SUMMARY 181 established. The hen, after ovariotomy, assumes the spurs and plumage of the male. The crab, castrated by the para- sites, Sacculina, assumes the proportions and many of the characteristics of the female. Cunningham supposes that such observations prove that the development of the sec- ondary sexual characters follows upon the production of some secretion of the reproductive cells or gonads. He then assumes that a reversal of the process is possible, i.e., that a developing structure, a callus, e.g., can produce a secretion or hormone, which, carried in the blood, may reach the reproductive cells and induce in them a change corresponding to the somatic change. Since Cunningham published the theory (1908), a considerable body of favor- able evidence has been collected. (As examples, see the works of Gudernatsch, Todd, Rorig.-) Summary. — Since, finally, the activities of organisms must be considered as the functioning of definite structural elements, the problem of the origin of new reflexes, of new instincts, and of new possibilities of habit formation become one with the problem of the evolution of morphological characters in general. In the instinct, as in the structural arrangements, tw^o orders of phenomena are apparent — diversity and fitness. The diversity is accounted for by the interaction of developmental processes within the organism, and environmental factors. Most of the variations in the individual are quite undirected and without adaptive rela- tion to the agents producing them, but some, like the new characters acquired in habit formation, are made adaptive by a process of learning in the individual. The inheritance of such adaptive characters, if demonstrated, would form a ready method of evolution which would account for all diversity and fitness; but as yet the inheritance of somatic adaptation is not established. The only new characters whose heritability has been demonstrated are mutations, and these are never directly adaptive. The problem as to why ^ The " Mneme " of Semon in which an attempt is made to ex- plain the inheritance of acquired characters can scarcely be inter- preted in terms of a physiological mechanism and is of little help in the envisagement of our problems.
182 CONCERNING THE ORIGIN OF INSTINCTS they seem to be adaptive is answered — how completely it is as yet uncertain — by assuming that natural selection elimi- nates individuals (mutants) which are not endowed with characters enabling it to exist in the locality in which it first appears. The application of either the selection or the direct adaptation theory to behavior complexes is as yet impossible, owing to the lack of any very definite concepts of the structural basis of behavior.
BIBLIOGRAPHY Bateson, W., Mendel's Principles of Heredity. Cambridge, 1909.
Problems of Genetics. New York, 1913.
Cesnola, a. p., " Preliminary Note on the Protective Value of Color in Mantis Religiosa," Biometrica, 1904, 3.
Chauvin, Marie V., " Ueber die Verwandlung der mexieanischen Axolotl in Amblystoma," Zeit. f. wiss. ZooL, 1876, XXVII, 522.
Cunningham, J. T., " An Experiment Concerning the Absence of Color from the Lower Sides of Fiat-Fishes," Zool. Anz., 1891, " The Heredity of Secondary Sexual Characters in Relation to Hormones, a Theory of the Heredity of Somatogenic Characters," Arch. f. Entw., 1908, 26.
Dakwin, Chas., Origin of Species. London, 1875, sixth edition.
Davenport, C. B., " Light Thrown by the Experimental Study of Heredity upon the Factors and Methods of Evolution," Amer.
De Vries, Hugo, Species and Varieties; Their Origin hy Mutation. Chicago, 1905.
FULD, E., " Ueber Veranderungen der Hinterbeinknochen von Hun- den." Arch. f. Entiv., 1901.
GoLDFARB, A. J., " The Influence of the Nervous System in Regenera- tion," Jour. Exp. Zool., 1909, 7.
GuDERNATSCH, J. F., " Feeding Experiments on Tadpoles," Arch. f.
JoHANNSEN, W., Ucler Erhlichkeit in Populationen und in reinen Kammerer, Paul, " Experimentelle Fortpfianzungsveranderung bei Geburtshelferkrote {Alytes ohstetricans) u. Laubfrosch (Hyla arhorea)," Arch. f. Entw., 1906, 22.
" Vererbung erzwungener Fortpflanzungsanpassungen.
III. Die Nachkommen der nicht brutpflegenden Alytes ohstet- "Das Farbkleid des Feuersalamanders (Salamandra maculosa Laurenti) in seiner Abhangigkeit von der Umwelt,' Lamarck, Philosophic Zoologique. Paris, edition of Charles Mar- MacDougal, D. T., "Alterations in Heredity Produced by Ovarial Treatment," Bot. Gazette, 1911, 51.
BIBLIOGRAPHY 183 Mayer, A, G., "Mating Instincts in Moths," Ann. Mag. Nat. Hist., Mayer, A. G., and Soule, C. G., " Some Keactions of Caterpillars and Moths," Jour. Exp. Zool., 1906, 3.
Mendel, G. J., Versuche iiber Pfianzen-Hyhriden, (English transla- tion reprinted in Bateson's Principles of Heredity).
Morgan, T. H., Heredity and Sex. New York, 1913.
Parker, G. H., "Adaptation in Animal Reactions," Amer. Nat., Pearl, Raymond, " Data on the Relative Conspicuousness of Barred and Self-Colored Fowls," Amer. Nat., 1911, 45.
" Notes on the Sex Behavior of the Poitou Jacks," PouLTON, E. B., and Saunders, C. B., An Experimental Inquiry into the Struggle for Existence in Certain Common Insects, Bristol, Report, British Asso., 1898. Przibram, Hans, Phylogenese. Leipzig, 1910.
Reighard, Jacob, "An Experimental Study of Warning Colora- tion in Coral-Reef Fishes." Washington, Papers from Tortugas Lab. of Carnegie Inst., 1908, 2. Rommel, G. M., " The Grevy Zebra as a Domestic Animal," Amer.
Breeders' Mag., 1913, IV, 3. Schroeder, C, " Ueber experimentell erzielte Instinktvariationen," Verh. d. Deutsch Zool. Ges., 1903. Semon, R. N., Die Mneme als erhaltendes Prinzip im WecJisel des organischen Geschehens. Leipzig, 1908. Spemann, H., " Ueber die Entwicklung umgedrehter Hirnteile bei Amphibienembryonen," Zool. Jahrh., 1912, 3 (Supp. 15). Stockard, C. R., " The Artificial Production of a Single Median Cyclopean Eye in the Fish Embryo," Arch. f. Entw., 1907, 23. Todd, Chas., " On the Recognition of the Individual by Hgemolytic Methods," Jour. Genetics, 1913, 3. Tower, W, L., Evolution in Chrysomelid Beetles of the Genus Leptinotarsa. Washington, Carnegie Pub., 1906. Yerkes, R, M., The Dancing Mouse. New York, 1907.
" The Heredity of Savageness and Wildness in Rats," Jour. Animal Beh., 1913, III, 286.
CHAPTER VI THE EXPERIMENTAL STUDY OF HABIT FORI^IATION I. Content of term habit. — Restatement. II. Types of habit. — ^Motor habits; mammals. — Motor habits; birds. — Motor habits; fish. — Motor habits; reptiles. — ^Habits of manipulation; mammals. — Habits of manipulation; birds. — Sensory habits. III. Curves of learning; motor habits. — Curves of learning; sensory habits, — Motor habits in human beings. — Comparative learning ability of different animals. IV. The rise of habits when incentives are controlled. — Habits formed without the use of punishment, — With punishment as the sole incentive. — With punishment for wrong response and food for right response. V. Analysis of reflexes involved in habit. — Normal and operative methods of eliminating sensory impulses, — Some results of experimental analysis of motor habits in mammals, — Analysis of motor habits in birds. — ^Analysis of sensory habits in mammals, — ^Analysis of the delayed reaction in mammals, — Summary. VI, Efficiency of training methods: motor habits. — Sensory habits. — The de- layed reaction. VII. Other conditions which affect learn- ing.— (1) Age. — (2) Sex. — (3) Certain bodily conditions. — (4) Learning in animals with less than normal brain weights, — Motor habits in animals with parts of nervous system removed. VIII. Effect of previous habits upon the formation of new habits: motor habits. IX. Retention. — ^Mammals. — Birds. — Amphibia and reptiles.
I. Content of the term habit. — In Chapter IV it was shown that instinct is analyzable into simple congenital re- flexes. It was suggested there that habit also might, so far as analysis goes, be found to consist of congenital reflexes. Experimental studies upon habit formation lend support to this view. Instinct and habit differ so far as concerns the origin of the pattern (number and localization of simple reflex arcs involved) and the order (temporal relations) of the unfolding of the elements composing that pattern. In instinct both pattern and order are inherited: in habit both are acquired. We do not hesitate to define habit as we do instinct — as a complex system of reflexes which CONTENT OF TERM HABIT 185 function in a serial order when the organism is confronted by certain stimuli, provided we add the clause which marks off habit from instinct, viz., that in habit the order and pattern are acquired during the life of the individual ani- mal. After habits are perfected they function in all par- ticulars as do instincts. No mere examination of adult animals will enable us to differentiate between the respec- tive roles of habit and instinct, since the one observable difference between the two types of acts is that of origin. Since habits are thus seen to be individual acquisitions of particular animals, it is necessary to describe the process by means of which certain reflexes are selected out from among a very large number of possible reflexes. Such a description of the factors involved in selection can be more adequately presented after we have looked more carefully into some of the general features of habit. Accordingly we shall take up the process of selection in the following chapter.^ It may be inferred from the above statements ^ We must emphasize the fact that all organized responses which can be called forth from both man and animal fall under the one or the other of these heads, instincts (including here the simplest form of reflexes), and habits. In Chapter I we tried to show that what are called "images" (and the thought processes generally) are really nothing more than the implicit habits which are formed principally in the laryngeal muscles, and we would further state now that those functions which we have hitherto called " affective " really belong in the realm of instincts. It will be remembered that James made the following distinction between the motor processes of emotions and those of instincts: those underlying emotions con- sist of bodily reverberations, movements of breathing, circulation, glands, etc., the loci of which are confined to the subject's own body; whereas those underlying instincts consist largely of movements of the striated muscles. As we understand James he seemingly would make emotions objects of introspection, whereas instincts are the legitimate prey of the behaviorist. Since we do not admit any such distinction, it follows that from our point of view both emo- tions and instincts belong in one and the same class. It follows further that the so-called affective processes must be grouped under what has hitherto been called emotions, and hence under our gen- eral class of instinctive modes of response. Behavior regards all three groups from the same point of view. A given stimulus may, through inherited systems of reflexes, produce a response of a cer- tain kind in the striped musculature which we may name flight. On the other hand a stimulus may produce its effect largely through the sympathetic system '(dilation of vessels in the face, etc.) which psychology would call embarrassment, finally (as a special form of 186 STUDY OF HABIT FORMATION that the organism is dependent upon heredity for unit acts. The number of these apparently can never be increased or decreased, but large numbers of them can be shaped so as to form different types of habit, depending upon the kind of environment into which the organism is thrown. The organism is so constructed that when certain stimuli are presented certain types of random movements are set free. Individuals certainly differ enormously in the number and kinds of random activity which they may display upon the presentation of given stimuli.^ If ap- propriate random acts do not appear upon the incidence of the given stimulus, it is fruitless to attempt to establish habits respecting that stimulus, e.g., if the child fails to respond adequately to colors, pencils, chalk, and to the form and size of objects (Avhen intensity and combination are sufficiently varied) it is useless to try to instil artistic habits. On the other hand, this same child may show a rich display of random activity, suitable to the formation of habit, when presented with the objects belonging to what are called the mechanical arts or trades; habits under such conditions are formed quickly and readily. It seems safe to conclude that all of the vocations are probably at bottom dependent upon particular hereditary types of or- ganization, i.e., dependent upon the presence of ran- dom activity of proper kinds. The same thing appears in the case of the animals. It has long been recognized that in order to get the animal to form habits one must set problems for him which will call only for the random type of activity of which he is capable. One does not usually set the same type of problem for a bird that one sets for a monkey. We scrutinize pretty carefully in the young animal the reperemotion) another stimulus, through inherited or acquired connec- tions, may produce an effect of one or another kind upon the errogenous zones, which psychology would class as the one or the other affective element (process?).
2 It would be interesting to test habit formation under conditions such that instead of increasing the stimulating value of an object (complex stimuli) we should heighten the state of irritability of the organism by the administration of strychnine, etc. The effect of drugs on behavior can be more easily attacked in the animal than in the human world.
RESTATEMENT 187 toire of random activity, and so shape the problems that their solution calls for no unit acts not in his repertoire.
Restatement. — What we emphasize in brief may be stated again: when an animal is presented with a stimulus which calls forth random movements (e.g., food inside of a problem box), the reflex repertoire is set free. Now in this repertoire is a combination of reflexes which will en- able the animal to get food. In some way (by a purely mechanical process, to be later described) this combination gets selected and in time comes to be the only system which responds when that particular object is presented to the animal. It should be clear from our description that to use the term '^ habit " to cover all observable adjust- ment in animals is most confusing. The literature is full of such titles as the " habits and natural history " of a given species. Such titles cover both the instincts and the habits of the animals under consideration, and no effort is made to separate the two forms of adjustment. A still more violent strain upon the meaning which the term habit should connote comes from experimental zoology. They speak there of the habits of growth of certain tissues. In such cases it is preferable to speak of temporally spaced systems of growth, or to adopt some wholly new phrase. The term habit should be confined strictly to new forms of adjustme^it acquired during the lifetime of the indi- vidual animal.^ II. Types of habit. — The human experimenter in the laboratory forces certain types of habit upon particular animals. Where the object is to bring into relief the va- rious action systems, he forces the animals to form what are called motor habits. In studying them the experimenter may be primarily interested in the rapidity of the forma- tion of such habits; the stages in their formation, such as the initial accuracy of the first performance, when con- sidered from the standpoint of the amount of excess time and excess effort'; the rate of elimination of these excess ^ It is just possible that owing to the growing body of evidence that certain habits are transmitted by parent to offspring, we shall have to speak of ontogenetic habits and phylogenetic habits.
188 STUDY OF HABIT FORMATION factors in early stages and in later stages; the number and complexity of the habits which may be formed; whether such habit systems mutually influence one another as regards reenforcement or the reverse. He may wish to consider, after having determined the normal course of the formation of a habit, ways in which the so-called normal process may be altered, e.g., the effect of " putting the animal through " the act, allowing the trained animals to perform within the sensory range of the untrained ani- mals, etc. We shall reserve the discussion of these latter factors until Chapter VIII is reached.
Examination of the work which has been done on motor habits shows that such habits fall usually under two sub- heads: (1) motor habits in the narrow sense, e.g., as those formed in the maze and in box I; and (2) habits of manipu- lation, e.g., the opening of latches, the pulling of strings, turning buttons, pulling out plugs, etc. Such acts may be very simple or, through combination, very complex. In the discussion which follows we use the term motor habit in its restricted sense.
In contrast to the motor stand the sensory habits (called by Yerkes discrimination habits). Here emphasis is laid upon the functioning of the receptor (or upon defining the stimulus to which response is made, p. 61) rather than upon that of the muscle. The act which the animal has to perform may be already in its repertoire, e.g., he may have only to walk to the right or to the left, depending on which side the stimulus is administered. The experi- menter's object is to bring out the whole range of stimuli to which the animal can respond, the amount of stimula- tion necessary for response, etc. His criterion, however, as to whether the stimulus lies within the sensory range of the animal is afforded by the fact that a definite habit can be formed, viz., that of reacting positively or negatively to the stimulus. The results presented in the chapters on sensory responses have been largely obtained by forcing the formation of such habits. On p. 220 we shall undertake the analysis of a group of sensory habits (the response of rodents to monochromatic lights).
TYPES OF HABIT 189 A third type of habit of very great interest has been studied at the University of Chicago, mainly under the influence of H. A. Carr. This type of habit, called the delayed response,^ falls under neither of the above heads, yet it seems to involve very complex motor processes as well as sensory. The essential object in establishing the delayed reaction is (1) to see within what limits reaction to a given stimulus may be delayed. In a rough way we might illustrate the type of delayed reaction by citing those cases of hunting animals which prey upon smaller species living in holes or coverts. The hunter is stimulated visually only momentarily by his prey; nevertheless, he goes to the place into which it has vanished. He is react- ing during the final stages of the response just as though the specific visual stimulus were present.^ This response has been brought under laboratory control by training the animal to go for food to a light which may appear in any one of three boxes, left, in front, or to the right (for ap- paratus see p. 105). After training, the light is turned on in any one of the boxes. While the light is on the animal is stimulated by it but he is restrained from reacting to it. The light is then turned off. The experimenter waits for a definite interval and then releases the animal. The correct response on the animal 's part calls for a positive movement towards the box in which the light has appeared. (2) Another object of the experimenter is to determine the factors by means of which correct response is attained (i.e., the behavior during the period of delay, maintenance of bodily attitude, etc.).
Motor habits: mammals. — One can very easily watch the * The element of delay is present probably in every habit. It is possible to consider this form of response under the heading of kinsesthetic and organic responses (p. 421). On the whole, how- ever, it seems more appropriate to treat it under the general head of habit.
^ Those familiar with the work on the lower organisms will recognize at once the fact that in this type of habit one meets the old question in somewhat different form as to whether the stimulus to orientation must exert its directive influence constantly as is assumed by Loeb for the tropism, or discretely and momentarily as is maintained by Jennings and Mast.
190 STUDY OF HABIT FORMATION formation of a motor habit by allowing the white rat to obtain food from a simple problem box, such as that shown in box I on p. 94. We have reason to believe, through our knowledge of the rat's motor organization, before we start, that the acts by means of which he will get the food all lie within his repertoire. After sawdust has been banked around the box for a height of 2 or 3 inches the food is placed inside. Since there is no instinctive mechanism which will immediately enable the animal to get the food, several separate reflexes must be chained together. These, when perfectly concatenated, will function just as surely and just as perfectly as an instinct. This fact must be emphasized — the physiological condition of the animal is such (state of hunger) that food stimuli (it will be seen that we cannot tell what receptors are involved, smell, sight, etc., except by experimental analysis) will release the native reflexes. In this case they are, in brief, as follows: Eunning rapidly and walking slowly from place to place; sniffing, sneezing, washing the face or body; touching constantly the sides of the restraining cage and the box with vibrissse or the bare snout, feet, etc.; clinging to all of the objects, sometimes with head up and sometimes with head down; crawling on the ceiling of the restraining cage; butting the nose into the crevices of the wire; gnawing at the wire and at all of the wooden parts; pushing with great force against the box; stopping every few minutes to clean the paws of bits of sawdust; sitting up on haunches and chewing these bits; scratching at the sawdust with a group of characteristic m^ovements which not only produce a hole but throw out the sawdust as well (this of course when the animal has had no experience with the sawdust); squeezing through holes so made; moving vibrissas and nose across the bottom of the cage; mounting up through the hole; seizing the food; dragging it out to the nest, in case the latter is allowed, etc. This list is not by any means complete. These movements are repeated over and over again with ever varying order. Finally, however, the order is such that the food is obtained. The animal walks to a definite place, scratches and pushes out the sawdust MOTOR HABITS IN BIRDS 191 to make a hole sufficiently large to squeeze through, enters and reaches the food. The total time of success will vary (7.04 min. — 17.65 min.). On the second trial, which may be given immediately after the first (but the time of suc- cess of the second trial will vary with the method) we find, as a rule, an enormous decrease in the number of reflexes. The activity is more confined, i.e., the area covered by the animal is less and what area is covered is covered less intensively (time, 1.69 min. — 7.20 min.). On the third trial the time is still further decreased (.48 min.). At the fourteenth trial the time is reduced to.11 min.
Motor habits: birds. — A similar motor habit in birds follows: When a wire box with a suitable door has been inverted over the nest of a sooty tern and left there until the bird has become completely accustomed to it, and the opening is then banked up with sand, we observe somewhat similar movements to those just de- scribed in the case of the rat. On the first test the bird alighted from the air near the nest. It did not seem frightened by the change in conditions. It walked imme- diately to the nest, but finding the sand, walked around and around the box trying to force its way in through the meshes of the wire. It tried to get into the door again, but would not scratch at the sand. It divided its time between the east side of the box where the eggs could be plainly seen, and the west side where it had formerly gained ad- mission. The types of movement displayed were, on the whole, rather simple: they consisted mainly of walking; pushing the beak through the meshes of the wire, striking the wings against the cage, flying away for a short dis- tance and then coming back to the old alighting place, only to repeat the endless movements just described. It is rather interesting to note that the bird did not use the scratching reflex, although this particular species digs a hole in the sand in which to deposit its eggs. This reflex seems to be tied up with a very definite period of the nesting cycle, viz., such holes are dug only before the egg is laid. Nevertheless it is possible to exaggerate the inflexibility of this reflex, since even the young birds will dig holes in