nor did he show any tendency
either to go to the hen or to follow the three chicks, having been
purposely brought up alone. When the hen took her little brood under
her wing, the stranger was placed close to her. She clucked, and seemed
anxious to entice and welcome the little fellow, seizing an oat-husk
and dropping it before him; but he remained indifferent, walking away
and standing in the sunshine. After about forty minutes he seemed more
inclined to go with the other chicks, but still ignored the existence
of the hen. The natural instinctive tendency seems to be from the first
to nestle under anything; and there is the hen provided by nature for
the purpose. By experience the chicks grow accustomed to her fussy
ways, as they grow accustomed to the ways of such a foster-parent
as the writer of these pages. Still, though there is, apparently,
no instinctive knowledge of the hen as their natural protector, and
though I have seen no observable response to the clucking sound, this
must not be taken as necessarily implying that there is no instinctive
response to any of her modes of behaviour. There is such a response
to her pecking on the ground; there is probably such a response to
her danger-note; and there may be many other such instinctive modes
of behaviour related to her actions. How far they extend can only be
ascertained by patient observation; and such responsive behaviour need
not imply any instinctive knowledge begotten of inherited experience.
We may now summarize some of the general conclusions which may be drawn
from observations of instinctive behaviour in young birds.
1. That which is inherited is essentially a motor response or train
of such responses. Mr. Herbert Spencer’s description of instinct as
compound reflex action is thus justified.
2. These often show very accurate and nicely-adjusted hereditary
co-ordinations.
3. They are evoked by stimuli, the general type of which is fairly
definite, and may in some cases be in response to particular objects.
4. They are also generally shown under conditions which lead us to
infer the presence of an internal factor, emotional or other.
5. There does not seem to be any evidence of inherited knowledge or
experience.
IV.--THE CONSCIOUS ASPECT OF INSTINCTIVE BEHAVIOUR
In our definition of instinctive behaviour all positive reference to
the presence of conscious states was omitted. By some writers, however,
the fact that it is accompanied by consciousness is regarded as a
distinguishing feature of instinct. Romanes introduced his definition
with the words:[38] “Instinct is reflex action into which there is
imported the element of consciousness.” And he emphasized the conscious
aspect when he said: “The term comprises all those _faculties of mind_
which are concerned with conscious and adaptive action, antecedent to
individual experience.” Professor Wundt also lays some stress on the
conscious accompaniments of instinctive activities which, he says,[39]
“differ from the reflexes proper in this, that they are accompanied
by emotions in the mind, and that their performance is regulated by
these emotions.” The definitions of other writers express or imply the
presence of consciousness in differing modes and degrees, culminating
in the hypothesis of inherited knowledge. Douglas Spalding, for
example, said[40] that “animals can forget the instinctive knowledge
which they never learned!”
Now, the exclusion from our definition of direct reference to the
conscious aspect must not be taken to imply that instinctive behaviour
is a mere matter of unconscious automatism; nor even that it is
unprofitable to discuss how much consciousness there may be, of what
sort, and how distributed. All that it does imply is, that the amount,
nature, and distribution of consciousness cannot well be introduced
into a definition the object of which is to help us to distinguish
certain observable types of behaviour from others. In a word, the
definition given is biological and objective, and is to be accepted
or rejected without prejudice to such psychological considerations as
those upon which we have now briefly to enter.
The first thing we have to decide is how much we are to include,
from the psychological standpoint, under instinct. For we may take
either a broader or a narrower view of the matter; and which of these
we adopt will make much difference in our conclusions. Let us first
deal with the narrower. We have said above that what is hereditary in
instinctive behaviour is the co-ordination. Now, such co-ordination of
movements into a finished and appropriate act is due to a nicely graded
distribution of efferent nerve-waves to the several muscles concerned,
so that these muscles may be caused to contract in due order, and each
to just the right extent. But efferent nerve-waves as such, and their
mode of distribution by the nerve-centres, are in all probability
unconscious, while the contraction of the muscles is a purely organic
matter. If, therefore, we narrow our conception of instinct so as to
include only the co-ordinated act by itself, excluding all reference
both to the stimuli which are its antecedents, and to the effects in
consciousness which its performance may produce; and if the data for
consciousness are in all cases supplied through afferent channels;
then there seems to be no escape from the conclusion that instinctive
behaviour as such may be, and probably is, altogether outside the
individual consciousness. It should be noted, however, that on this
view only the instinctive co-ordination in itself can be fairly
regarded as independent of the stream of experience.
Now, in the first place it is convenient so far to broaden our
conception as to include under the head of instinctive behaviour,
in its conscious aspect, not only the co-ordinated act but the data
which its performance affords to consciousness. It may indeed seem
that we are here trying to draw a distinction where no real difference
exists. The physiological distinction is, however, not only clear and
undeniable, but quite easily understood. For the sake of illustration
let us take the case of an intentional action, such as glancing up from
the words we are reading to the clock. Efferent waves course along
several motor nerves to the six muscles by which each eye is moved,
and to the muscles of accommodation within the eye. These muscles
are called into duly co-ordinated activity, by which our vision is
focussed upon the clock-face. This is one part of the physiological
procedure--that by which the intended result is attained. But there
is a second part readily distinguishable from the former. As the
eyes move, afferent messages course inwards from the muscles or the
eye-sockets and their neighbourhood; and it is these incoming waves
which afford data to consciousness, telling us that the movements are
in progress or have been effected. The nerves involved in the latter
part are quite different from those concerned in the former part, and
they proceed to areas of the brain differently situated from those
whence the efferent waves issued. Thus it is in all cases of movement;
the efferent nerves call the muscles into play; the afferent nerves
bring information that the movements are carried out. It is through the
latter that data are unquestionably afforded to consciousness.
But in the case of any complex action--and, as we have seen,
instinctive behaviour is often remarkably complex--the information
that the action has begun comes in before the behaviour is completed.
Practically we may say that any given stage of performance and the
consciousness it evokes are simultaneous; for though in strictness
the one lags just a little behind the other, yet they are so nearly
coincident in time that we may disregard the interval between them.
Such being the case, therefore, we may fairly regard the felt
performance of the instinctive act as capable of introducing important
elements into the conscious situation.
But not only does instinctive behaviour thus introduce important
elements into the conscious situation, it is also called forth by
stimuli which themselves afford not less important elements. To exclude
these from any consideration of instinct, in its conscious aspect,
would render the treatment of the problem so incomplete as to be wholly
unsatisfactory from a psychological point of view. Can we believe that
when the moor-hen dived, as it never had dived before, at the sight
of the rough-haired pup, the vivid experience of that strange and
disquieting intruder did not enter into, and form a prominent feature
in, the conscious situation? If we are to consider the conscious aspect
at all, we must try and grasp the situation as a whole. And on these
grounds we may yet further broaden our conception so as to include,
from the psychological point of view, not only the behaviour itself,
and its effects in consciousness, but also the stimulating conditions
under which it is called into play. If, then, we accept this position,
and agree to use the term “instinct” for our present purpose in a
comprehensive sense, we may now proceed to consider very briefly the
nature of the elements which enter into the instinctive situation.
First, there are the external stimuli affecting one or more of the
sense organs, and thus evoking consciousness; and secondly, there are
internal factors, having their source in the condition of the body, or
its parts and organs. It is convenient to take these two together, so
that we may see what relationship they bear to each other. Both seem to
be present, and to co-operate in a great number of instinctive acts. In
the behaviour connected with feeding, for example, an internal element
of hunger co-operates with the external presentation of the appropriate
food or prey. So, too, with the instincts concerned in the propagation
of the race. Looking at the matter generally, we may regard the
internal factors of the kind with which we are now dealing, as giving
rise to a want or need, passing in some cases into a state of craving.
In themselves such conscious states are in their inception exceedingly
indefinite; for a want can only be rendered definite in experience by
its appropriate satisfaction. In many cases of instinctive behaviour
the indefinite want and the particular and duly related stimulus seem
to lead, without prevision and by a blind impulse, to the performance
of those acts which will afford the unforeseen satisfaction. And when
once this satisfaction has been attained, subsequent wants or needs of
like character will no longer be indefinite; nor will future behaviour
of the same kind be thereafter wholly instinctive, for it can never
again be prior to, or independent of, experience.
Granted, however, that a felt need of some kind, indefinite at
first but none the less real, is present in many cases as a spur to
instinctive behaviour; is it in all cases a necessary factor? May we
say that this distinguishes instinctive from merely reflex action? The
question is, from the nature of the case, exceedingly difficult to
answer. But without going so far as to say that reflex action may be
unerringly distinguished from instinctive behaviour by the absence of
any such internal factors, we may perhaps, at any rate, go so far as
to give provisional acceptance to the view that in instinct these wants
and felt needs enter into the conscious situation in a manner and to
a degree that are so far distinctive--which seems to be the position
adopted by Professor Wundt.
There is, however, a further relation between the external stimulus and
these internal factors which is presumably of no little importance.
The stimulus intensifies the want, or may in some cases call it into
existence. Just as a whiff from the kitchen may lead us to realize
that we need the satisfaction that will erelong be presented at table,
so may the sight of his mate in the spring evoke in the breast of
the yearling sparrow a need, having its source in morphological and
physiological changes, that spurs him on to the courtship that shall
lead to its due satisfaction. Popular attention has, indeed, been so
naturally drawn to the internal needs or wants with which we are now
dealing, as to give them an almost exclusive monopoly of the term
“instinct,” which thus often comes to be regarded as a connecting link
between the stimulus and the act. The sight of a mouse, for example, is
said to call forth the instinct of the cat, which is satisfied by her
pouncing upon it. And so it comes about that, while the biologist fixes
upon the instinctive act as the essential feature, the psychologist
is apt to regard the impulse[41] which prompts to action as the more
central and characteristic element. We are here endeavouring to combine
both these points of view.
To come to closer quarters with the relationship which holds good
between the external and internal elements, it appears that, when the
stimulus evokes or intensifies the want or need, this is probably
effected by efferent waves which call the organs or parts into tonic
action, of which the animal becomes conscious through the afferent
messages which come in from them to the sensory centres; in much the
same way as the whiff from the kitchen takes effect on the salivary
and other glands, and throws the organs of digestion into a felt
preparedness for the fulfilment of their functions. But it may have
other and more indirect consequences. When the moor-hen dived to escape
from the obtrusive puppy, his heart-beat was probably affected; he
had, perhaps, an uncomfortable sinking in his gizzard; his breathing
was short and laboured; and he experienced creepy sensations in the
skin and around the feather-roots. Such we may suppose were the
accompaniments or sources of the emotional state of fear or alarm. And
they presumably entered with no little vividness into the conscious
situation at the moment of instinctive action. In all those cases in
which the behaviour is associated with such an emotional state as anger
or fear, the external stimulus seems to produce widely-spread effects
on the glands, respiratory organs, heart and blood-vessels, skin and
other parts, as well as the more direct response in productive action.
And all this must enter into the conscious situation, contributing
largely, as we shall hereafter see, to the emotions in their
instinctive origin.
Enough has now been said to indicate with sufficient clearness the
kind of co-operation and mutual relationship which subsists between
the external and the internal factors in the conscious situation which
leads to instinctive behaviour. We have seen that, not improbably, some
organic prompting is always present in greater or less degree. But the
question still remains whether anything like a definite and particular
external stimulus is in all cases a necessary factor.
When the predaceous larva of the water-beetle, _Dytiscus_, ceases to
feed, and, creeping into the moist earth near the pond’s edge, makes
a hollow cell in which to enter upon its pupal sleep, there does not
seem to be any well-defined stimulus from the outer world which can be
said to initiate the behaviour of whose purport the larva can have no
idea. Some inner need seems to impel the creature to this necessary
but as yet unknown course of action; and this appears to constitute,
if not the sole, at least the preponderant element in the conscious
situation. In healthy young birds and other animals there is after the
rest of sleep a certain exhilaration and exuberance of spirits which
seemingly leads to characteristic action; dancing, flapping of the
wings, running hither and thither in short quick spurts, and so forth.
No doubt in such cases external stimuli are present, and contribute
in some degree to the effects produced; but they do not seem to be
particularized so that one can say that just this or that well-defined
stimulus is necessary to give rise to the observed behaviour. In the
case of migration, too, an internal factor--the nature of which we do
not know--is probably as strong as if not stronger than any influence
from without. While, therefore, we may say that some external factors
are frequently, not improbably always, contributory, we must add that
observation does not enable us in all cases to define them with any
approach to accuracy; and, further, that promptings from within seem
in some instinctive acts to be the most important elements in the
conscious situation.
It now only remains to draw attention to the fact that the effects of
the behaviour, as the animal becomes conscious of the performance of
the acts concerned, serve to complete and render definite the conscious
situation. Consciousness, however, probably receives information of the
net results of the progress of behaviour, and not of the minute and
separate details of muscular contraction. These net results, having
thus entered presentatively into the situation, are subsequently
susceptible of re-presentative recall, when the recurrence of certain
salient elements serve to reproduce the essential features of the
situation of which experience has been gained on a former occasion.
Hence, as has already been noted, it is only the _first_ performance of
an instinctive action which can be described as prior to experience.
The second time the deed is done it is done by an animal which has
had opportunity of gaining experience on the foregoing occasion. And
then it may be done with a difference, with some acquired modification
of performance. By the repetition of the slightly modified behaviour
the effects of habit are introduced, and thus acquired peculiarities
of action are established as individual traits. We must not forget
that, in a large number of cases, so-called instinctive behaviour, as
presented to observation, has lost through modified repetition its
original purity of type. The acts we see are often the joint products
of heredity and individual acquisition, the inherited co-ordination
having been supplemented or otherwise altered through experience.
Even in the case of the very first exhibition of such a deferred
instinct as the moor-hen’s dive, although that organized sequence
of acts which constituted the behaviour as a whole had never before
occurred, although there was no gradual learning how to dip beneath
the surface, and to swim under water, still many of the constituent
acts had been often repeated; experience had already been gained of
much of the detail then for the first time combined in an instinctive
sequence. So that if we distinguish between instinct as congenital and
habit as acquired, we must not lose sight of the fact that there is
continual interaction, in a great number of cases, between instinct
and habit, and that the first performance of a deferred instinct may
be carried out in close and inextricable association with the habits
which, at the period of life in question, have already been acquired.
Instinct supplies an outline sketch of behaviour, to which experience
adds colour and shading. Which predominates in the finished picture
depends on the status of the animal. In the lower and less intelligent
types the outline stands out clearly, there being but little shading to
divert our attention from the clear firm lines inscribed by heredity;
but in the higher and more intelligent animals, the deft pencil of
experience has added so much detail and has interwoven with the fainter
outline so many new and skilfully introduced touches, that the original
sketch is scarcely distinguishable unless we have carefully watched
from the beginning the gradual development of the picture.
V.--THE EVOLUTION OF INSTINCTIVE BEHAVIOUR
It may be assumed that the fact of evolution is generally admitted.
The question of its method is, however, still open to discussion. It
is possible that, as some biologists contend, there is an inherent
tendency in organic beings to evolve in certain definite directions
independently of their relation to the environment. But it is scarcely
probable that instinctive behaviour is mainly due to any such inherent
tendency--of the nature of which in any case we know but little.
Setting this on one side, therefore, we have two hypotheses: first,
that instincts are the result of natural selection; secondly, that they
are due to the inheritance of acquired habits. These two views we will
now proceed to consider.
We have seen that Professor Wundt distinguishes two classes of
instinctive acts: first, those which are _acquired_ or have become
wholly or partly mechanized in the course of individual life; secondly,
those which are _connate_ or have been mechanized in the course of
generic evolution. “The laws of practice,” he says,[42] “suffice for
the explanation of the acquired instincts. The occurrence of connate
instincts renders a subsidiary hypothesis necessary. We must suppose
that the physical changes which the nervous elements undergo can be
transmitted from father to son.... The assumption of the inheritance of
acquired dispositions or tendencies is inevitable if there is to be any
continuity of evolution at all. We may be in doubt as to the extent of
this inheritance; we cannot question the fact itself.”
Now, the application of the term “instinct,” both to acquired and to
connate behaviour, seems to prejudge the question of their genetic
connection. And since we have the well-recognized term _habits_ for
actions the performance of which becomes automatic through frequency
of repetition, we may substitute this term, or the phrase _habitual
acts_, for the “acquired instincts” of Professor Wundt. Modifying,
therefore, his statement in accordance with this usage, the fact which,
he says, we cannot question is that acquired habits are inherited as
congenital instincts. This opinion has long been held: G. H. Lewes
regarded instinctive actions as transmitted habits from which the
intelligence, through which they were originally acquired, had lapsed.
Darwin believed that such inheritance was a factor in the evolution
of instinctive behaviour. Romanes distinguished instincts due to
this mode of origin as “secondary;” reserving the term “primary” for
those attributable to natural selection, and describing those in which
both factors co-operate as “instincts of blended origin.” The late
Professor Eimer, of Tübingen, going further than either Darwin or
Romanes, reverted almost entirely to what we may term the Lamarckian
interpretation. “I describe as automatic actions,” he says,[43]
“those which, originally performed consciously and voluntarily, in
consequence of frequent practice come to be performed unconsciously and
involuntarily.... Such acquired automatic actions can be inherited.
Instinct is inherited faculty, especially is inherited habit.” In his
discussion of the subject Eimer makes no express allusion to primary
instincts; but he attributes to lapsed intelligence some of those
which were classed by Romanes as primary, and his tendency is to
refer all instincts to the same source. “Every bird,” he says, “must,
from the first time it hatches its eggs, draw the conclusion that
young will also be produced from the eggs which it lays afterwards,
and this experience must have been inherited as instinct.” Why, in
the first instance, it must draw the conclusion from observation if
it inherit instinctive knowledge, is not made clear. But our present
purpose is to indicate, not to criticize, Eimer’s position. He claims
that “the original progenitors of the cuckoo, when they began to
lay their eggs in other nests, acted by reflection and design.” Of
the behaviour of mason wasps and their allies, which provide their
young with paralyzed but living prey, he exclaims, “What a wonderful
contrivance! What calculation on the part of the animal must have been
necessary to discover it!” Of the instincts of neuter bees he remarks,
“Selection cannot here have had much influence, since the workers do
not reproduce. In order to make these favourable conditions constant,
insight and reflection on the part of the animals, and the inheritance
of these faculties were necessary.” And he concludes, “Thus, according
to the preceding considerations, automatic action may be described as
habitual voluntary action; instinct, as inherited habitual voluntary
action, or the capacity for such action.”
Turning now to the opposite end of the scale of opinion, we find
that Professor Weismann, commenting on the supposed inheritance
of acquired habit, says,[44] “I believe that this is an entirely
erroneous view, and I hold that all instinct is entirely due to the
operation of natural selection, and has its foundation, not upon
inherited experiences, but upon variation of the germ.” Ziegler and
Groos in Germany, Whitman and Baldwin in America, Poulton and Wallace
in England, either deny the existence of secondary instincts, due
to the inheritance of acquired habits, or question the sufficiency
of the evidence adduced in support of such transmission. In their
explanation of the manner in which that inherited co-ordination,
which is biologically the central fact in instinctive behaviour, has
been evolved they rely mainly or entirely on the principle of natural
selection.
What, then, were the facts which appeared to Romanes sufficient to
justify a belief in the existence of a class of instincts dependent
on inherited habit for their origin? He tells us that he only gives a
few examples “amongst almost any number” that he could quote. It is
certainly unfortunate that, out of more than one hundred and fifty
pages devoted to instinct in his work on “Mental Evolution in Animals,”
only three[45] are assigned to secondary instincts; or six, if we
include one dealing with inherited peculiarities of hand-writing in
man, and two showing the force of heredity in the domain of instinct,
“whether of the primary or secondary class.” It is true that many pages
are devoted to instincts of blended origin, but the co-operation of
the Lamarckian factor is here rather assumed than proved. We must,
however, be content to take the few examples that are actually given.
They are four in number. First, that ponies in Norway are used without
bridles, and are trained to obey the voice; and that, as a consequence,
a race-peculiarity has been established, for Andrew Knight says that
it is impossible to give them what is called “a mouth.” No details are
given, and Romanes does not further discuss the evidence. Secondly,
Mr. Lawson Tait had a cat which was taught to beg for food like a
terrier. All her kittens adopted the same habit under circumstances
which precluded the possibility of imitation. Supposing the facts to
be correctly reported, and granting that the owners of the kittens,
presumably aware of the maternal propensity, did not take some pains to
teach the offspring of such a parent to beg (and this does not present
much difficulty), one can hardly found a scientific conclusion on so
slight an anecdotal basis. Thirdly, instinctive fear is said to be an
inherited acquisition; which, fourthly, is lost by disuse. But, as
we have already seen, modern investigation has placed this matter of
so-called hereditary fear of natural enemies on a different footing.
Pheasants, partridges, moor-hens, and wild duck show no fear of a quiet
dog. If approached gently, in the absence of their parents, callow
wild birds in their nest exhibit little alarm at the slow and gentle
approach of man. Mr. Hudson’s opinion has already been quoted, but
will bear repetition; it is, “that fear of particular enemies is in
nearly all cases the result of experience.” And there is no evidence to
show that, in those cases in which it is truly instinctive and not the
result of experience, the instinctive behaviour is necessarily due to
inherited habit and not to natural selection.
It cannot be said that the evidence for the supposed mode of origin
of secondary instincts is sufficiently varied and cogent to carry
conviction. On the other hand, there does seem some evidence which
points to a different conclusion. When instinctive behaviour follows
on a sensory impression, not only is the co-ordination hereditary,
but there is an inherited linkage of stimulus and response. Thus in
the solitary wasps the sight of the natural prey is followed by the
appropriate modes of attack. The _Meloë_ larva springs upon anything
hairy. In chicks the sight of a small object at a certain distance
initiates the act of pecking. In moor-hens and ducklings the stimulus
of water produces the movements concerned in swimming. And so, too,
in many other examples of instinctive behaviour, we infer from the
observed facts that stimulus and response have an organic connection
founded on hereditary links in the nervous system. Now, if such
connection were due to inherited habit, we should expect them to be
established wherever the experience to which they are related has
been constant through many generations. How comes it, then, that the
chick does not instinctively respond by appropriate behaviour to the
sight of water? How comes it that young birds do not instinctively
avoid bees, and wasps, and nauseous caterpillars? If the effects of
ancestral experience be hereditary, one would surely expect that in
these cases the connection between stimulus and response--a connection
which passes into acquired habit--would have become congenital; that
the habitual behaviour would have long ago become instinctive. But this
does not appear to be the case. And with regard to disuse causing the
loss of instinct, how comes it that young chicks swim with well-ordered
leg-movements, though swimming is not an act that is habitually
performed by the members of their race?
What, then, has the alternative hypothesis of natural selection to
advance in explanation of these facts? On this hypothesis instinctive
acts have biological value in such degree that they have become
congenital through the preservation of adaptive variations. But if this
be so, why does not the chick respond instinctively to the sight of
that which is so essential to its existence as water to drink? In reply
to this question it may be suggested that, under natural conditions,
the hen teaches all her chickens to peck at the water, and thus shields
them from the eliminating influence which gives rise to natural
selection, in the absence of which the habit of drinking in response
to the sight of water, though acquired by each succeeding generation
of birds, has not become instinctive and congenital. Or, to put the
matter from a slightly different point of view, the maternal instincts
of the hen protect her chicks from any elimination in this respect; and
in the absence of such elimination the habit has not been inherited as
instinct. But though the hen can lead her young to peck at the water,
she cannot teach them how to perform the complex movements of the
mouth, throat, and head in actual drinking. In this matter, therefore,
her own instinctive procedure does not shield them from the incidence
of that elimination which leads to survival under natural selection.
Those chicks would be eliminated which, on pecking the water, failed to
respond to the stimulus by the complex behaviour involved in drinking,
leaving those to survive in which the response had been congenitally
established. Thus it would seem that, when natural selection is
excluded, the habit has not become congenitally linked with a visual
stimulus; but when natural selection is in operation, the response has
been thus linked with the stimulus of water in the bill. Whence we may
infer that the co-operation of natural selection is an essential factor
in the evolution of instinctive behaviour.
There are, however, cases of instinctive behaviour which may seem too
trivial and unimportant to be subject to the sway of natural selection.
There are numberless little idiosyncracies of behaviour which seem to
be truly instinctive, which are readily recognizable as distinctive
traits, but which can hardly be regarded as of sufficient biological
value to determine whether the creatures in which they are developed
should survive or be eliminated in the struggle for existence. In many
cases, however, these serve rather to distinguish the detailed manner
of behaviour than its biological end or purpose. In different species
natural selection may determine the survival of those whose instinctive
behaviour meets a biological need. The relatively unimportant details,
differing slightly in each species, are mere adjuncts; and since
natural selection deals with each species or inter-generating group
separately, the essential behaviour may in each case carry with it
the associated differences of manner. We must remember, too, that, as
in the matter of structure so in that of behaviour, it is the animal
as a whole that is selected for survival; and so long as the whole
is adapted to the circumstances of life, the associated differences
of form or manner may share in, without doing much to determine,
survival. In any case these little instinctive traits, if they are so
trivial as to seem of small value from the biological point of view,
appear to be too unimportant to have been intelligently acquired as
habits.
Let us now consider one or two cases of instinctive behaviour which
would fall under Romanes’s category of instincts of blended origin
partly due to natural selection, partly to the inheritance of acquired
habit. It is the custom of the house martin to build beneath the eaves.
Forsaking the ancestral rocky haunts, it has been led to utilize
the houses that man has built. This has all the appearance of being
due to an intelligent modification of the ancestral instinct; but
how far the modification has become through heredity a congenital
variation, we do not know. The intelligence which is said to have
enabled the martin of the past to adopt this method of nidification is
still operative. The nestlings brought up under the eaves would have
opportunities for acquiring experience which might lead them to build
under similar circumstances. Nest and eaves would be associated in
the conscious situation. Nor would the effects of natural selection
be necessarily excluded. One may suppose that in the open country,
far from rock-shelters, those martins in which there was a congenital
tendency to build in house-shelters would bring up their broods and
transmit this tendency; while those in which it was absent would either
go elsewhere or fail to bring up broods at all. In the absence of
fuller knowledge as to the truly instinctive nature of the behaviour,
and as to its mode of genesis, we are in large degree at the mercy
of conjecture. But in any case the incidence of elimination is not
necessarily excluded, and there are, therefore, no grounds for denying
that natural selection has been a co-operating factor in the evolution
of the instinctive behaviour, if such it be.
It is well known that the lapwing will apparently simulate the
actions of a wounded bird, with the object, as it seems, of drawing
intruders away from her nest. And such tactics are not restricted
to this bird, nor even to one or two species. They are common,
no doubt with diversities of detail, to such different birds as
grouse, pigeons, plovers, rails, avocets, ducks, pipits, buntings,
and warblers. Granting that the behaviour is truly instinctive, it
forms a very pretty subject for transmissionists and their critics to
quarrel over. “If we seek, as an example,” the transmissionist may
exclaim, “an instinct which bears the marks of its intelligent, and
therefore acquired origin, this of feigning wounded provides all that
we can possibly demand.” “What mode of instinctive behaviour,” the
selectionist may ask, “can be adduced which is more obviously useful
to the species? Is not this just the kind of procedure which natural
selection, if it be a factor at all, must fix upon and perpetuate
through the elimination of failures? Those birds which, through
congenital variation of behaviour, acted in this way would certainly
enable their offspring to escape destruction by enemies, and these
would survive to perpetuate the instinct.”
Let us expand the transmissionist position a little further. An
extremist, of the type presented by Eimer, would perhaps urge that the
lapwing reasons thus: “If I pretend to be wounded, trail my wing, and
flutter along the ground, instead of flying off, I shall draw upon
myself the intruder’s attention, and lead him to suppose that I shall
be easily caught; and if I thus entice him away, my little ones will be
saved, and my end gained.” Thus, it may be said, might the bird argue,
and then give practical effect to its reasoning. But are we not here
attributing to the lapwing powers of ratiocination beyond the capacity
of the most intelligent of birds? Are we not assuming a histrionic
power, and a realization of the effects on others of its display, which
many a human actor might well covet?
“But may not the bird,” it may be urged in reply, “have found by
experience, without any elaborate process of abstract reasoning, that
the trick is effectual?” In any case it would be experience perilously
acquired. Granting that the bird has the wit to try the trick, a
little over-acting, a little too much lameness of wing, and she is
herself seized and killed; a little under-acting, and the trick
fails--her brood is found and destroyed. Does it not seem probable
that such experience would be dearly bought, that failure would mean
either death to the parent or death to the offspring? And is it not
clear that natural selection is thus introduced in any case? And may
not the selectionist pertinently ask: “If natural selection is thus
introduced as a factor, why halt midway between two hypotheses? Why
not take the further step--one by which all the difficulties attending
the intelligent acquisition and the biological transmission are alike
avoided--of allowing that natural selection exercises, throughout, its
influence on congenital variations, and not on acquired modifications
of behaviour?”
There is, however, a way in which, when natural selection is operative,
intelligence may serve to foster congenital variations of the required
nature and direction. We must remember that acquired habits on the one
hand, and congenital variations of instinctive behaviour on the other
hand, are both working, in their different spheres, towards the same
end, that of adjustment to the conditions of life. If, then, acquired
accommodation and congenital adaptation reach this end by different
methods, survival may be best secured by their co-operation. And the
more thorough-going the co-operation the better the chance of survival.
There would be a distinct advantage in the struggle for existence when
inherited tendencies of independent origin coincided in direction with
acquired modifications of behaviour; a distinct disadvantage when such
inherited tendencies were of such a character as to thwart or divert
the action of intelligence. Thus any hereditary variations which
coincide in direction with modifications of behaviour due to acquired
habit would be favoured and fostered; while such variations as occurred
on other and divergent lines would tend to be weeded out. Professor
Mark Baldwin,[46] who has independently suggested such relation
between modification and variation, has applied to the process the
term “Organic Selection;” but it may also be described as the natural
selection of coincident variations.
It may be urged, therefore, that if natural selection be accepted as
a potent factor in organic evolution, and unless good cases can be
adduced in which natural selection can play no part and yet habit has
become instinctive, we may adopt some such view as the foregoing.
While still believing that there is some connection between habit and
instinct, we may regard the connection as indirect and permissive
rather than direct and transmissive. We may look upon some habits as
the acquired modifications which foster those variations which are
coincident in direction, and which go to the making of instinct.
The net result of a study of instinctive behaviour is to lead us to
the conclusion that its evolution runs parallel with the evolution
of animal structure. This is perhaps best seen in the case of those
insects in which typical instinctive acts are performed by larvæ of
wholly different form and structure, though they are stages in the
development of the same species. This is exemplified in the cases
of _Sitaris_, _Argyromœba_, and _Leucopsis_ which have been briefly
described. It is probable that in all cases of instinctive action
natural selection has been a co-operating factor. Without going so far
as to assert with Professor Weismann the “all-sufficiency of natural
selection,” we may echo the words of Professor Groos,[47] and say:
“Nevertheless, we know no principle except that of selection, and
we must go as far as that will take us. Absolute knowledge of such
phenomena is unattainable.” And in this conclusion we have the support
of Dr. Peckham, who says,[48] “We have found them [the instinctive
acts of solitary wasps] in all stages of their development, and are
convinced that they have passed through many degrees from the simple
to the complex, by the action of natural selection. Indeed, we find in
them beautiful examples of the survival of the fittest.”