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TYPES OF HUMAN BEHAVIOR

The human animal. Any attempt to understand what the nature of man is, apart from its training and education during the life of the individual, must start with the realization that man is a human animal. As a human being he is strikingly set off by his upright posture and his large and flexible hand. But chiefly he is distinguished by his plastic brain, upon which depends his capacity to perform the complex mental activities—from administering a railroad to solving problems in calculus—which constitute man's outstanding and exclusive characteristic.[1]

[Footnote 1: The thinking process is discussed in detail in chapters III and XIV.]

But in his structure and functions man bears, as is now well known, a marked resemblance to the lower animals. His respiratory and digestive organs, for example, may be duplicated as far down in the animal scale as birds and chickens.[2] Man's whole physical apparatus and mode of life, save in complexity and refinement of operations, are the same as those of any of the higher mammals. But more important for the student of human behavior, man's mental life—that is, his way of responding to and dealing with his environment—is in large part identical with that of the lower animals, especially of the most highly developed vertebrates, such as the monkey. They have, up to a certain point, precisely the same equipment for adjusting themselves to the conditions of life. Apart from education, both man and animal are endowed with a set of more or less fixed tendencies to respond in specific ways to specific stimuli. These inborn or congenital tendencies are generally known as reflexes or instincts.[1] These are unlearned ways, exhibited by both human and animal organisms, of responding promptly and precisely, and in a comparatively changeless manner to a given stimulus from the environment. These tendencies to act, while they may be, and most frequently are of advantage to the organism, are not conscious or acquired. They are irresistible impulses to do just such-and-such particular things in such-and-such particular ways when confronted with just such-and-such particular situations. In the well-known words of James:

[Footnote 2: With certain modifications accounted for in their historical "descent" with modification from a common ancestor. See Scott: Theory of Evolution.]

[Footnote 1: The difference between the two is largely one of complexity. By a reflex is meant a very simple and comparatively rigid response; by an instinct a series of reflexes such that when the first is set off, the remainder are set off in a regularly determinate succession.]

The cat runs after the mouse, runs or shows fight before the dog, avoids falling from walls and trees, shuns fire and water, etc., not because he has any notion either of life or death, or of self-preservation. He has probably attained to no one of these conceptions in such a way as to react definitely upon it. He acts in each case separately, and simply because he cannot help it; being so framed that when that particular running thing called a mouse appears in his field of vision he must pursue; that when that particular barking and obstreperous thing called a dog appears there he must retire, if at a distance, and scratch if close by; that he must withdraw his feet from water, and his face from flame.[2]

[Footnote 2: James: Psychology, vol. II, p. 384.]

Similarly, the baby's reaching for random objects, and sucking them when seized, its turning its head aside, when it has had enough food, its crying when alone and hungry, are not, for the most part, deliberate methods invented by the infant to maintain its own welfare, but are almost as automatic as the number of sounds omitted by the cuckoo clock at midnight.

Why do men always lie down, when they can, on soft beds rather than on hard floors? Why do they sit round the stove on a cold day? … Why does the maiden interest the youth so that everything about her seems more important and significant than anything else in the world? Nothing more can be said than that these are human ways, and that every creature likes its own ways, and takes to the following of them as a matter of course. … Not one man in a billion, when taking his dinner, thinks of utility. He eats because the food tastes good, and makes him want more. If you ask him why he should want to eat more of what tastes like that, instead of revering you as a philosopher, he will probably laugh at you for a fool.[1]

[Footnote 1: James: Psychology, vol. II, p. 386.]

These inborn tendencies to act vary in complexity from the withdrawing of a hand from a hot stove or the jerking of the knee when touched in a particular spot to startlingly involved trains of action to be found in the behavior of certain of the lower animals. Bergson cites the case of a species of wasp which with a skill, unconscious though it be, resembling that of the expert surgeon, paralyzes a caterpillar without killing it, and carries it home for food for its young.[2] There are again many cases of "insects which invariably lay their eggs in the only places where the grubs, when hatched, will find the food they need and can eat, or where the larvæ will be able to attach themselves as parasites to some host in a way that is necessary to their survival."[3] In many instances these complicated trains of action are performed by the animal in a situation absolutely strange to it, without its ever having seen the act performed before, having been born frequently after its parents had died, and itself destined to die long before its grubs will have hatched.

[Footnote 2: Bergson: Creative Evolution, p. 172.]

[Footnote 3: McDougall: Social Psychology, p. 24. (Except where otherwise noted, all references are to the fourth edition.)]

The number and variety of man's instincts. Various attempts have been made, notably by such men as James, McDougall, and Thorndike, to enumerate and classify the tendencies with which man is at birth endowed, or which, like the sex instinct, make their appearance at a certain stage in biological growth, regardless of the particular training to which the individual has been subjected. Earlier classifications were inclined to speak of instincts as very general and as half consciously purposeful in character. Thus it is still popularly customary to speak of the "instinct of self-preservation," the "instinct of hunger," and the "parental instinct." The tendency of present-day psychology is to note just what responses take place in given specific situations. As a result of such observation, particularly by such biologists as Watson and Jennings,[1] instincts have come to be regarded not as general and purposive but as specific and automatic. Thus it is no instinct of self-preservation that drives the child to blink its eyes at a blinding flash of light; it is solely and simply the very direct and immediate tendency to blink its eyes in just that way whenever such a phenomenon occurs. It is no deliberate intent to inhale the oxygen necessary to the sustenance of life that causes us to breathe. No more is it a conscious plan to provide the organism with nourishment that prompts us to eat our breakfast in the morning; it is simply the immediate and irresistible enticement of food after a night's fast. Not a deliberate motive of maternity prompts the mother to caress and care for her baby, but an inevitable and almost invincible tendency to "cuddle it when it cries, smile when it smiles, fondle it and coo to it in turn."

[Footnote 1: Watson: Behavior. H. S. Jennings: Behavior of the Lower Organisms.]

In the last few years, as a result of the observation of animals under laboratory conditions, there has been increasing evidence of a large number of specific tendencies to act in specific ways, in response to specific given stimuli. As no stimuli are ever quite alike, and no animal organism is ever in exactly the same physico-chemical condition at two different times, there are slight but negligible differences in response. Allowing for these, animals may be said to be equipped with a wide variety of tendencies to do precisely the same things under recurrent identical circumstances. The aim of the experimental psychologist is to discover just what actions occur when an animal is placed in any given circumstances, precisely as the chemist notes what reaction occurs when two chemicals are combined.

While experiments with the human infant are more difficult and rare (and while it is among infants alone among humans that original tendencies can be observed free from the modifications to which they are so soon subjected by training and environment) careful observers find in the human animal also a great number of these specific ways of acting. Just which of the large number of observed universal modes of behavior are original and unlearned, is a matter still in controversy among psychologists. There is practically complete agreement among them, however, with respect to such comparatively simple acts as grasping, reaching, putting things in the mouth, creeping, standing and walking, and the making of sounds more or less articulate. Most psychologists recognize even such highly complicated tendencies as man's restlessness in the absence of other people, his tendency to attract their attention when present, to be at once pitying and pugnacious, greedy and sympathetic, to take and to follow a lead.

In general, it may be said that man possesses not fewer instincts than animals, but more. His superiority consists in the fact that he has at once more tendencies to respond, and that in him these tendencies are more flexible and more susceptible of modification than those of animals. A chicken has at the start the advantage over the human; it can at first do more things and do them better. But it is the human baby who, though it cannot find food for itself at the start, can eventually be taught to distinguish between the nutritive values of food, secure food from remote sources, and make palatable food from materials which when raw are inedible.

An inventory and classification of man's original tendencies is made more difficult precisely because these are so easily modifiable and are, even in earliest childhood, seldom seen in their original and simple form.

At any given time a human being is being acted upon by a wide variety of competing and contemporaneous stimuli. In walking down a street with a friend, for example, one may be attracted by the array of bright colors, of flowers, jewelry and clothing in the shop windows, blink one's eyes in the glare of the sun, feel a satisfaction in the presence of other people and a loneliness for a particular friend, dodge before a passing automobile, be envious of its occupant, and smile benevolently at a passing child. It would be difficult in so complex and so characteristically familiar a situation to pick out completely and precisely the original human tendencies at work, and trace out all the modifications to which they have been subjected in the course of individual experience. For even single responses in the adult are not the same in quality or scope as they were to start with. Even the simplest stimuli of taste and of sound are different to the adult from what they are to the child. What for the adult is a printed page full of significance is for the baby a blur, or at most chaotic black marks on white paper.

But while it is difficult to disentangle out of even a simple, everyday occurrence the original unlearned human impulses at work, experimentation on both humans and animals seems clearly to establish that "in the same organism the same situation will always produce the same response." It also seems clear that in man these native unlearned responses to given stimuli are unusually numerous and unusually controllable. Upon the possibility of the ready modification of these original elements in man's behavior his whole education and social life depend.

Learning in animals and men. Men and animals are alike not only in that they have in common a large number of tendencies to respond in definite ways to definite stimuli, but that these responses may be modified, some strengthened through use, and others weakened or altogether discarded through disuse. In both also the survival and strengthening of some native tendencies, the weakening and even the complete elimination of others, depends primarily upon the satisfaction which flows from their practice.

It must be remembered that any situation, while it calls forth on the part of the organism a characteristic response, may also call out others, especially if the first response made fails to secure satisfaction, or if it places the animal in a positively annoying situation. There are certain situations—being fed when hungry, resting when weary, etc.—which are immediate and original satisfiers; there are others such as bitter tastes, being looked at with scorn by others, etc., which are natural annoyers. The first type the animal will try various means of attaining; the second, various means of avoiding. Through "trial and error," through going through every response it can make to a given situation, the animal or human hits upon some response which will secure for it satisfaction or rid it of a positive annoyance. Once this successful response is hit upon, it tends to be retained and becomes habitual in that situation, while other random responses are eliminated.

As will be pointed out in the following, man has developed in the process of reflection a much more effective and subtle mode of attaining desirable results, but a large part of human acquisition of skill, whether at the typewriter, the piano, the tennis court, or in dealing with other people, is still a matter of making every random response that the situation provokes until the appropriate and effective one is hit upon, and making this latter response more immediately upon repeated experiences in the same situation. Once this effective response becomes habitual it is just as automatic in character as if it had been made immediately the first time, and it is almost impossible without knowledge of the animal's or the human's earlier modes of response to detect the difference between an acquired response and one that is inborn.

This process of trial and error is perhaps best illustrated in the behavior of the lower animals where careful experiments have been conducted for the purpose of tracing the process of learning. In the classic cases reported by Thorndike and Watson, when chickens, rats, and cats were placed in situations where the first response failed to bring satisfaction, their behavior was in each case marked by the following features. At the first trial the animals in every case performed a wide variety of acts useless to secure the satisfaction they were instinctively seeking, whether it was food in a box, or freedom from confinement in a cage. Upon repeated trials the act appropriate to securing satisfaction was performed with increasing elimination of useless acts, and consequent decrease of the time required to perform the act requisite to secure food, or freedom, or both, as the case might be. One of Thorndike's famous cat experiments is best told in his own report:

If we take a box twenty by fifteen by twelve inches, replace its cover and front side by bars an inch apart, and make in this front side a door arranged so as to fall open when a wooden button inside is turned from a vertical to a horizontal position, we shall have means to observe such [learning by trial and error]. A kitten, three to six months old, if put in this box when hungry, a bit of fish being left outside, reacts as follows: It tries to squeeze through between the bars, claws at the bars, and at loose things in and out of the box, stretches its paws out between the bars, and bites at its confining walls. Some one of all these promiscuous clawings, squeezings, and bitings turns round the wooden button, and the kitten gains freedom and food. By repeating the experience again and again the animal gradually comes to omit all the useless clawings, and the like, and to manifest only the particular impulse (e.g., to claw hard at the top of the button with the paw or to push against one side of it with the nose) which has resulted successfully. It turns the button around without delay whenever put in the box. It has formed an association between the situation confined in a box with a certain appearance and the response of clawing at a certain part of that box in a certain definite way. Popularly speaking, it has learned to open a door by pressing a button. To the uninitiated observer the behavior of the six kittens that thus freed themselves from such a box would seem wonderful and quite unlike their ordinary accomplishments of finding their way to their food or beds. … A certain situation arouses, by virtue of accident or more often instinctive equipment, certain responses. One of these happens to be an act appropriate to secure freedom. It is stamped in in connection with that situation.[1]

[Footnote 1: Thorndike: Educational Psychology, Briefer Course. p. 129.]

Perhaps the most significant factor to be noted in this, and in similar cases, is that the successful response to a baffling situation is acquired, and that this acquisition remains a more or less permanent possession of the human or animal organism. Particularly important for the problem and practice of education is the mechanism by which these learned modes of behavior are acquired. For, to attain skill, knowledge, intellect, character, is to attain certain determinate habits of action, certain recurrent and stable ways of responding to a situation. The reason why the cat in the box ceased to perform the hundred and one random acts of clawing and biting, and after a number of trials got down to the immediately necessary business of turning the button was because it had learned that one thing only, out of the multitude of things it could do, would enable it to get out of the box and get its food. To say that it learned this is not to say that it consciously realized it; it means simply that when placed in such a situation again after having been placed in it a sufficient number of times, it will be set off to the turning of the button which gets it food, instead of biting bars and clawing at random—actions which merely serve further to frustrate its hunger. The animal has not consciously learned, but its nervous system has been mechanically directed.

A large part of the education of humans as well as of animals consists precisely in the modification of our original responses to situations by a trial-and-error discovery of ways of attaining satisfactory and avoiding annoying situations. Both animals and humans, when they have several times performed a certain act that brings satisfaction, tend, on the recurrence of a similar situation, to repeat that action immediately and to eliminate with successive repetitions almost all the other responses which are possible, but which are ineffective in the attainment of some specific satisfaction. The whole training imposed by civilization on the individual is based ultimately on this fundamental fact that human beings can be taught to modify their behavior, to change their original response to a situation in the light of the consequences that follow it. This means that while man's nature remains on the whole constant, its operations may be indefinitely varied by the results which follow the operation of any given instinct. The child has its original tendency to reach toward bright objects checked by the experience of putting its hand in the flame. Later his tendency to take all the food within reach may be checked by the looks of scorn which follow that manifestation of man's original greed, or the punishment and privation which are correlated with it. Through experience with punishment and reward, humans may be taught to do precisely the opposite of what would have been their original impulse in any given situation, just as the monkey reported by one experimenter may be taught to go to the top of his cage whenever a banana has been placed at the bottom.

The prolonged period of infancy. Probably the most significant and unique fact of human behavior is the period of "prolonged infancy" which is characteristic of human beings alone. Fiske and Butler in particular have stressed the importance of this human trait. In the lower animals the period of infancy—that is, the period during which the young are dependent upon their parents for food, care, and training—is very short, extending even in the highest form of ape to not more than three months. This would appear, at first blush, to be a great advantage possessed by the lower animals. They come into the world equipped with a variety of tendencies to act which, within a week, or, as in the case of chickens, almost immediately after birth, are perfectly adapted to secure for them food, shelter, and protection. They are mechanisms from the beginning perfectly adjusted to their environment.

The human infant, while it is born with a greater number of instinctive activities than other animals, is able to make little use of them just as they stand. For years after birth it is helplessly dependent on others to supply its most elementary needs. It must be fed, carried, and sheltered; it cannot by itself even reach for an object, and it cannot for nearly two years after birth specifically communicate its wants to other people. But this comparatively long helplessness of the human infant is perhaps the chief source of human progress.

The human baby, because it can do so little at the start, because it has so many tendencies to act and has them all so plastic, undeveloped, and modifiable, has to a unique degree the capacity to learn. This means that it can profit by the experience of others and adjust itself to a great variety and complexity of situations. The chicken or the bird can do a limited number of things perfectly, but it is as if it had a number of special keys opening special locks. The power of modifying these instinctive adjustments, the capacity of learning, is like being put in possession of a pass-key. As Professor Dewey puts it, "An original specialized power of adjustment secures immediate efficiency, but, like a railway ticket, it is good for one route only. A being who, in order to use his eyes, ears, hands, and legs, has to experiment in making varied combinations of their reactions, achieves a control that is flexible and varied."[1]

[Footnote 1: Dewey; Democracy and Education, p. 53.]

The more complex the environment is in which the individual must live, the longer is the period of infancy needed in which the necessary habits and capacities may be acquired. In the human being the period of infancy extends in a literal sense through the first five years of the individual's life. But in civilized societies it extends factually much longer. By the end of the first five years the child's physical infancy is over. It can take care of itself so far as actually feeding itself, moving about, and communicating with others is concerned. But so complex are the habits to which it must become accustomed in our civilization that it is dependent for a much longer period. The whole duration of the child's education is a prolongation of the period of infancy. In most civilized countries, until at least the age of twelve, the child is literally dependent on its parents. And with every advance in civilization has come a lengthening in the period of education, or learning.

Intellectually, the period of infancy might be said not really to be over before the age of twenty-five, by which time habits of mind have become fairly well fixed. The brain and the nervous system remain fairly plastic up to that time, and if inquiry and learning have themselves become habitual, plasticity may last even longer. In the cases of the greatest intellects, of a Darwin, or a Newton, one might almost say the period of infancy lasts to old age. To be still learning at sixty is to be still a child in the best sense of the word. It is still to be open rather than rigid, still to be profiting by experience.

The great social advantages of the prolonged period of infancy lie in the fact that there is a unique opportunity both for the acquisition by individuals and for the imposition on the part of society of a large number of habits of great social value. The human being, born into a world where there are many things to be learned both of natural law and human relations, is, as it were, fortunately born ignorant. He has instincts which are pliable enough to be modified into habits, and in consequence socially useful habits can be deliberately inculcated in the immature members of a society by their elders. The whole process of education is a utilization of man's prolonged period of infancy, for the deliberate acquisition of habits. This is all the more important since only by such habit formation during the long period of human infancy can the achievements of civilization be handed down from generation to generation. Art, science, industrial methods, social customs, these are not inherited by the individual as are the instincts of sex, pugnacity, etc. They are preserved only because they can be taught as habits to those beings who come into the world with a plastic equipment of instincts which lend themselves for a long time to modification.

Consciousness of self and reaction to ideas. A significant difference between the actions of human beings and those of animals is that human beings are conscious of themselves as agents. They may be said not only to be the only creatures who know what they are doing, but the only ones who realize their individuality in doing it. Dogs and cats are not, so far as we can draw inferences from extended observation of even their most complex actions, conscious of themselves. It is not very long, however, before the human animal begins to set itself off against the remainder of the universe, to discover that it is something different from the chairs, tables, and surrounding people and faces that at first constitute for it only a "blooming, buzzing confusion." A human being performs actions with a feeling of awareness; he is conscious of himself. This consciousness of self (see chapters VII and VIII) becomes more acute as the individual grows older. It has consequences of the gravest character in social, political, and economic life. It is a large factor at once in such different qualities of character as ambition, friendship, humility, and self-sacrifice, and is responsible in large measure for whatever truth there is in the familiarly spoken-of conflict between "the individual and society."

Human beings are, furthermore, susceptible to a unique stimulation to action, namely, ideas. Animals respond to things only, that is, to things in gross:

It may be questioned whether a dog sees a rainbow any more than he apprehends the political constitution of the country in which he lives. The same principle applies to the kennel in which he sleeps and the meat that he eats. When he is sleepy, he goes to the kennel; when he is hungry, he is excited by the smell and color of meat; beyond this, in what sense does he see an object? Certainly he does not see a house—i.e., a thing with all the properties and relations of a permanent residence, unless he is capable of making what is present a uniform sign of what is absent—unless he is capable of thought.[1]

[Footnote 1: Dewey: How We Think, p. 17.]

Human beings can respond to objects as signs of other things, and, what is perhaps more important, can abstract from those gross total objects certain qualities, features, elements, which are universally associated with certain consequences. They can respond to the meaning or bearing of an object; they can respond to ideas.

To respond to ideas means to respond to significant similarities in objects and also to significant differences. It means to note certain qualities that objects have in common, and to classify these common qualities and their consequences in the behavior of objects. To note similarities and differences in the behavior of objects is to enable individuals to act in the light of the future. The printing on this page would be to a dog or to a baby merely a blur. To the reader the black imprints are signs or symbols. To the animal a red lantern is a haze of light; to a locomotive engineer it is a sign to halt. To respond to ideas is thus to act in the light of a future. It makes possible acting in the light of the consequences that can be foreseen. Present objects or features of objects are responded to as signs of future or absent opportunities or dangers. Every time we read a letter, or act in response to something somebody has told us, we are responding not to physical stimuli as such, but to those stimuli as signs of other things.

Human beings alone possess language. The value of the period of infancy in the acquisition of habits and the unique ability of human beings to respond to ideas is inseparably connected with the fact that man alone possesses a language, both oral and written. That is to say, men alone have an instrument whereby to communicate to each other feelings, attitudes, ideas, information. To a very limited degree, of course, animals have vocal and gesture habits; specific cries of hunger, of sex desire, or distress. But they cannot, with their limited number of vocal mechanisms, possibly develop language habits, develop a system of sounds associated with definite actions and capable of controlling actions. Only human beings can produce even the simplest system of written symbols, by which visual stimuli become symbols of actions, objects, emotions, or ideas. Biologists—in particular the experimentalist, Watson—find, in the capacity for language, man's most important distinction from the brute.

Language may be said, in fact, to be the most indispensable instrument of civilization. It is the means whereby the whole life of the past has been handed to us in the present. It is the means whereby we in turn record, preserve, and transmit our science, our industrial methods, our laws, our customs. If human relations were possible at all without a language, they would have to begin anew, without any cultural inheritance, in each generation. Education, the transmitter of the achievements of the mature generation to the one maturing, is dependent on this unique human capacity to make seen marks and heard sounds stand for other things. The extent to which civilization may advance is contingent upon the development of adequate language habits. And human beings have perfected a language sufficiently complicated to communicate in precise and permanent form their discoveries of the complex relations between things and between men.

Man the only maker and user of tools. One of the most important ways in which man is distinguished from the lower animals is in his manufacture and use of tools. So far as we know the ability to manufacture and understand the use of tools is possessed by man alone. "Monkeys may be taught a few simple operations with tools, such as cracking nuts with a stone, but usually they merely mimic a man."[1] Man's uniqueness as the exclusive maker and user of tools is made possible by two things. The first is his hand, which with its four fingers and a thumb, as contrasted with the monkey's five fingers, enables him to pick up objects. The second is his capacity for reflection, presently to be discussed, which enables him to foresee the consequences of the things he does.

[Footnote 1: Mills: The Realities of Modern Science, p. 1.]

The use of tools of increasing refinement and complexity is the chief method by which man has progressed from the life of the cave man to the complicated industrial civilization of to-day. Bergson writes in this connection:

As regards human intelligence, it has not been sufficiently noted that mechanical invention has been from the first its essential feature, that even to-day our social life gravitates around the manufacture and use of artificial instruments, that the inventions which strew the road of progress have also traced its direction. This we hardly realize, because it takes us longer to change ourselves than to change our tools. Our individual and even social habits survive a good while the circumstances for which they were made, so that the ultimate effects of an invention are not observed until its novelty is already out of sight. A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us. But the revolution it has effected in industry has nevertheless upset human relations altogether. New ideas are arising, new feelings are on the way to flower. In thousands of years, when, seen from the distance, only the broad lines of the present age will still be visible, our wars and our revolutions will count for little, even supposing they are remembered at all; but the steam engine and the procession of inventions that accompanied it, will perhaps be spoken of as we speak of the bronze or of the chipped stone of prehistoric times: it will serve to define an age. If we could rid ourselves of all pride, if, to define our species, we kept strictly to what the historic and the prehistoric periods show us to be the constant characteristic of man and of intelligence, we should not say Homo sapiens, but Homo faber.[1]

[Footnote 1: Bergson: Creative Evolution, pp. 138–39.]

Man's intelligence, it has so often been said, enables him to control Nature, but his intelligence in the control of natural resources is dependent for effectiveness on adequate material instruments. One may subscribe, though with qualification, to Bergson's further statement, that "intelligence, considered in what seems to be its original feature, is the faculty of manufacturing artificial objects, especially tools to make tools, and of indefinitely varying the manufacture."

Anthropologists distinguish the prehistoric epochs, by such terms as the Stone, Copper or Bronze, and Iron Ages, meaning thereby to indicate what progress man had made in the utilization of the natural resources about him. We date the remote periods of mankind chiefly by the mementos we have of the kinds of tools they used and the methods they had developed in the control of their environment. The knowledge of how to start and maintain a fire has been set down as the practical beginning of civilization. Certainly next in importance was the invention of the simplest tools. There came in succession, though æons apart, the use of chipped stone implements, bronze or copper instruments, and instruments made of iron. In the ancient world we find the invention of such simple machines as the pulley, the use of rope, and the inclined plane.

Without tracing the history of invention, it will suffice for our purpose to point out that agriculture and industry, men's modes of exploiting Nature, are dependent intimately on the effectiveness of the tools at their disposal. It is a far cry from the flint hatchet to the McCormick reaper and the modern steel works, but these are two ends of the same process, that process which distinguishes man from all other animals, and makes human civilization possible: that is, the use and the manufacture of tools.