No one doubts today that all Vertebrates, from the Fish to Man,
possess more or less intelligence--namely, the power of forming memory
associations and of learning by experience. But when we come to the
study of Invertebrates (e. g., Insects, Spiders, Mollusks, Worms),
we meet with much divergence of opinion among the authorities. Many
competent investigators have been led to the conviction that the
capacity to learn by experience, to form memory associations, leading
to intelligent adjustment of behavior to environment, resides only
in those animals which possess a true cerebrum and central nervous
system, such as is found only in the Vertebrates. Below these forms,
they conclude, lie only “instinctive reactions” to stimuli--“purposeful
action without consciousness of purpose” (Hartmann). With increasing
complexity of the nervous system, arises the neural mechanism for
memory association, the basis of intelligence; and to “inherited habit”
(instinct) is added deliberate (intelligent) purposeful adaptation
of conduct to a consciously desired end, the underlying motive being
avoidance of pain and the attainment of pleasure, or satisfaction.
A simple illustration of the modification of mere instinct by
associative memory, plus pleasurable or painful effects, is afforded by
Lloyd Morgan’s experiments with chicks.
As is well known, no sooner is a young chick hatched than it begins--by
instinct--to peck at all sorts of objects of about a certain size,
whether they are edible or not. If, however, one of these objects
happens to be a caterpillar of nauseous taste, upon meeting a similar
caterpillar a second time the chick appears to remember its first
painful experience, and refrains from pecking at it, and may even
scrape its bill on the ground as if to wipe off the bad-tasting
substance, so vividly is it recalled. This is an example of associative
memory and “learning by experience,” avoiding the repetition of acts
previously attended by pain or displeasure. “What distinguishes
intelligence from instinct is,” says Professor Holmes, “that in
the latter the connections between acts are based upon hereditary
organization, whereas in the former they are established through
experience.... We have in this modification of instincts through
the pleasurable or painful effects they produce the beginning of
intelligence.”
Such notable psychologists as Mach, Loeb, Holmes, Thorndyke, Morgan,
Whitman, Baldwin, and many others accept as a criterion of intelligence
in animals this capacity for memory association, constituting what the
metaphysicians call _consciousness_.
For most modern psychologists, _an interruption of consciousness is
merely an interruption of the activity of associative memory_. They
speak of the extent of associative memory in the animal kingdom instead
of the extent of consciousness among animals.[1]
If an animal possesses the mechanism for associative memory, then it
possesses, unquestionably, the mechanism for intelligence. Just what
this necessary mechanism is, and in what group of animals it appears in
its simplest form, is at present a debatable question--not to say an
unsolved problem.
On the positive side, we may assume that if an animal can “learn
by experience”--associate the memory of a previous experience with
a present situation, and profit by this association--it possesses
intelligence.
On the other hand, failure on the part of an experimenter to train an
animal to react in a desired way does not afford proof of the absence
of intelligence--of associative memory. It may only prove that wrong
methods have been employed by the experimenter.
Some authorities have found evidences of intelligent reaction to
stimuli, not only in such Invertebrates as the Crab, Crayfish and
Horseshoe Crab, but also in the Octopus, Starfish and even among the
lowly group familiarly known as “Worms.”
Binet went farther and wrote a learned work on “The Psychic Life of
Micro-organisms,” in which considerable intelligence was attributed to
Infusorians. But that was thirty years or more ago.
While no competent writer would assert today that psychic life is
entirely absent in the Protozoa (one-celled animals), it is now
generally conceded that no adequate proof of intelligent response to
stimuli among unicellular animals has so far been forthcoming.[2]
In the opinion of the late Dr. Jacques Loeb, the claim of a number of
investigators that associative memory and therefore of intelligence
as here defined, is possessed by even such multicellular forms as
Worms, Starfish, Sea Urchins, Actinians, Medusae and Hydroids, is
unwarranted by the experimental data. “Claims for the existence of such
memory in these groups of animals,” remarks Loeb, “have frequently
been made, but such claims are either plain romance or due to a
confusion of reversible physiological processes with the irreversible
phenomena of associative memory. The less a scientist is accustomed to
rigid quantitative experiments, the more ready he is to confound the
reversible after effects of a stimulus--e. g., the effects due to an
increase in hydrogen ion concentration--with indications of associative
memory. Learning is only possible where there exists a specific organ
of associative memory, the physical mechanism of which is still
unknown.”
Loeb admitted that associative memory “exists in most mammals,” also
in birds. In the lower Vertebrates this capacity, he thought, was only
_occasionally_ found: “Tree-frogs, for example, can be trained, upon
hearing a sound, to go to a certain place for food. In other Frogs,
_Rana esculenta_, for instance, no reaction is as yet known which
proves the existence of associative memory. Some Fishes evidently
possess memory; in Sharks, however, its existence is doubtful. With
regard to Invertebrates, the question is difficult to determine. The
statements of enthusiasts who discover consciousness and resemblance to
man on every side should not be too readily accepted.”
We must now add, that equal caution should be used in regard to
those authors who contend that intelligence does not exist among
Invertebrates, but only “instinctive reactions to stimuli.” To describe
an act as “instinctive,” moreover, does not explain much. G. Bohn asks:
“What is instinct?” and answers: “A word.”
Mr. Garrett P. Serviss recently received a letter from a citizen of
Philadelphia from which I quote the following paragraph:
“You speak of the intelligence of the Spider. Understanding and
reasoning go hand in hand with intelligence; there is no intelligence
without reasoning or understanding, hence it can be applied to Man.
How do you apply it to the Spider? So, as regarding the Bee and the
Ant, would you not think that their intelligence is simply ‘instinct,’
peculiar to their species for self-preservation?”
Mr. Serviss replied (in part) as follows:
“I see no reason for denying intelligence to animals ranking below Man
in the scale. Both the lower animals and the human species possess what
are called instincts, which are said to act spontaneously, without the
aid of reasoning. No animal, indeed, possesses a greater number of
instincts than Man.
“But if the distinction between instinct and intelligence is to be
based on the employment of conscious reasoning or intelligence, this
faculty cannot be denied to the lower animals, because I believe that
many of them do exercise a power of reasoning, i. e., of drawing
conclusions from observation.
“Natural history books are full of instances of exhibitions of
intelligence by Dogs, Cats, Elephants, Horses and many other
creatures. It is true that some naturalists insist that all of the
apparently intentional and reasoned acts of such creatures are merely
manifestations of instinct, or unconscious responses to external
stimuli, but all naturalists are not of that opinion.”
No, they are not.
Prof. S. J. Holmes says: “Psychologists nowadays with comparatively few
exceptions agree in regarding intelligence not as a faculty standing in
sharp contrast to instinct, as was formerly taught, but as one resting
on a foundation of instinct, and gradually growing out of behavior of
the purely instinctive type. The term intelligence is used here in the
wider sense as embracing all those forms of profiting by experience
through the formation of associations. It therefore includes psychic
activity ranging from simple associative memory to complex trains of
reasoning.”
Paley, in his “Natural Theology,” defines instinct as “a propensity
prior to experience and independent of instruction”; while Spencer
(“Principles of Psychology”) states that instinct is a “compound reflex
action,” which is terse, if not explanatory.
Hartmann’s “purposeful action without consciousness of the purpose” is
a contradiction in terms. “Purpose” implies consciousness of end in
view. One cannot readily believe that when an Orang-utan builds its
platform or “nest” in the boughs of a tree in the jungle it does not
purpose (_intend_) to rest and sleep on it; or that when a Beaver cuts
down a tree in such wise that it invariably falls in the direction of
its _need_ it does not _know_ that it is constructing a hut to live in
that will meet the requirements of the situation in a running stream.
Dr. Wm. T. Hornaday, in his authoritative recent work, “The Minds and
Manners of Wild Animals,” (1922) says:
“Instinct is the knowledge or impulse which animals or men derive
from their ancestors by inheritance, and which they obey, _either
consciously or subconsciously_[3] in working out their own
preservation, increase and betterment. Instinct often functions as a
sixth sense.”
Again: “While avoiding the folly of idealism, we also must shun the
ways of the narrow mind, and the eyes that refuse to see the truth.
Wild animals are not superhuman demigods of wisdom; but neither are
they idiots, unable to reason from cause to effect along the simple
lines that vitally affect their existence.... Some animals have more
intelligence than some men; and some have far better morals.”
Nevertheless, it is still “correct” to say: “Man alone possesses
reason.” Fundamentalists, and even many scientists, find this
phrase acceptable. The “Age of Reason” began with the appearance
of Man on earth, according to orthodox views. “Instinctive
behavior” explains--for many scientists--all acts even of such
highly organized creatures as Ants, Bees and Wasps. Below this come
“tropisms”--obligatory movements made by the organism as a whole in
response to the varied stimuli of its environment.
Then we have the category of “purely reflex” actions of the
organism--the definite but unconscious reaction of the organism to
stimulation of certain nerve-cells.
In the higher microscopic organisms it is admitted that any one of
several reactions to a given stimulus might _occur_, the organism
“trying” (unconsciously) one reaction after another, on the hit or
miss, or “trial and error” method. Man, of course, learns by some
faculty other than “trial and error”--maybe.
Finally, and lowest in the scale of animal evolution, we come to the
Amœba, a unicellular organism apparently lacking even in a rudimentary
nervous system. But this microscopic speck of carnivorous protoplasm
seeks and _pursues_ its zigzagging prey!
While there is no proof that psychic life begins only with
pluricellular animals, thus denying any sort of consciousness of
purpose to even the highest groups (Ciliata) among unicellular
organisms (Protozoa), it must be admitted that no conclusive evidence
of the presence of mind in these lowly organisms has yet been
presented. I shall therefore turn at once to the Metazoa (many-celled
animals) for examples of the intelligence of Invertebrates; beginning
with the lowest in which manifestations of mind are said to appear,
namely, the Earthworm.