succeed, he was taken out, but _not fed_. If, after a sufficient
number of trials, he failed to get out, the case was recorded as one
of complete failure. Enough different sorts of methods of escape
were tried to make it fairly sure that association in general, not
association of a particular sort of impulse, was being studied.
Enough animals were taken with each box or pen to make it sure that
the results were not due to individual peculiarities. None of the
animals used had any previous acquaintance with any of the mechanical
contrivances by which the doors were opened. So far as possible the
animals were kept in a uniform state of hunger, which was practically
utter hunger.”
[Illustration: FIG 22.--Cage used in Professor Thorndike’s
experiments.]
To Dr. Thorndike’s monograph we must refer those who desire detailed
information as to apparatus and procedure. It must here suffice to
state that the box-cages employed were rudely constructed of wooden
laths, and formed cramped prisons about twenty inches long by fifteen
broad and twelve high. Nine contained such simple mechanisms as Dr.
Thorndike describes in the passage above quoted. When a loop or cord
was pulled, a button turned, or a lever depressed, the door fell open.
In another, pressure on the door as well as depression of a thumb-latch
was required. In one cage two simple acts on the part of the kitten
were necessary, pulling a cord and pushing aside a piece of board; and
in yet others three acts were requisite. In those boxes from which
escape was more difficult a few of the cats failed to get out. The
times occupied in thoroughly learning the trick of the box by those
who were successful are plotted in a series of curves, the essential
feature of which is the graphic expression of a gradual diminution
in the time interval between imprisonment and escape in successive
trials. This is shown in Fig. 23, which is constructed from some of Dr.
Thorndike’s data. In some cases the cats were set free from a box when
they (1) licked themselves or (2) scratched themselves.
[Illustration: FIG. 23.--Diagram showing times taken by a kitten to
escape from the cage in twenty-four successive experiments.]
Dr. Thorndike comments on the results of his experiments as follows:--
“When put into the box the cat would show evident signs of discomfort
and of an impulse to escape from confinement. It tries to squeeze
through any opening; it claws and bites at the bars or wire; it
thrusts its paws out through any opening, and claws at everything
it reaches; it continues its efforts when it strikes anything loose
and shaky: it may claw at things within the box. It does not pay
very much attention to the food outside, but seems simply to strive
instinctively to escape from confinement. The vigour with which it
struggles is extraordinary. For eight or ten minutes it will claw,
and bite, and squeeze incessantly.... The cat that is clawing all
over the box in her impulsive struggle will probably claw the string,
or loop, or button so as to open the door. And gradually all the
other non-successful impulses will be stamped out, and the particular
impulse leading to the successful act will be stamped in by the
resulting pleasure, until, after many trials, the cat will, when put
in the box, immediately claw the button or loop in a definite way....
Starting, then, with its store of instinctive impulses, the cat hits
upon the successful movement, and gradually associates it with the
sense-impression of the interior of the box until the connection is
perfect, so that it performs the act as soon as confronted with
the sense-impression.... Previous experience makes a difference
in the quickness with which the cat forms the associations. After
getting out of six or eight boxes by different sorts of acts, the
cat’s general tendency to claw at loose objects within the box is
strengthened and its tendency to squeeze through holes and bite
bars is weakened; accordingly it will learn associations along the
general line of the old more quickly. Associations between licking
or scratching and escape are similarly established, and there was
a noticeable tendency to diminish the act until it becomes a mere
vestige of a lick or scratch. After the cat gets so that it performs
the act soon after being put in, it begins to do it less and less
vigorously. The licking degenerates into a mere quick turn of the
head with one or two motions up and down with tongue extended.
Instead of a hearty scratch, the cat waves its paw up and down
rapidly for an instant.”
Such experiments carried out on a different method give results in line
with my own. The conditions are, however, somewhat unnatural, which
I regard as in some respects a disadvantage. But we need experiments
on different methods--the more the better,--and if the results they
furnish are in accord, their correctness will be rendered the more
probable. It is to be hoped that Dr. Thorndike will devise further
experiments in which (1) the conditions shall be somewhat less strained
and straitened, while the subjects are in a more normal state of
equanimity (cannot “utter hunger” be avoided?), and (2) there shall
be more opportunity for the exercise of rational judgment, supposing
the faculty to exist. To establish the absence of foresight in the
procedure of the cats, it is surely necessary so to arrange matters
that the connections are clearly open--nay, even obvious--to the eye of
reason. It appears that this consideration has not weighed sufficiently
with Dr. Thorndike.
A series of experiments were made to ascertain whether instruction
(in the form of putting the animal through the procedure requisite
for a given act) was in any degree helpful. The conclusion is that
such instruction has no influence. Those who have had experience in
teaching animals to perform tricks will probably agree here--though
some trainers give expression to a different opinion. It is, however,
essential to distinguish carefully between showing an animal how a
trick is done, and either stimulating its attention or furnishing
accessory guidance (such as the occasional taps of the trainer’s whip
when he wants a performing horse to kneel), or affording suitable
conditions the results of which temporarily enter into the association
complex. If the latter be eliminated the practice of trainers, I
believe, bears out the general result of the experiments. Dr. Thorndike
never succeeded in getting an animal to change its way of doing a thing
for his. Nor was I, after repeated trials, able to modify the way in
which my dog lifted the latch of the gate. He did it with the back
of his head. I could not get him to do it (more gracefully) with his
muzzle.
It may be said that the remarkable feats of performing animals imply
the existence of faculties of a higher order than Dr. Thorndike and
I are prepared to admit on the basis of our experiments. Mr. P. G.
Hamerton many years ago described[64] how, in his own house, a cleverly
trained dog would fetch in their right order the letters which spelt
the English or German equivalents of common French words, and do other
wonderful things. But the owner of the dog (M. du Rouil) admitted that
there was a means of rapport between them which he was not prepared to
divulge. It is just because the trainer has to lead up to and utilize
chance experiences that such prolonged patience and care are required.
The animal is but the instrument on which his clever trainer plays;
an instrument of wonderful intelligence, but lacking in the higher
rational faculty. The organized scheme is the master’s, not that of his
willing slave. A rational being might not do more wonderful things; but
he would learn them more rapidly and by a less wearisome method. As it
is, the clever performing dog originates little or nothing, and repeats
again and again the same stereotyped behaviour, which--if one witnesses
the performance often--touches one with a profound sense of its lack of
rational spontaneity.
As at present advised, therefore, I see no reason for withdrawing
from the position provisionally taken up. The utilization of chance
experience, without the framing and application of an organized
scheme of knowledge, appears to be the predominant method of animal
intelligence.
On this view, then, we may see in instinctive behaviour, and the
multifarious automatic acts of animals, a means of providing
experience of the right kind and on profitable lines. We may see in
the play-instincts of the young a training ground for the more serious
business of animal life--a theme developed by Professor Groos. We
may see in the imitative tendency--the innate proclivity to follow
a lead blindly and at first unintelligently--a further means of
providing those useful items of experience which intelligence finds so
serviceable. And we may see in the intelligence which can profit by
chance occurrences that arise in these several ways all that suffices
for the simple needs of animal existence.
With some differences of opinion Dr. Thorndike and I have much in
common in the conclusions to which we have been independently led
as to the method and limits of animal intelligence. We seem to be
in essential agreement in the belief that the method of animal
intelligence is to profit by chance experience without rational
foresight, and that unless such experience be individually acquired,
the data essential for intelligent progress are absent. While in our
attempts to realize the general nature of animal consciousness there
is a close similarity of treatment. In my “Introduction to Comparative
Psychology” a good deal of space is devoted to an analysis of the
psychology of skill “in order that we may infer what takes place in
the minds of animals;” and I said:--“When I am playing a hard game of
tennis, or when I am sailing a yacht close to the wind in a choppy
sea, self does not at all tend to become focal. Hence, though I am a
self-conscious being I am not always self-conscious. And presumably
when I am least self-conscious, I am nearest the condition of the
animal at the stage of mere sense experience. I am exhilarated with the
sense of pleasurable existence, my whole being tingles with sentient
life. I sense, or am aware of, my own life and consciousness, in an
unusually subtle manner. Experience is vivid and continuous. Such I
take it to be the condition of the conscious but not yet self-conscious
animal.”
I can therefore cordially endorse Dr. Thorndike’s conclusions as
expressed in the following passages:--
“One who has watched the life of a cat or dog for a month or more under
test conditions, gets, or fancies he gets, a fairly definite idea of
what the intellectual [intelligent] life of a cat or dog feels like. It
is most like what we feel when consciousness contains little thought
about anything, when we feel the sense-impressions in their first
intention, so to speak, when we feel our own body, and the impulses
we give to it. Sometimes one gets this animal consciousness while in
swimming, for example. One feels the water, the sky, the birds above,
but with no thoughts about them or memories of how they looked at other
times, or æsthetic judgments about their beauty; one feels no ideas
about what movements he will make, but feels himself make them, feels
his body throughout. Self-consciousness dies away. Social consciousness
dies away. The meanings, and values, and connections of things die
away. One feels sense-impressions, has impulses, feels the movements he
makes; that is all.”
And after an illustration from such a game as tennis, Dr. Thorndike
adds: “Finally the elements of the associations are not isolated.
No tennis-player’s stream of thought is filled with free-floating
representations of any of the tens of thousands of sense-impressions
or movements he has seen and made on the tennis-court. Yet there
is consciousness enough at the time, keen consciousness of the
sense-impressions, impulses, feelings of one’s bodily acts. So with the
animals. There is consciousness enough, but of this kind.”
It may be said that between the method of intelligence and that of
fully developed rational procedure there is a wide gap which must
have been bridged in the course of mental evolution. Unquestionably.
And in contending that the methods of the animal are predominantly
intelligent, I am far from wishing to assert dogmatically that in no
animals are there even the beginnings of a rational scheme. Indications
thereof do not indeed at present appear to have been clearly disclosed
by experiment. But the experimental development of the subject is still
in its infancy. We shall probably have to await the further results
which must be the outcome of patient and well-directed child-study.
The human child does pass in the course of his individual development
from intelligent to rational procedure. Here there is a bridge which
is crossed by every child. When we know more about the stadia of this
development we shall be in a position to apply the results obtained in
child-study in the analogous field of animal-study. Till then we must
possess our souls in patience, and base our provisional conclusions on
the results of systematic investigation, rather than on those of casual
observation and anecdote.
IV.--THE EVOLUTION OF INTELLIGENT BEHAVIOUR
No attempt can be made in this section to trace the successive stages
of the evolutionary progress of intelligence from its lower to its
higher developments. It is indeed questionable whether comparative
psychology has, as yet, accumulated a sufficient body of data to render
such a task profitable or even possible. And the lower the level of
intelligence with which we have to deal, the less reliable are the
scanty psychological data which we can obtain. To interpret the mental
processes which accompany the acts of even the higher animals is a
hard task, requiring careful psychological analysis. Still harder is
the task to infer the psychological basis of the actions of the lower
animals.
It is difficult to say where, in the hierarchy of animal progress, the
beginnings of intelligence can first be traced. In the articulated
animals, such as the insects, spiders, and crustacea, there is abundant
evidence of intelligence of a relatively high grade. But even in their
case, how hard it is to realize the nature of their experience--to
get any adequate notion of their mental processes! We are inevitably
forced to describe their psychology in the most general terms. So, too,
with forms still lower in the scale of intelligence. Many molluscs
unquestionably profit by experience. But can we clearly picture to
ourselves the nature and manner of acquisition of this experience? The
way in which limpets return to the scars on the rock which form their
homes seems to show that they have acquired a practically adequate
experience of their near surroundings. Romanes cites[65] some of the
earlier observations which have been extended by Professor Ainsworth
Davis.[66] I looked into the matter myself some years ago, at Mewps Bay
near Lulworth in Dorsetshire. The method adopted[67] was to remove the
limpets from the rock, and affix them at various distances from their
scars. This can be done without difficulty or injury to the mollusc if
one catches them as they are moving. But one must make sure that they
are just leaving or returning to their proper homes, and are not taken
in the midst of a more extended peregrination, as in that case their
special scars cannot be noted. Failure to be careful in this matter
vitiated my earlier observations, which are therefore excluded in the
following table:--
---------+------------+------------------------------------+
Number | Distance | Number returned. |
removed. | in inches. +-------------+-------------+--------+
| | In 2 tides. | In 4 tides. | Later. |
---------+------------+-------------+-------------+--------+
25 | 6 | 21 | -- | -- |
21 | 12 | 13 | 5 | -- |
21 | 18 | 10 | 6 | 2 |
36 | 24 | 1 | 1 | 3 |
---------+------------+-------------+-------------+--------+
From the nature of the rock surfaces the removal of a limpet to a
distance of two feet almost invariably involved placing them on the
further side of an angle. And though some returned over such an angle,
the majority did not.
In most cases the individuals which failed to return to their
respective scars took up new positions; and in several instances, when
they were subsequently removed to a distance of a few inches from this
new position, they returned to it. Their return to the scar was watched
in many cases, and the course was fairly, but not quite direct. One
limpet covered a distance of ten inches, over a somewhat curved course,
in a little under twenty minutes. In another case the limpet on its
return journey had to pass between two others, which necessitated the
lifting of the shell to some height so as to clear one of them. On
reaching the scar they twist and turn about so as to fit down in the
normal position which is constant. When they come up the wrong way
round they rotate pretty rapidly through the 180 degrees to get into
position. One was observed to make a short excursion from and return to
its scar under stillish water. But as a rule they seem to remain fixed
when they are submerged, moving for the most part when the tide has
just receded.
The greatest distance I have watched a limpet reach from its home was
twenty-two inches. But I have found them at a distance of three feet
from their scars--that is to say, from those to which they fitted
perfectly. This was on a large flat surface.
When they move, the tentacles are projected out beyond the shell, and
keep on touching and slightly adhering to the rock. On reaching the
scar they carefully feel round it with the tentacles. By excision
of these feelers Professor Davis was led to conclude that it is not
through their instrumentality that the limpet finds its way back to its
particular scar. But I am inclined to question these results. At any
rate, further observations and experiments are needed to settle the
point.
Snails will also return to special dark hollows or crannies in the
wall after their foraging excursions. Such behaviour in molluscs
affords evidence of something more than instinct. In popular speech,
we should say that there is memory of the locality. And in any case
it is difficult to interpret the facts without the assumption that
the animals are conscious, and that re-presentative states are
evoked through the mediation of presentative sense-impressions. But
how difficult, if not impossible, it is to form anything like a
satisfactory conception of the rudimentary mental processes of a limpet!
The most highly developed molluscs are the cephalopods. They have
long sensitive mobile arms with which they feel for and capture their
prey. “Now Schneider observed,” writes Dr. Stout,[68] “a very young
octopus seize a hermit-crab. The hermit-crab covers the shell in which
it takes up its abode with stinging zoophytes. Stung by these, the
octopus immediately recoiled and let its prey escape. Subsequently it
was observed to avoid hermit-crabs. Older animals of the same species
managed cleverly to pull the crab out of its house without being
stung.” Such cases afford evidence of profiting by experience through
the exercise of intelligence.
Darwin’s careful observations on the manner in which earthworms
drag leaves into their burrows seem to show that these annelids act
intelligently, and deal with leaves of different shapes in different
ways. The leaves of Pine trees, consisting of two needles arising
from a common base, were almost invariably drawn down by seizing this
basal point of junction; while the leaves of the Lime were, in 79
per cent. of the cases examined, drawn down by the apex; in only 4
per cent. by the base; and in the remaining 17 per cent. by seizing
some intermediate portion. On the other hand, the leaves of the
Rhododendron, in which the basal part of the blade is often narrower
than the apical part, were in 66 per cent. of the observations drawn
down by the narrower base. Triangles of paper were in the majority of
cases seized by the apex. Commenting upon his observations, carried
out with great care under experimental conditions, Darwin says,[69]
“As worms are not guided by special instincts in each particular case,
though possessing a general instinct to plug up their burrows, and as
chance is excluded, the next most probable conclusion seems to be that
they try in different ways to draw in objects, and at last succeed
in some one way;” that is to say, they profit by experience based on
the method of trial and failure. But Darwin adds that the evidence he
obtained shows “that worms do not habitually try to draw objects into
their burrows in many different ways.” And he seems to attribute to
them an almost rational power of dealing with the circumstances in the
light of general conceptions. “If worms,” he says, “are able to judge,
either before drawing or after having drawn an object close to the
mouths of their burrows, how best to drag it in, they must acquire some
notion of its general shape. This they probably acquire by touching it
in many places with the anterior extremity of their bodies, which acts
as a tactual organ. It may be well to remember how perfect the sense of
touch becomes in a man when born blind and deaf, as are worms. If worms
have the power of acquiring some notion, however rude, of the shape of
an object and of their burrows, as seems to be the case, they deserve
to be called intelligent; for they then act in nearly the same manner
as would a man under similar circumstances.”
Such power of perceiving the relation of the shape of a leaf or other
object to the form of the burrow is presumably beyond the reach of
an earthworm. It may be regarded as more probable that the earthworm
inherits an instinctive tendency to draw down objects in special
ways, and that this is subject to some modification under the play
of experience, without the formation of anything so psychologically
complex as a general notion, however rude. In any case the behaviour
of earthworms in closing their burrows seems to afford indications
of something more than instinct--of that profiting by the results of
experience which characterizes intelligent procedure. More than this we
cannot say.
Professor Whitman[70] has made some interesting observations on
the leech _Clepsine_. “Place the animal,” he says, “in a shallow,
flat-bottomed dish, and leave it for a few hours or a day, in order
to give it time to get accustomed to the place, and come to rest
on the bottom. Then, taking the utmost care not to jar the dish or
breathe upon the surface of the water, look at the _Clepsine_ through
a low magnifying lens, and see what happens when the surface of the
water is touched with the point of a needle held vertically above the
animal’s back. If the experiment is properly carried out, it will be
seen that the respiratory undulations (if such movements happen to be
going on) suddenly cease, and that the animal slightly expands its body
and hugs the glass. Wait a few moments until the animal, recovering
its normal composure, again resumes its respiratory movements. Then
let the needle descend through the water until the point rests on the
bottom of the dish at a little distance from the edge of the body.
Again the movements will cease, and the animal will hug the glass with
its body somewhat expanded. Now push the needle slowly along towards
the leech, and notice as the needle comes almost in contact with the
thin margin of the body, that the part nearest the needle begins to
retreat slowly before it. This behaviour shows a surprising keenness of
tactile sensibility, the least touch of the water with a needle-point
being felt at once.... If its back were rubbed with a brush or the
handle of a dissecting needle, in order to test its sensitiveness to
touch, the appearance would probably be that of insensibility and
indifference to the treatment. Closer examination, however, would
show that the flesh of the animal was more rigid than usual, and that
the surface was covered with numerous stiff, conical elevations, the
dermal papillæ or warts, which are so low and blunt in the normal
state of rest as to be scarcely visible. It would be seen that the
animal, although motionless, was in a state of active resistance to
attack.... _Clepsine_ has another and entirely different method of
keeping quiet. The animal rolls itself up (head first and ventral side
innermost) into a hard ball, outwardly passive, free to roll or fall
whithersoever gravity or currents of water may direct it.... If by
chance the animal has eggs, it will not desert them to escape in this
way.... This species, then, has two quite distinct and peculiar ways
of keeping quiet, and thus avoiding its enemies. If the animal has no
eggs, or if it has young, it may adopt either mode of escape, while
if it has eggs it has no choice but to remain quiet over them.... The
act of rolling up into a passive ball may be performed (_a_) _under
compulsion_, as when it is her last resort in self-defence; (_b_)
_under a milder provocation_, as _one_ of three courses of behaviour,
as when the resting-place is turned up to light, and the choice is
offered between remaining quiet in place, creeping away at leisure,
or rolling into a ball and dropping to the bottom; (_c_) or finally,
_under no special external stimulus_, but rather _from internal_
motive, the normal demand for rest and shady seclusion, presumably very
strong in _Clepsine_ after gorging itself with the blood of its turtle
host.”
Professor Whitman rightly regards the act of rolling into a ball as
instinctive, and due to natural selection. But he does not undertake
to discuss the question as to how much intelligence, if any,
_Clepsine_ may have. Nor, indeed, is it an easy matter to determine.
The differential reaction according as the animal has eggs or not
suggests intelligence; but it may be instinct varying according to
the conditions of stimulation external and internal. The different
behaviour which may be seen in different cases when a stone is turned
to the light again suggests intelligence, but again may be determined
directly by the conditions of stimulation. Prompted by Dr. Whitman’s
observations, I endeavoured to determine whether a leech would grow
accustomed to frequent gentle stimulation with a camel’s-hair brush,
and cease to react under circumstances which were followed by no ill
effects. But though I incline to think that this is the case, the
observations were not such as to be satisfying and convincing. If
intelligence be present we seem to find it in an early and rudimentary
state.
Observation, we must confess, seems to afford little indication of the
conditions under which intelligence first makes its appearance in the
animal kingdom. And if we turn to general considerations, which at the
best afford uncertain guidance, little light is thrown on the subject.
If we accept the view already indicated,[71] that the nerve-centres
which are concerned in the conscious control begotten of experience
are independent of those primarily concerned in normal reflex action,
we may perhaps believe that the simplest nervous system, worthy of
the name, contains both these elements, and that in the course of the
evolution of nervous systems in higher and higher grades, there go on
_pari passu_ the further differentiation of these elements, and the
progressive integration of reflex and control centres into a closely
connected and effective whole. Not that any expression of the facts, if
such they be, in terms of an evolution formula, adds anything to our
knowledge of the organic _modus operandi_. We know but little of the
intimate nerve physiology of even the highest invertebrates. We see
ample evidence of the control of behaviour in the light of individual
experience. Of any detailed knowledge concerning the manner in which
this control is effected we do not seem to possess more than the rude
initial phases.
When we compare, however, the several grades of intelligence which
observation suggests, and when we watch the conscious development of
the more intelligent animals, we seem to find evidence of the growth
of a system of experience, at first in very close touch with inherited
modes of procedure, but gradually acquiring more of independence and
freedom. Increase of the range and complexity of behaviour brings
with it, not only increase in the range and complexity of experience,
but also--what is, perhaps, even more essential to effective
progress--greater unity and closer connection into a well-knit whole.
And with this greater unity and closer connection there goes what one
may term a condensation of experience by an elimination of detail and
the survival of essential features repeatedly emphasized. This is
analogous in the development of intelligence to the generalization
and abstraction which play so important a part in the development of
reason. It affords, in fact, the data which reflection utilizes in the
purposive and intentional condensation and concentration of knowledge
at a higher stage of mental development.
The omission of detail and the survival of the salient features is well
known to us in the familiar facts of memory. We have seen thousands
of sheep and oxen, no two of which are probably alike in all their
external details as presented to vision. But we remember what a sheep
or an ox looks like, and many of us can form a visualized image of
either of these animals. This, however, is not the re-presentative
image of any particular sheep or ox. It is what psychologists term a
generic image. It is like a composite photograph made by superimposing
on the same plate a number of individual images so that the salient
features which all possess in common stand out clearly by their
coincidence on the plate, while the distinctive details are but
dimly presented. Thus does memory preserve the essentials common
to many impressions while the distinguishing details are lost and
fade, eliminated by forgetfulness. And thus in the experience which
intelligence practically utilizes are the net results of a thousand
particular impressions condensed in one effective image.
Condensation of experience is also effected by the elimination, under
the guidance of consciousness, of those modes of behaviour which are
not efficacious--a process to which Professor Mark Baldwin applies
the phrase Functional Selection. There is a tendency at first to the
overproduction of relatively useless actions. The multifarious random
movements of the human infant, though their inexactness renders the
child terribly helpless, afford a wide store of plastic material which
intelligence can guide to its appropriate use. And the prolonged period
of pupilage in the child is correlated with an unsurpassed range of
combination and recombination of the abundant plastic material. The
hereditary legacy, though it contains fewer drafts for definite and
specific purposes than are placed to the credit of an animal rich in
instinctive endowment, affords a far larger general fund on which
intelligence may draw for the varied purposes of the freer financial
existence of a rational being.
The relatively helpless young of many of the higher mammalia exhibit
also much overproduction of seemingly aimless movements. But from
these intelligence selects those which are of value for the purposes
of life--those which experience proves to be effective. These--the
relatively few--afford the motor impressions which by repetition stand
out in experience, while the rest lapse from memory and are eliminated
from experience as they are eliminated from practical performance. This
is a great gain. Motor experience is rendered generic; the composite
image that is retained is the net result of effective behaviour; and
all that is valuable in the acquisitions of early life is condensed
within manageable limits.
This process of rendering generic the particular items of a widening
experience has a marked effect in the development of the conscious
situations in the light of which behaviour is intelligently guided.
It is not the master holding this whip or that ball which suggests
to the dog a hiding or a scamper; it is a generic situation with
interchangeable details. It is not this, that, or the other previously
unseen cat that at once determines the situation for the fox terrier;
the particular animal has never entered into his past experience: it is
the fulfilment of the essential conditions of the generic image that
is operative in behaviour. The experience of animals must inevitably
become in large degree generic by the elimination of the unessential
and survival in re-presentative consciousness of the salient elements
in many slightly diverse situations.
Stated in terms of this conception, the familiar phenomena of mimicry
are due to the fact that the mimicking form accords sufficiently well
with the generic image to carry the same suggested meaning. As is
well known, the model has been proved in many cases to be unpalatable
or hurtful, while the mimic is in itself neither the one nor the
other. The drone-fly, _Eristalis_, mimics the drone. And it has been
urged that this cannot be a true case of mimicry, since the drone
is harmless, though the female and “neuter” bees are possessed of
stings. But I have satisfied myself by experiments with young birds,
that (1) after experience with bees drones are avoided, and (2) that
after similar experience drone-flies are also left untouched. Hence it
seems that all three fall within the same generic image, the points of
resemblance outweighing the differences in detail--as they do, indeed,
with many men and women.
Such examples of mimicry belong to what is known as the “Batesian
type”--so called after H. W. Bates, who, in 1861, discussed its
occurrence among Amazonian insects in the light of the theory of
natural selection. There are, however, certain groups of insects
which, although themselves “protected,” possess common warning
colours, causing them to resemble each other. These are sometimes
classed under the head of “Müllerian mimicry”--so called after Fritz
Müller, who, in 1879, first offered an explanation of the facts
based on the theory of natural selection. He suggested that such
mutual resemblance is advantageous to both protected forms, since it
lessens the number of those which are killed by young birds and other
animals while they are learning by experience what to eat and what
to leave. For, as the result of careful observation, Mr. Frank Finn
concludes “that each bird has to separately acquire its experience,
and well remembers what it has learnt,”--a conclusion with which, as
already stated, my own observations are entirely in accord. There is
therefore a certain amount of destruction of even well-protected forms
by young and inexperienced birds. If, then, two such forms resemble
each other, the acquisition of experience is thereby facilitated and
the amount of destruction reduced, on the assumption that the two
fall within the same generic image. Upholders of natural selection
are not, indeed, at one in accepting this explanation, and further
observation is unquestionably needed. It is not improbable, however,
that common protective coloration, such as the banding of yellow and
black, seen in such different forms as the caterpillar of the cinnabar
moth and the imago of the wasp, is of mutual utility. The following
experiment was made with young chicks. Strips of orange and black paper
were pasted beneath glass slips, and on them meal moistened with
quinine was placed. On other plain slips meal moistened with water
was provided. The young birds soon learnt to avoid the bitter meal,
and then would not touch plain meal if it were offered on the banded
slip. And these birds, save in two instances, refused to touch cinnabar
caterpillars, which were new to their experience. They did not, like
other birds, have to learn by particular trials that these caterpillars
are unpleasant. Their experience had already been gained through the
banded glass slips; or so it seemed. I have also found that young birds
who had learnt to avoid cinnabar caterpillars left wasps untouched.
Such observations must be repeated and extended. But they seem to show
that one aspect of the Müllerian theory is not without some facts in
support of it; and, so far as they go, they afford evidence that black
and orange banding, irrespective of particular form, may constitute a
guiding generic feature in the conscious situation.
It may be said that the generic condensation of experience here
indicated implies the formation of general and abstract ideas, and
that we cannot in face of the evidence accept Locke’s dictum that
abstraction is “an excellency which the faculties of brutes do by no
means attain to.” Romanes contended[72] that “all the higher animals
have general ideas of ‘good-for-eating’ and ‘not-good-for-eating’ quite
apart from any particular objects of which either of these qualities
happens to be characteristic,” and he quoted with approval Leroy’s
statement,[73] that a fox “will see snares when there are none; his
imagination, distorted by fear, will produce deceptive shapes, to
which he will attach an abstract notion of danger.” According to such
views animals form concepts; and concepts belong to the sphere of
rational thought. It is not my intention to enter at length into the
refinements of psychological distinction. Many psychologists, however,
seek to distinguish between, on the one hand, the predominance by
natural emphasis, of certain qualities, such as that of being suitable
for food, and, on the other hand, the intentional isolation of these
qualities for the purposes of thought and rational explanation.
Abstraction they regard as a deliberate process applied with rational
intent to the material afforded by experience and reflection.
Generalization, too, they regard as deliberate, and carried out with
like intent. The result is not merely a composite or generic product,
but something more subtle and less dependent on sense. “All trees
hitherto seen by me,” said Noiré, “leave in my imagination a mixed
image, a kind of ideal presentation of a tree. Quite different is my
concept, which is never an image.” The concept “tree” is a deliberate
synthesis of abstract qualities intentionally isolated, and recombined
in accordance with the general relationships which subsist between them.
If we accept this distinction, if we regard abstraction and
generalization as intentional mental processes carried out with the
rational intent of discovering the relationships of phenomena with the
object of explaining them and recombining their essential features in
an ideal scheme of thought, we shall probably admit, with John Locke,
that these are excellencies which the faculties of brutes do by no
means attain to. But we shall none the less see that the predominance
of certain salient features in experience by reiterated emphasis in
association with natural needs, and the development of generic in place
of merely particular re-presentations will afford the appropriate
material for abstraction on the one hand, and generalization on the
other. Intelligence supplies the embryonic mental structures from
which, under the quickening influence of a rational purpose, abstract
and general ideas may be evolved.
The essential features of the evolution of intelligence seem, then,
to be, first, the development of controlling nerve-centres, by which
the responsive action of reflex automatic or instinctive centres
may be checked, augmented, or modified; secondly, the increased
differentiation and integration of these control centres with extension
of the range and complexity of experience in close touch with practical
needs; thirdly, the condensation and concentration of experience by
the formation of generic products through the reiterated emphasis
begotten of recurrent situations having certain salient features
in common, though differing in details; and fourthly, an increased
plasticity of behaviour, especially in early life, enabling an animal
to deal effectually with an environment far less simple than that
to which the more stereotyped instinctive behaviour is fitted by
inheritance to respond. And this evolution of intelligent behaviour is
working its way up to, though as such it cannot reach, the succeeding
phase of mental evolution in which the data, supplied by intelligence,
are treated with a new purpose for higher ends in the rational thought
which seeks to explain the phenomena, and frame an ideal scheme of
their relations and interconnections.
Two further points may be noticed. First, that it is during the early
and plastic days or months of life that intelligence is setting
its seal on animal behaviour, and stamping it with its distinctive
character. Adult life is very much what youth has made it; and old
age is stereotyped through habit. In times of progress, the character
of the race is determined by plastic possibilities of the young.
Among them it is that the incidence of elimination makes itself felt,
resulting in the survival of those whose intelligence can mould
behaviour in accordance with the new circumstances of a wider life.
Secondly, this selection of the intelligent involves the survival
of those in whose higher brain-centres there is room for a greater
range and variety of interconnection by means of associating fibres.
It involves a selective survival of the larger and more finely
organized brains. It is probable, as Professor Ray Lankester has
recently indicated, that the ridiculously small-brained mammals and
reptiles of the past were creatures of instinct with little capacity
for intelligent control. Their lives were simple, and their enemies
and competitors no better provided with higher brain-centres than
themselves. Stereotyped instinctive behaviour sufficed to enable them
to hold their own, and meet the requirements of a life of dull and
unprogressive monotony. Strength without cunning made these big-framed
animals for a while masters of the situation. But among those existing
animals whose skeletons indicate an analogous zoological position,
there is none which exhibits a cerebral development so poor. And we
may fairly conclude that the fact that these huge creatures have left
no lineal descendants may be taken as evidence of the importance and
value, in evolution, of that cerebral tissue which is the organic basis
of intelligence. The higher brain contains the potentiality of that
experience without which the evolution of intelligent behaviour in any
race of vertebrate animals is impossible.
V.--THE INFLUENCE OF INTELLIGENCE ON INSTINCT
We have seen that the relation of instinct to intelligence is
essentially that of congenital to acquired behaviour. We have seen,
too, that in the Lamarckian interpretation what is acquired in the
course of life may be transmitted through inheritance, and thus the
intelligent behaviour of one generation may become instinctive and
congenital in the next. But serious biological difficulties stand in
the way of the acceptance of this interpretation; there is, moreover,
little or no evidence of the assumed transmission to offspring of any
acquired modifications of structure or behaviour. We have, therefore,
been led to infer that instinctive behaviour has been evolved through
the selection of adaptive variations of germinal origin, the influence
of intelligence being restricted to the fosterage of co-incident
variations, that is to say, of those congenital variations which
coincide in direction with the acquired modifications of behaviour due
to intelligence. It is clear that on this interpretation the influence
of intelligence on instinct is more indirect and less simple than that
implied by the Lamarckian hypothesis. Intelligence and instinct are
in large degree independent, though there is continual interaction
between them. We have now to consider the nature of this interaction,
and to this end we must indicate the relation of acquired modifications
to the hereditary groundwork of the animal constitution.
The basal fact is, that the bodily tissues are subject to a certain
amount of structural change during the course of individual life in
accordance with the amount of functional strain put upon them. The
labourer’s thickened skin, the enlarged and strengthened muscles of
the athlete, the juggler’s acquired suppleness are familiar cases.
Less familiar instances are afforded under abnormal conditions.
Should one kidney from any cause be slowly destroyed, the other will
slowly enlarge to carry on the increased work of elimination of waste
products; when the larger shin bone of a dog has been removed after
injury, the smaller bone becomes thickened to bear the added strain;
new joint surfaces are sometimes formed where bones have been broken
and the natural joints injured.
One may say that the normal development of any structure depends upon
a due amount of use. But, since in the course of strenuous life any
organ is from time to time subject to an abnormal amount of strain, it
must be fitted to respond to a super-normal call on its strength and
functional activity. Were the heart and the lungs, for example, unable
to meet the greatly added drain on their energies, due to unwonted
and severe exertion, collapse, perhaps death, would ensue if such
exertion were imperatively demanded under special circumstances. And
it is clear that many wild animals must be not infrequently placed in
such circumstances as will subject their muscular structures and the
functional activity of their organs of circulation and respiration to a
strain nearly up to their extreme limits of endurance. The carnivorous
hunter would often fail to secure his prey if his organization were
unequal to a hard and prolonged chase; the hunted prey would not
survive to procreate his kind if he fell a victim to the first pursuer
through inability to stand the exertion necessary to enable him to
make good his escape. It is thus, we may believe, through natural
selection that a sufficiently high standard of strength and functional
endurance is maintained. The failures in these respects are steadily
eliminated. It is difficult to realize the great strain put upon a
bird’s organization by the migration flight. Some ten times as many
birds leave our shores in the autumn as return to them in the following
spring. What proportion of these is weeded out in the act of migration
we do not know; but we may be sure that only those fitted to stand a
severe test of physical endurance return to rear broods which shall
inherit in large degree similar vigour of constitution.
Two factors, then, determine the limits of efficiency in the bodily
organs--heredity and use. And these two co-operate in such a way
that we may say, either that due use is the essential condition of
the effective development of the hereditary powers, or that heredity
serves to condition their effective development through use. But though
closely related, so that each may be regarded as conditional on the
other, they are, if we accept the view that acquired characters are not
transmitted as such, so far independent in that use adds nothing to,
disuse subtracts nothing from, the hereditary store. It is, indeed,
difficult to conceive how, on any view, the absence of the conditioning
factor of normal use can be the efficient cause of a positive
diminution of the balance at the bank of heredity. And Lamarckian
thinkers have not succeeded in placing their conception of the matter
in the clear light of a working hypothesis.
The amount of what we may term “modifiability” by use differs a good
deal in the several organs and tissues. The teeth of carnivora and the
antlers of deer may be cited as structures in which the conditioning
effects of use form a relatively unimportant factor. On the other
hand, the nervous system, with which we are here primarily concerned,
is of all animal structures that in which what is acquired may attain
the greatest importance in the successful conduct of life; the nature
and the range of behaviour affording an index of the amount of
modifiability in this respect.
We have already seen that instinctive behaviour is primarily a matter
of the first occasion on which any given action is performed, and that
many instinctive acts are subject to subsequent modification in the
light of the experience gained during the early performances. The range
of such modification varies both in different animals and also with
respect to different modes of behaviour in the same animal. The more
fixed and deeply rooted an instinct the less readily does intelligence
obtain a hold on it, so as to direct the behaviour into new channels
of better accommodation to the circumstances. M. Fabre describes how
a _Sphex_, one of the solitary wasps, instinctively draws its prey, a
grasshopper, into the burrow by its antennæ. When these were cut off
the wasp pulled the grasshopper in by the jaw appendages; but when
these were removed she seemed incapable of further accommodation to the
unusual circumstances. It would seem an easy and obvious application
of intelligence to seize the prey by one of the forelegs. But this
was not done; and the grasshopper was then left. Intelligence did
not seem equal to meeting the altered conditions presented by the
maimed grasshopper. Still, there was some modification of the normal
instinctive behaviour; and, as Dr. Peckham has shown, there may be more
than Fabre noted. Let us assume the existence of an animal whose every
act is instinctive, whose whole behaviour is marked out in strictly
hereditary lines, no new departures being acquired in the course of
individual life. This extreme case would afford an example of what we
may term completely stereotyped behaviour. On the other hand, let us
assume the existence of an animal with no hereditary definiteness of
reaction, whose every act is intelligent, whose whole behaviour is the
result of individual acquisition. This antithetical extreme case would
afford an example of what we may term completely plastic behaviour.
It is questionable, however, whether either of these extreme types
occur in nature. What we find in our study of animal behaviour is
some intermediate condition in which both factors co-operate, with a
predominance either of stereotyped instinctive response on the one
hand, or of plastic intelligent acquisition on the other hand. And in
the latter case, as such behaviour approaches its ideal limits, we have
modifiability under the circumstances of individual life at its maximum.
The evolution of intelligence as such runs parallel with the evolution
of plastic behaviour; and this plasticity is necessitated by the
variety and the complexity of the conditions of life--a variety and a
complexity requiring many subtle modifications of response to enable
the behaviour to reach accommodation to the changeful exigencies of
diverse circumstances. To meet constant and relatively fixed conditions
stereotyped instinctive responses suffice; and the elimination under
natural selection of those individuals which fail to respond in fixed
ways by specially adaptive behaviour tends to render definite the
hereditary channels of nervous intercommunication. An inherited system
of no little complexity may thus be evolved; of which we have seen
examples in our study of instinctive behaviour. But the essential
condition of the successful working of such a system is constancy
in the environment to which the instinctive behaviour is adapted.
Completely stereotyped behaviour, in its theoretical perfection, is
in exact adaptation to the circumstances. Where instincts are only
relatively perfect, further adaptation is secured through congenital
variation and the survival of the individuals in which the behaviour
is better adapted to the comparatively invariable circumstances.
This is one line of evolution. But the evolution of intelligence is
along independent lines of progress. Both, however, result from the
functional activity of the same nervous system, they jointly determine
the behaviour, they interact not only in the course of individual life
but in the process of evolution, and they are both subject to the
incidence of natural selection, which can determine whether the one
line or the other shall preponderate--whether instinct or intelligence
shall dominate behaviour.
If an answer must be given to the question whether instinct or
intelligence has priority in the course of the evolution of behaviour,
it may be urged that, on theoretical grounds, the claims of instinct
are the stronger. Taking animals as we actually find them, however,
they afford numberless examples of behaviour at first instinctive but
subsequently modified, in greater or less degree, in accordance with
the teachings of experience. Let us, first, assume that the environment
is slowly changing, or has changed, in some definite manner. Such
change would, of course, be relative, and might be due, either to new
conditions brought to bear on the animal, or to the animal being itself
brought, in the expansion of its life, within their influence. The
old instinct is no longer quite adapted to the changed circumstances.
If the change were sufficient in amount, and occurred somewhat
suddenly, variations of instinct might not occur soon enough to enable
the animal to reach adaptation by the gradual process of natural
selection. If dependent on instinct alone the animal would, under
these circumstances, be eliminated. But if intelligence were able to
modify the behaviour to meet the new conditions this elimination would
be prevented. In successive generations intelligence would constantly
modify behaviour in the same manner and in a definite direction.
Meanwhile congenital variations in different directions would occur.
Those which were in directions antagonistic to that dictated by
intelligence would tend to thwart accommodation and render it less
effectual; but those which were coincident in direction would conspire
with accommodation and render it more effectual. The individuals in
which variations of instinct tended to thwart intelligence would be
eliminated; while those in which coincident variations assisted and
aided intelligent modification would survive. Thus intelligence would
lead the way along lines which congenital variations would follow. And
in the course of a number of generations the new instinct would reach
the fully adaptive level, and further modification by intelligence
would become unnecessary unless the environment continued to change yet
more. Individual accommodation of behaviour would in this way determine
the direction of instinctive variation; and yet throughout the process
there would be, strictly speaking, no transmission of the intelligently
acquired characters of the behaviour.
But though under constant and uniform changes in the environment the
net result would be only a guided variation of the original instinct,
under more variable and indefinitely changing circumstances the
result would be different. The higher animals exhibit an intelligent
plasticity which enables them to meet the requirements of the
more complex environment into which their wider life has risen;
for evolution lifts the animal from narrower into progressively
wider spheres of activity and behaviour, so that its environment
becomes relatively more complex. Here stereotyped behaviour would be
rather a hindrance than an advantage. The winning animal in life’s
struggle would be the one in which behaviour was most rapidly and
most surely modified to meet particular needs--the one in which the
teachings of experience were most promptly utilized in effective
action. The inevitable tendency of the evolution of intelligence
must be disintegration of the stereotyped modes of behaviour and the
dissolution of instinct. Natural selection, which under a uniform and
constant environment leads to the survival of relatively fixed and
definite modes of response, under an environment presenting a wide
range of possibilities leads to the survival of plastic accommodation
through intelligence. It is not that intelligence has any direct
influence tending to undermine the hereditary foundations of instinct,
for acquired plasticity is not inherited as such; it is rather that
when the stereotyped and the plastic are pitted against each other in
the struggle for existence in the wider, freer, and more varied life of
the higher animals the plastic survives and the stereotyped succumbs.
Imperfect as is our present knowledge of the manner in which the
nervous connections implied in psychological associations are
established, there can be no question that they are acquired in the
course of individual life; they are modifications of nervous structure
due to a special mode of use under the conditions of experience.
Here, then, in the case of the nervous system, as in that of the
bodily organs before mentioned, two co-operating factors determine
the limits of efficiency--heredity and use. Just as the heart and
lungs must inherit the power of standing abnormal strain if the animal
is to avoid elimination in times of unwonted exertion, so must the
nervous system inherit some reserve power of dealing effectively with
unwonted circumstances by intelligent accommodation, if the animal
is not to fall a victim to such circumstances. In other words, at
times of heightened competition those animals which can draw on a
reserve fund of intelligent accommodation will survive, while the
stupid blunderers will be eliminated. We may term this reserve fund of
intelligent accommodation, this inherited ability to meet specially
difficult circumstances as they arise, _innate capacity_. From the
nature of the case it must be indefinite, for it must carry with it the
ability to meet unforeseen combinations of the environing forces by new
combinations of the results of experience. Its distinguishing mark is
plasticity, in contradistinction to the stereotyped fixity of typical
instinct. And accompanying its evolution there is probably, as we have
seen, a dissolution of its antithesis, instinct. Thus may we account
for the fact that man, with his great store of innate capacity, has so
small a number of stereotyped instincts.
But the dissolution of instincts is not complete. Residua are left
in the inherited mental constitution. And these we term _congenital
tendencies_ and _propensities_. They differ from the typical instincts
in the fact that the definiteness of response has been lost. They
dictate a general trend of action, but the particular application in
behaviour is due to intelligent accommodation. They are commonly spoken
of as instinctive; and their mode of origin justifies the use of the
adjective in association with the term “propensities.” But it must
be remembered that the behaviour to which they lead is not, as such,
wholly instinctive; it is a joint product of instinct and intelligence,
the general trend being due to the instinctive propensity, while the
mode of application is guided by intelligence.
There is, however, another way in which analogous propensities may
be ingrained in the mental constitution, not as residual vestiges of
old instincts, but as congenital rudiments fostered by new habits.
It is a well-known and familiar fact that the frequent repetition of
intelligent accommodation in certain definite lines begets habits,
which so far simulate instincts as to be commonly described in
popular speech as instinctive. Professor Wundt indeed places them
in the category of “acquired instincts”--a usage which we regard as
unsatisfactory, seeing that it tends to mask the distinction between
the congenital and acquired factors in behaviour, and seeing that
we have the well-defined term “habits” for acts rendered to a large
extent automatic through repetition. Lamarckian thinkers regard habit
as the mother of instinct, assuming that the acquired automatism
of one generation may be transmitted to become congenital in the
succeeding generation. This conclusion we provisionally reject,
regarding the basal assumption as at present unproven. But though
we cannot accept the view that habit is the mother of instinct, we
regard it as not improbable that habit may be the nurse of congenital
propensities. Remembering that similar habits are acquired by animals
of the same species throughout a series of succeeding generations, and
assuming that congenital variations are constantly occurring in many
directions, it seems probable that some of these variations will be
coincident in direction with the acquired habits. Thus would arise a
congenital propensity to perform the habitual acts; and should they
be of sufficient importance in the conduct of life to be subject
to the action of natural selection, those animals in which such
propensities were congenital would survive, whereas those in which
no such propensities existed would be eliminated. It is unnecessary,
however, to elaborate this conception further, since it is in line with
that already discussed in considering the influence of intelligence in
fostering a diversion of instinct under changing circumstances. Then we
were considering how habit may lead to a congenital change in an old
instinct; here we are dealing with the development of a new propensity.
Sufficient has now been said to illustrate some of the ways in which
instinct and intelligence interact in the evolution of behaviour. Such
interaction is further exemplified in the social life of animals, which
will be dealt with in the next chapter.