"An animal, having learned the short form of maze in terms ofkin- sesthesis, should, when the maze is suddenly lengthened, attempt to turn into the blank wall at Q'; and run into the cmIs de sac, B. G, and 11. Similarly, when the animal has learned the long form, it will, when the maze is shortened, butt squarely into the end of the alley, e.g., at 1.
THE DELAYED REACTION (A in this instance). If he goes wrong he is punished. The delay (from moment of turning out light to moment of releasing animal) Fig. 27. Apparatus Used in Studying the Delayed Reaction (After Hunter, Behavior Monographs, Ser. No. 6, p. 25) is gradually lengthened until a limit is reached beyond which the animal cannot successfully react.
BIBLIOGEAPHY Hess, C, Vergleichende Physiologie des Gesichtssinnes. Jena, 1912. Mast, S. 0., Light and the Behavior of Organisms. New York, J.
Wiley & Sons, 1911. Pfungst, O., Clever Hans. New York, Henry Holt, 1911. Yerkes, R. M., and Morgulis, Sergius, " The Method of Pawlow in Animal Psychology," Psych. Bull., 1909, VI, 257. Yerkes, R. M., and Watson, J. B., "Methods of Studying Vision in Animals," Behavior Monographs, Ser. No. 2.
CHAPTER IV OBSERVATIONAL AND EXPERIMENTAL STUDIES UPON INSTINCT Use of term. — Broader definition of term reflex demanded. — Content of term reflex as used in behavior. — General types of instinct. — Methods of studying instinct. — Various results obtained by the method of field observation. — Instinctive activity of birds: the noddy tern. — Instinctive activity of reptiles. — Instinctive activity of fish. — Special forms of instinctive activity in fish. — Results of the experimental study of instincts. I. The initial performance of some instinctive acts. II. Serial unfolding of instinctive acts of young captive animals: (a) Guinea pig; (&) Rat; (c) Mon- key; (d) Sooty tern. III. Quantitative study of improvement of instinctive function. IV. Modification of instinct through social influences. V. Hereditary character of certain instinctive acts and traits. VI. Waning of instinct: loss through disuse, etc.
Use of term. — Modern writers have given no fixed mean- ing to the term instinct. The word is in common usage in a number of different departments of study, — philosophy, psychology, and biology. These separate divisions use the word in widely different ways. Probably no other term, unless it be that of consciousness, is more handicapped by its history. As one wades through the enormous literature and meets the widely different meanings attached to it, one is almost tempted to employ some other word. But in spite of its past the term is short, useful, and convenient. The student of behavior has come to look upon instinct as a combination of congenital responses unfolding serially under appropriate stimulation; the series as a whole may be ^' adaptive " in character (always adaptive from the Darwinian standpoint) or it may be wholly lacking in adaptiveness. Each element in the combination may be looked upon as a reflex. An instinct is thus a series of con- catenated reflexes. The order of the unfolding of the separate elements is a strictly heritable character. In- stincts are thus rightly said to be phylogenetic modes of DEFINITION OF REFLEX 107 response (as contrasted with habit, which is acquired dur- ing the lifetime of the individual). Such a series of re- flexes, or an instinct, is best illustrated by the young bird 's egress from the egg, and its later attempt at building a first nest; the first fighting responses in young animals, and in general the first attempts of young animals to capture, kill, and eat their prey. The act must be observed upon its first appearance if it is to be seen pure, i.e., without modification through habit.
Broader definition of the term reflex demanded. — If reflexes and instincts, by our definition, are to cover all forms of acquired movement not included under habit (p. 184) it is necessary to add that the term reflex should in- clude not only the more definite and fixed types of reflexes with which we are already familiar through our studies in physiology, but also those which are less constant, and less predictable (i.e., less predictable in the present state of our knowledge of the physical and chemical processes taking place in the organism). Jennings, Mast, Yerkes, and other American writers have shown that even the re- sponses of protozoa and the lower metazoa are not reflexes in the customary sense in which that term is used, i.e., in the sense of being absolutely fixed and wholly stereotyped forms of reaction. Every one wdll admit with Loeb that, given the same stimulus and the same organism, the re- action will be the same. Every one who attempts to work out a mechanical theory of life processes must admit this position, unless, along with his physico-chemical concepts, he is prepared to admit the possibility of the indeterminate action of entelechies and X-entities (see the work of Driesch and of Genung). But as a matter of observation we are not able in behavior, at present, to reduce all re- sponses to reflexes of this stereotyped kind. The organism is constantly changing. We may be able to control one element in the total system of stimulation of the animal at any given moment (e.g., the energy and wave-length of incident light) but we cannot control the internal physiological processes w^hich are also essential parts of the total stimulation and which also affect markedly the 108 STUDIES UPON INSTINCT state of the effector. The two factors, extra-organic stimu- lation and intra-organic stimulation, together determine the nature of the observable response. If either state changes, the overt response changes also; e.g., the Stentor may react in several different ways or in the same way but with a greater or less amplitude to the same (extra-organic) stimulus, provided the physiological state of the animal be different at the different moments of stimulation. In a similar way it may be shown that the so-called simple segmental reflexes in the higher forms of animal life are not unalterably fixed in character. Yerkes has shown that the amount of reflex movement of the leg of a frog called forth by an electric shock can be greatly increased by introducing an auditory stimulus simultaneously with the electric, although the auditory stimulus calls forth no ob- servable movement when given alone (see p. 388). Similar conditions hold in the case of the human knee jerk, and other reflex-like phenomena. The physiologist as a rule has investigated certain definite types of reflexes which are usually adaptive in character, such as the pupillomotor, those connected with respiration, circulation, the action of the glands and the muscles, etc. In general, while he looks upon these simple, direct types of response as calling, on the structural side, for the presence merely of an open pathway from receptor to effector (or from sensory surface to muscular mass where a nervous system is lacking), he knows, as has well been brought out by Sherrington, that there are many influences at work which alter the pervious-, ness of this pathway (blockage or the reverse at synapses, momentary or more lasting differences in the tonicity of the musculature, etc.), and thus alter the intensity and to some extent even the character of the so-called simple reflex. The simple reflex, then, even to the physiologist, as he ob- serves it in a spinal frog, is a general term to cover the more simple cases of segmental response. There is need, furthermore, to modify our notion of the reflex in still another direction. In reading genetic psychology, biology, and physiology, we are likely to be misled into thinking that all so-called reflex responses bear as definite and or- DEFINITION OF REFLEX 109 derly a character as do those of which we have just spoken; and that their adaptive value can be as easily caught sight of. If we look at any young animal at birth we cannot fail to be struck by the inchoate mass of muscular re- sponse, such as the random movements of hands and other motile organs of the body, the wrinkling of the facial muscles, etc. None of these movements is stereotyped and none is adaptive in the sense that it " puts the subject in the control of the stimulus," to use a phrase often quoted by the psychologist. It is rather interesting that the Dar- winian, who must find adaptive value in all instinctive activity, has not scrutinized random movement more care- fully. If we examine the congenital movements of the young of any species from birth until the instinctive equip- ment is complete, we find (1) that, while there is no quan- titative study at hand, mere observation shows that the number of random and unadaptive acts is far greater than is the number of organized adaptive reflexes and instinctive acts; (2) that under the influence of natural environmental demands or training many of these separate random acts can be organized into acts which are usually, but not necessarily, serviceable to the animal (habit formation, p. 184); and (3), finally, that many of them lie unorganized throughout the life history of the individual. In regard to this latter point it needs to be said that habit formation ceases after a time; the exigencies of en- vironment (or the stimulating factors in the environment) are not sufficient, as a rule, to call forth all of the latent possibilities of organization. These random and spon- taneous reflexes, unscrutinized by the physiologist,^the ceaseless movements of hands and arms, the facial mus- cles, and the turning and twisting of the trunk muscles and head as a whole, and later, climbing movements, run- ning, jumping, etc., — are of vital importance to the be- haviorist, in view of the fact that every habit which is later put on by the animal must inevitably be analyzable into just such units. What is new in habit is the organiza- tion. The elements, in general, are as old, or as new as the race.
110 STUDIES UPON INSTINCT Content of term reflex as used in behavior. — Reflex, then, as a unit of analysis of instinct (as also of habit, as a matter of fact, see p. 184), in the modified sense in which we use the term, embraces (1) the fairly definite and gen- erally predictable but unlearned responses of lower and higher organisms to stimuli. As examples of such acts among the invertebrates, we cite the responses of Euglena to the electric current, to gravity, to light, etc. These responses may consist of a definite movement towards or away from the stimulus. A characteristic but less general type of response of this kind is shown when Paramecium collides with objects: cilia are reversed, the animal swims backward, turning on the long axis of its body towards the aboral side; it then reverses the cilia again and starts in a new direction and repeats the above movements until forward movement can be continued without hindrance. Among the acts of vertebrates similar in definiteness and predictability we cite the reflexes of physiology such as the pupillar, plantar, patellar, etc. But we must be careful even in these cases not to over-emphasize the concept of invariability and predictability, since depending upon the physiological state of the organism we find, in extreme cases, the situation where a stimulus which at one time produces positive response may, under other conditions, produce negative response, e.g., when the frog is in a temperature of 10° it is positive to light, below 10°, nega- tive. (2) We have in the case of both vertebrates and invertebrates many examples of highly unstable and in- definite responses. The picture here is in part kaleidoscopic, neither the elements nor the grouping possibly being the same twice. In this class would fall the unadaptive and abortive types which have been more or less neglected: movements of head, trunk, etc., and in the undirected (i.e., so far as simple physical stimuli under the control of the investigator are concerned) movements of lower organ- isms. The latter can be illustrated by the ceaseless swim- ming movements of Paramecia, the loping walk of Amoeba, etc. These responses as a rule have been called ' ' random ' ' both in the literature on vertebrates and in that TYPES OF ACTIVITY 111 on invertebrates. It is evident, though, that the random movements when viewed en masse are congenital responses typical of the series. The random movements of the chick are quite different from those of the tern, and those of the Amoeba are different from those of the Paramecium. Turn- ing now to instincts which are made up of these reflex units, we should expect to find them at least as lacking in fixity as the units which compose them; and yet, just as there are many reflexes which, when examined in isolation, are found to be fairly permanent and stable so far as their qualitative features are concerned, just so do we find cer- tain consolidations of reflexes which are stable and as much a permanent possession of the animal as its arms and legs. Possibly the argument can be most readily advanced by examining some of the typical instincts of the higher ver- tebrates.
General types of instinct.^ — It is impossible, with the survey of animal activity which has been made, to give anything like a complete inventory of the various classes ^ On reaction types see Hamilton, op. cit., p. 62. In his study of mammals — human beings, monkeys, dogs, cats, and horses of dif- ferent ages — he finds five reaction types, A, B, C, D, E.
Type A. — This reaction must include a single definite effort to open each of three inferentially possible doors (for description of the method see p. 62 ), and must not include an effort to open the in- ferentially impossible door. It is called the rational inference type and is displayed only by adult normal human subjects.
Type B. — This tendency involves trying all four doors but in an irregular order: the unmodified searching tendency. It is ex- hibited by only defective human individuals and by all of the animals in the following order with respect to frequency of its display: mon- keys, dogs, cats, horses.
Type C. — Striking once each of the four doors in succession starting at either left or right: the tendency to adopt stereotyped modes of searching. This is especially exhibited by monkeys.
Type D. — This involves the error of making more than one sepa- rate continuous effort to open a given door during the same trial but always with an interruption of such repetitions of activity by an interval of effort to open some of the other doors: searching tend- ency modified hy recrudescent motor impulses. This tendency regu- larly increases as we descend the phyletic scale.
Type E. — This includes several modes of behavior which have a common objective characteristic, viz., automatism. It is a relative implastic unadaptive mode of behavior: the tendency tmvard per- severation of active impulses and inhihitions.
STUDIES UPON INSTINCT of instincts, or to give a classification which will be accepted by any large number of investigators. Nevertheless, we should expect to find, and indeed we do find, certain char- acteristic instincts in every species of vertebrates. If the animal has survived at all, it is necessary for it to have certain instincts which relate to food, shelter, reproduction, defense, and attack, etc. The table below may be found helpful in holding together the mass of material which one finds when examining the work of students of be- havior, and naturalists.
f Bodily characteristics by means of I. Structural characteristics, J which species are determined; methaction systems, etc.
ods of locomotion, such as creeping, t crawling, walking, etc.
II. Obtaining food.
' Taking food from beak of parent; sucking, pecking, scratching, diving; selection of food (when not deter- -( mined by habit, e.g., herbivorous, carnivorous, etc. ); the use of salt in- stead of fresh water; washing the ^ food; methods of drinking, etc.
III. Shelter.
Stretching the wing to escape the sun; sunning, huddling, ruffling the feathers when cold, etc.; burrowing, ^ taking up of abodes in hollow logs and trees; boring into timbers; hiberna- tion, etc. Overlaps to some extent the group on sex and food.
IV. Rest, sleep, play, etc.
Night and day periods of activity, purely instinctive, since no structural peculiarities account for the diiTer- -l ences; length of periods at nest, brooding or caring for the young; habits of sleep, i.e., bodily attitudes chosen; play; hibernation, etc.
V. Sex.
r Mating; copulation; nest site; ma- terial of nest; methods of building J nest; number of eggs laid or young cast; length of mating period or period in which partnership endures; care of the young, etc.
TYPES OF ACTIVITY VI. Defence and attack.
^ r Methods of attack, as lying on back; j springing upward (to head and I throat); spurring, goring with the antlers or horns, etc. Here belong also the hunting, stalking, seizing, and rending of live prey; shamming death; inflation of body; ejecting secretions, etc.
C Migration (possibly homing in genstinct.
VIII. Vocalization.
^ mals, fish, reptiles. Possibly over- I laps sex and food, but may be wholly t independent of either. Mimicry.
C Calls, cries, sounds uttered in receiv- I ing food; during sex activity, etc. -{ Shown in almost all vertebrate ] forms, but especially in the monkeys [ of the higher types and in birds.
IX. Unclassified and non- ( Strutting, dancing, inflation of cheek adaptive but complex •< pouches; secretion of musk; elab- and complete acts. ( orate nodding (as in the noddy tern).
X, Unclassified and non-adaptive, in f this case random and abortive, | sometimes appearing in one and J (Discussed under reflexes, tion, and sometimes in isola- } tion. t j' Reference is made here to very defi- nite phenomena but ones hard to de- scribe, such as persistence or the reverse in an attack on a problem (as shown in learning); boldness, individual tricks of hands, beak; ambidexterity or preponderating use of either right or left hand by any animal below man; probably heredi- tary but not known to be.
XI. Individual peculiarities in response.
As may be seen from this list, no attempt is made to produce a logical arrangement of instincts. This has been tried many times, but it is certainly impossible to get a classification at present based upon any other grounds than that of general convenience.
Methods of studying instinct. — Two general lines of attack upon instinct are open to us. The first method is 114 STUDIES UPON INSTINCT that of field observation. The work of the Peckhams on the social and solitary wasps, and that of Wheeler upon ants, serve both to show the working of the method and its general usefulness. Unfortunatel}^ there is no work on the study of the higher vertebrates comparable in completeness with those we have on the invertebrates. Instead, however, we have a series of publications more or less restricted in scope which deal with separate species of vertebrates. There is a fairly large number of more or less chance observations on mammals in captivity in the Avorks of Allen, Richardson, Slonaker, Small, Lashley, Watson, and Waugh; upon fish in the works of Bauer, Hess, Parker, Reighard, Romeis, Sheldon, Sumner, and others; upon birds in those of Craig, Strong, Herrick, Hess, and Porter; and upon reptiles and amphibia in those of Hess, Newman, Schaeffer, and Yerkes. Completely worked out, this method would give us the life-history or field activity of animals. The second method is that of isolating the animal and ob- serving the order of appearance of the instincts, measuring the degree of their perfectness, the progress towards per- fection through supplementation by habit, variations in their life-history, such as recurrency, waxing, waning, pos- sible loss through disuse, etc.
Various results obtained by the method of field ob- servation.— We can attempt to do no more here than illustrate a few of the more common instincts appearing in various representatives of the vertebrate phyla. In so far as possible we shall take one individual species and at- tempt to present a picture of its various modes of instinctive response. These responses are naturally given in their unanalyzed form, just as the animal exhibits them in its native habitat.
Instinctive activity of birds; the noddy tern.^ (I) The general bodily form, action systems, and taxo- nomic relations of the noddy tern need not concern us here. (II) On the first day after hatching the young bird strikes feebly its parent's beak. The movements are exceedingly poorly directed. Probably little food is ob- tained from the parent at first. Very rapidly the strength INSTINCTS OF THE NODDY TERN 115 of the stroke becomes greater and at the same time ability to open the beak increases commensurately. More and more food is obtained. Finally, at the end of fifteen to twenty days the young can take the food from the parent as rapidly as the latter can regurgitate it. In eight to ten weeks the young bird leaves the nest, and after wing practice, strikes out in search of food. Minnows of several different species are eaten exclusively. As the adult flies over the water its eyes meet schools of minnows hopping over the surface. It darts downward, seizes them in the beak, and swallows them. As the crop becomes filled it will often fly upward and swallow with extra force, giving a peculiar twisting spiral-like movement to the throat. As soon as the crop is well filled the bird goes to brood the egg or to feed the young; or if a male and no egg has been laid, to feed the female. The search for food is again taken up at intervals ranging from two to five hours. The method of drinking is characteristic. As the bird flies over the water it darts down and skims the surface with open beak. Often it darts down and Avets its breast feathers, especially on hot days when brooding the egg. Rarely, when soiled and possibly at other times, it dives completely undfir water. Occasionally it is found swimming in the water. (HI) In its typical habitat the noddy needs no shelter or extensive protection from the weather. "When young, the bird huddles under the wing of the parent, both to escape the cool wind.and rain and the too fierce rays of the sun. Even while young it shows a peculiar response which persists throughout life: when the sun is particularly warm it spreads out one wing fan-wise and remains standing for long periods of time Avith head di- rected always towards the wind. This response begins very early, at about eight to nine days. Sunning is another characteristic mode of response. The adult birds collect on the beach or house-tops AA^th head to wind, standing alAA^ays a fcAv inches apart. (IV) The bird is diurnal, sleeping apparently from dusk until daAA^n. Nothing is knoAAii of its sleeping attitudes. One bird occupies the nest at night while the other stands on a nearby limb. (The neighbor 116 STUDIES UPON INSTINCT of this bird, the sooty tern, apparently sleeps in short snatches during" the day and night. It is continually flying around the island at night, screaming and calling to mates and young. It has been nicknamed the " wide- awake tern.") The noddy, both after its turn to brood the egg and after obtaining food, often goes to a house-top, the shore, a stake, or a piece of driftwood, and stands motion- less for long periods of time. (A common response of terns, boobies, pelicans, etc.) (V) Nothing is known of the process of mating, since they reach the breeding ground apparently already mated. The choice of the nest site is a very simple matter; almost any place which will hold together a few sticks, seaweed, or shells may be chosen. Both animals (mates) work vigorously during the period of nest construction. Sometimes a very elaborate nest is built; at other times only a few sticks are thrown together on the ground or in the fork of some low bush. Often, as the animal brings in its single stick or shell, it will sit in the nest and turn round and round, thus giving the structure a characteristic shape. Quite frequently a half dozen shells and bits of seaweed are put in at the bottom of the com- pleted nest. The impulse to pick up straws persists for a long period of time, almost throughout the brooding period. During the period of active nest construction, both birds go out to feed. As soon as the nest is fairly well constructed the female sits on a nearby limb usually very close to the nest. She '' guards " this nest practically the whole day long, leaving only momentarily to drink. The male, on the other hand, goes out and fishes. On his return he bows elaborately to the female and she in turn begins to strike at his beak. If he has food in his crop he re- gurgitates it and the female eats from his bill. Only one egg is laid.. As soon as the egg is laid the instincts of the birds again change. Before the egg is laid the birds are timid and will fly up at the slightest disturbance. After the egg is laid the birds become exceedingly bold. They will fiercely attack the encroachments of any other bird and will even attack the human intruder. A laro^e number of the birds will actually sit on the nest and allow them- INSTINCTS OF THE NODDY TERN 117