Chapter 4
Instinct and Mood
The classic reflex theory postulated that a particular
stimulus always elicited a particular reaction. Where instinctive behavior
in animals is concerned, however, the position is not so simple. Quite
different factors are at work here, and this brings us to a field of inquiry
which is of especially great importance to the assessment of human behavior.
As we have already noted, the motor cells which control
hereditary coordinations are constantly active. They produce an almost
steady flow of coordinated impulses, which are normally prevented from
reaching the muscles by the IRM's. Only when the appropriate key stimulus
has effected its release can the movement run its course. If a hereditary
coordination is not released for a considerable period-if the animal encounters
no key stimulus-this can engender mounting excitation. The animal grows
restless and starts actively to seek the liberating stimulus situation.
This is what the phenomenon we refer to as instinct really is. In such
a state of excitation, far weaker key stimuli than usual suffice to elicit
the appropriate instinctive action. If the animal fails to find even these,
the hereditary coordination can sometimes operate without any stimulus
or incentive whatsoever-spontaneously, in fact. The inhibitory block is
thrust aside, and the "lock" springs open without the requisite key.
Lorenz observed this in a starling which he had reared
indoors. The bird received sufficient food but had no chance to
(original book page 42)
work off its flying and insect-hunting coordinations.
It accordingly indulged in the following behavior at regular intervals:
It flew from its perch and snapped – although the room was completely insect-free
– at thin air; then, returning to its perch, it performed the movements
typical of insect killing and, finally, swallowed. Analogous behavior occurred
in geese which Lorenz fed with grain on dry land. Although replete, they
still showed an impulse to enter the water and upend at random. In both
cases the birds' stomachs were full, so they could not have been hungry.
Despite this, they obeyed an urge to perform particular movements spontaneously,
without the need to eat, and obviously for the sole purpose of activating
the appropriate hereditary coordinations.
A creature's increasing readiness to perform a particular
instinctive action is described by the ethologist as a specific inclination
or appetency. These burgeoning appetencies can be recognized externally
by certain characteristic movements which are known as movements of intent.
The creature, made restive by one of its instincts, suggests by the nature
of its movements which of its innate motor patterns is agitating for release.
A greylag goose, for example, when in "takeoff mood," performs aiming motions
with its head for a period before taking the air. In the case of food-minded
sharks in the Indian Ocean, Eibl and I observed that they moved their heads
from side to side as though actually dismembering their prey.
Surrogates, or substitutes, are also employed as a means
of working off appetencies. This can be seen in creatures which live in
communities and among which the mutual grooming of fur and skin forms part
of the innate behavior repertory. Keep such creatures in isolation and
they will lack the opportunity to carry out these actions. Hence, they
will often invite their keeper to let himself be groomed by them. Again,
female rats are in such a strong retrieving mood ("retrieving" is the term
applied to the instinctive act of salvaging young which crawl out of the
nest) for some days after giving birth that they frequently use their own
tail or one of their hind legs as a surrogate. They pick up their tail,
carry it into the nest, and deposit it there; or they grip one of their
hind legs and hobble back with it on three legs as if it were a baby rat.
(original book page 43)
Zoos afford a demonstration that the same impulses often
occur in varying strength among different species of animals. Lions, for
example, exhibit a weaker urge to move than wolves, a fact which stems
from their dissimilar ways of life. Wolves bring down their prey by tracking
and pursuit, whereas lions usually lurk in hiding until a suitable quarry
approaches. Thus the lion does not mind if it obtains food without exertion
in captivity. Its instinctive control is adjusted to a correspondingly
quiescent mode of existence. With the wolf, food satisfies hunger but not
the locomotive appetency normally associated with the acquisition of food.
It thus paces restlessly up and down its cage in order to work off its
pent-up excitation.
Spitz and Ploog observed a similar state of affairs in
children. If babies sucked a given quantity of milk from a bottle in twenty
minutes, they fell asleep peacefully. If the teat aperture was enlarged
so that they could imbibe the same quantity in half the time, they showed
their dissatisfaction by continuing to suck and by crying. Their hunger
was assuaged, but their appetency for sucking had not been fully realized.
If they were given the empty bottle, they continued to suck for another
ten or so minutes and only then were satisfied. Bucket-fed calves offer
a" similar example. They develop the habit of sucking other calves or the
rings on their stall chains.
Creatures in an appetitive condition become less receptive
to key stimuli which elicit other behavior patterns. A hunting minded animal
must be presented with far stronger sexual stimuli before it makes the
transition to mating behavior, and vice versa. As soon as the most pressing
impulse has been satisfied, however, the animal regains its normal receptivity
to other stimuli.
Lorenz speaks of a "parliament of instincts" – an extremely
graphic metaphor. Just as members of a legislative body compete to submit
their proposals and put them into effect, so instincts jostle for a chance
to take the floor and issue their coordinated commands. They wait to take
charge of the body and control it. If no such opportunity presents itself,
heightened excitation results: The instinctive act in question becomes
easier to elicit and can even take place at random and without special
incentive.
(original book page 44)
Lorenz compares this process of mounting excitation with
a liquid gradually rising inside a vessel until it finally overflows. Tinbergen
and von Holst also refer to the internal damming of energy specific to
action until it eventually spills over. Another graphic idea used to illustrate
this process was borrowed from physiology, which speaks of a lowering or
raising of stimulus thresholds. The higher a threshold, the harder it is
to cross, and the same metaphor has been applied to stimuli which elicit
instinctive actions or reflexes. A rise in the stimulus threshold signifies
that correspondingly stronger stimuli are required to elicit the appropriate
reaction. A fall entails that a relatively small stimulus can cross the
threshold and eliminate the block.
Many ethologists have investigated the factors responsible
for lowering the inhibitory stimulus threshold in particular forms of instinctive
behavior – in other words, for prompting the emergence of particular instincts.
Exhaustive inquiries showed that disregarding the spontaneous arousal of
excitation, a creature's specific inclination is also affected by external
and internal factors.
Thus – to quote an external influence – it is lengthening
hours of daylight that put the male stickleback into a procreative mood.
The responsible "member" in its parliament of instincts starts to wield
influence and causes it to be assailed by a definite restlessness. As yet,
the fish neither dons its mating garb nor exhibits any courtship or aggressive
behavior. Sticklebacks migrate in shoals from their deep winter quarters
to warmer, shallower waters. Once there, every male seeks a weed-stocked
spot and establishes its territory. Only then does it put on mating dress
and become receptive to other stimuli. If sticklebacks are captured during
migration and placed in a basin which contains no plant life of any kind,
they remain in a shoal and do not change color, simply because none of
the males can mark out a territory of its own. Plant some weed in one corner,
on the other hand, and one of the males will soon detach itself from the
rest, take up station there, establish its territory, change color, and
become procreatively inclined. In this case, therefore, the growth of procreative
inclination is brought about by two factors of an external nature: first,
lengthening hours of daylight; and second, the discovery of plants which
lend them-
(original book page 45)
selves to the establishment of a territory (and nest building).
As a result of these external stimulus situations, the "member of parliament"
in the stickleback's central nervous system responsible for sexual behavior
gains influence and assumes control of the body to an increasing extent,
while other members are obliged to take a secondary role for the time being.
One example of an internal influence is the operation
of hormones. It has been ascertained that when the female collared turtledove
sights a displaying male, its ovaries release progesterone into the blood.
The effect of this hormone is to arouse a disposition to brood somewhere
between five and seven days later. Lehrmann, who experimented with eighty
pairs of these doves, injected them with progesterone seven days before
bringing the males and females together. When he offered them eggs at the
same time as he brought them together, the pairs immediately embarked on
brood-tending activities, which they would not normally have done. This
was yet another instance of the ease with which instinctive behavior can
be distorted and diverted from its natural course-in other words, of its
rigidly mechanical nature. In this case, inclination was induced by a hormone.
Introduce this into the bloodstream prematurely, and the instinctive member
gains ascendancy correspondingly early.
Other instincts represent a further internal influence
on the individual instinct. As we have already noted, the growth of an
appetency renders a creature less receptive to other key stimuli. More
precisely, a fall in one stimulus threshold raises the stimulus thresholds
of other instincts. As the ethologist puts it, one instinct suppresses
another, and there are numerous examples of such suppression. In birds,
for instance, the inclination to brood substantially raises the stimulus
threshold of flight behavior. Flight is harder than usual to induce when
a bird is brooding – a fact for which the above line of reasoning provides
a concrete and mechanical explanation. Similarly, repugnance can suppress
a hen's willingness to peck for food. Obvious as this may seem, it is attributable
to certain very specific reroutings in the bird's central nervous system.
If a hen gets something objectionable in its beak, this can – depending
on the strength of the stimulus-result in as many as four in-
(original book page 46)
nately fixed reactions. It stops eating, extends its neck,
makes movements with its tongue, and excretes saliva. If the aversion is
very strong, it shakes its beak. Finally, it wipes its beak on the ground.
Even if the bird performs only part of this motor sequence, its appetency
for eating will – as quantitative experiments have shown – be diminished.
Inclination toward one form of instinctive behavior can,
however, enhance the inclination toward another. When this happens, the
ethologist says that the two instincts are positively correlated. Many
creatures with an urge to eat can simultaneously experience an increased
urge to fight. One very interesting point to note is that this correlation
need not be common to males and females of the same species – indeed, that
it can be diametrically opposed. In the male cichlid, for example, the
flight mood suppresses preparedness for sexual behavior-that is to say,
the fish loses interest in females when frightened. Aggressive inclination,
on the other hand, is positively correlated with sexual behavior. In other
words, if the fish is aggressively inclined, its preparedness for sexual
behavior is intensified. In the female, the situation is reversed. If the
female is fear inclined, this can actually lead to an intensification of
its preparedness for sexual behavior. Conversely, mounting aggressivity
causes a diminution of sexual preparedness – that is to say, an aggressively
inclined female is uninterested in sex. A similar difference between male
and female behavior has been observed in other creatures as well.
Many hereditary coordinations, too, have an affinity
to the extent that several of them combine to build up one form of instinctive
behavior. A cat's preying behavior, for instance, involves the hereditary
coordinations of lurking, stalking, pouncing, leaping, and fishing. These
are performed in a definite order and thus influence one another. On the
other hand, each such hereditary coordination has its own appetency. A
cat which has lacked the opportunity to perform one or another of these
actions for some time will search for a suitable stimulus situation, if
only to be able to fish or pounce for the sake of so doing. The mouse thus
becomes the object first of one and then of another procedure, and even
a ball of wool can serve as a substitute.
On the basis of these and other observations, Tinbergen
(original book page 47)
formed the conclusion that individual instincts are constructed
along hierarchical lines. The parliament of instincts comprises not only
members but various ministries, each of which consists of a certain number
of officials. These officials vary greatly in their relationship to one
another, and each of them seeks to exercise independent authority – in
other words, strives to control the body in a particular way.
What emerges from this is a picture of the animal organism
which diverges from the traditional view. That which we habitually regard
as a single unit breaks down into a number of authorities, each of which
comports itself in a relatively autonomous manner. In terms of this picture,
the body alone is a unit. It is not controlled by one key authority, however,
but by hierarchically constructed ministries, one or another of whose ministers
is always seizing power for brief periods.
Von Holst and von Saint-Paul acquired even deeper insights
into this problem by cerebral stimulation in chickens. Having introduced
electrodes into the brain by surgery, they were able to probe individual
centers and stimulate them artificially by means of weak electric shocks.
This enabled them to tell which form of behavior was controlling the current
nerve structure. The tiny electrodes caused the birds no pain or discomfort.
When they recovered from the anesthetic, they were completely unaware both
of the electrodes and of the gossamer-fine wires emerging from their heads.
The results of these experiments in stimulation were
very informative and are recorded in instructional films. One of these
shows a cockerel seated contentedly on a laboratory table. Stimulation
of a particular part of the brain ensues. At once, the cockerel stands
up and starts to peck at the tabletop. There is nothing there to pick up,
but as soon as the relevant spot is stimulated, the cockerel pecks like
an automaton. Stimulation of another spot results in the cockerel's remaining
seated but looking around. When the voltage is increased (approximately
from .1 volt to .3 volt), the bird stands up and starts to cluck. A further
increase in voltage and it walks about and evacuates. Yet another increase
and it turns around, squats down, and points its beak in a certain direction.
Finally, at about .9 volt, it takes off, emitting a series of cries. In
this case, gradually
(original book page 48)
increased stimulation elicited various hereditary coordinations
in regular succession. In fact, the cockerel exhibited all the behavior
patterns with which it would normally have greeted a potential invader
of its territory. When von Holst stimulated the calm, seated cockerel with
.9 volt right off, the intermediate phases disappeared and the bird flew
off screeching. If he stimulated the same points several times, the result
was exhaustion and a raising of the stimulus threshold such as can be observed
under natural conditions.
Von Holst and von Saint-Paul were able to induce almost
any hereditary coordination in poultry by artificial means. It turned out
that many hereditary coordinations can be activated from a variety of points
in the brain. One example was clucking and another walking. These hereditary
coordinations occupy a very subordinate position within the hierarchy of
instinctive movements and come into operation in the course of various
behavior patterns. For instance, clucking is a concomitant of brood-tending
behavior, as well as of the activated urge to flee. Again, the hen walks,
or takes steps, not only when in quest of food but also during aggressive
action and copulation. Lorenz christened these very simple hereditary coordinations
"tool activities" because they are useful for various purposes. It is evident
that the circuits in the brain are so disposed that various instincts make
use of these basic movements, each within the context of its particular
motor flow.
Simultaneous stimulation of different points enabled
von Holst and von Saint-Paul to explore more fully the phenomenon of correlation,
which we have already discussed. By means of such double stimulation they
established that seven different permutations occur in response to the
activation of different instincts. Two movements can, first, be superimposed
– for example, simultaneous stimulation of the points responsible for pecking
and head turning can result in the bird's pecking and turning its head
at the same time. Second, two movements can compromise –
for example, stimulation of "observing" and "looking
around" (for danger) can cause the chicken to perform both movements but
with halved intensity. Third, stimulation of "looking around" and "eating"
leads to vacillation, or a condition in which the bird alternately eats
and keeps watch.
(original book page 49)
Fourth, simultaneous stimulation of "turn right" and "turn
left" can produce neutralization – the bird's head turns neither right
nor left but remains centered. Fifth, simultaneous stimulation of two impulses
can induce a transformation whereby the two stimulated impulses release
a third, so that the bird performs an entirely different movement: "Pecking"
and "escape," stimulated simultaneously, can produce deterrent screeching.
Sixth, one impulse can suppress another, so that simultaneous stimulation
elicits one form of behavior in full and only a vague suggestion of the
other (in conjunction with the first). Seventh, one impulse can wholly
inhibit another so that only the dominant partner appears in response to
double stimulation.
Similar experiments in cerebral stimulation have since
been carried out by other authorities. One noteworthy discovery concerns
rats which were trained to carry out their own cerebral stimulation by
depressing a key. A spot in the brain had been found which the animals
clearly enjoyed stimulating. One rat, which stimulated itself more than
50,000 times in a twenty-four-hour period, became positively addicted to
this particular stimulus and released it almost incessantly.
One phenomenon which has not been altogether explained
is that completely aimless behavior patterns occur in animals under conditions
of conflict. For example, fighting cockerels whose flight tendencies have
been activated by their adversaries start to peck at the ground. Nothing
could be less likely than that they should wish to seek food at this juncture,
yet they go through the appropriate motions. Tinbergen ascribed this to
an energy surplus which finds no outlet and consequently jumps to another
nerve track. His name for this often observed process was displacement.
It is also possible, however, that this phenomenon is attributable to the
transformation noted by von Holst, whereby the simultaneous activation
of two impulses releases a third. We shall revert to such movements in
greater detail when discussing human gestures.
Lorenz adduced numerous examples to show how instincts
like the organs of a living creature-adapted themselves to changing environmental
conditions in the course of evolutionary history, and how they were also
molded by natural selection. Interestingly enough, instincts often showed
themselves to
(original book page 50)
be more rigid and "conservative" than the organs with
which they operated. The ancestors of the modern stag, for instance, had
no antlers but a considerably more effective set of teeth with which to
defend themselves. In their case the purposive movement of teeth grinding
developed into a warning signal. Fossil discoveries show that the strongly
developed canines underwent gradual involution as time went by, and today
stags defend themselves with their hoofs and antlers. The instinctive movement
of teeth grinding was retained as a threatening signal, however, and thus
showed itself more conservative than the organs on which it depended.
Lorenz verified substantial modifications of instinct
in domestic animals. By protecting them from their natural foes and the
rigors of the climate, man influenced natural selection by a process known
as domestication. In the realm , of movement, Lorenz found that long chains
of hereditary coordinations disintegrated as domestication progressed:
In other words, dedifferentiation took place. Many innate releasing mechanisms
(IRM's) likewise lost their selectivity, that is to say, no longer responded
to key stimuli with the same precision in domestic animals as in the wild
species from which they were descended. In their case, the "lock" of instinctive
action can be opened by many more "keys." Instincts themselves changed,
too. Many of them, e.g., the social instincts which help to keep animal
communities together, regressed. Others, those of eating and mating, gained
strength or became hypertrophied.
Similar forms of instinctive decay have also occurred
in the course of natural evolution. Not only were they of great importance,
but they formed a prerequisite of the learning process which we are about
to discuss, for the higher vertebrates could acquire increased adaptability
only by developing a less rigid innate structure. Only because their rigid
hereditary fixations partly disintegrated were these creatures able to
improve their behavior by learning. To quote Whitman, one of the earliest
pioneers of behavioral research, failures of instinct were the open door
by which individual experience could "enter" the animal and modify its
behavior.