According to the evidence of those scientists who have studied the remains of animals found in the earth's crust, there is a gradual development of animal forms shown in successive epochs. In the very oldest parts of the earth's crust, the remains of animal life found are very simple. In later formations, the remains show an animal life more complex. The highest forms of animals, the mammals, are found only in the more recent formations. The remains of man are found only in the latest formations.

Putting these two facts together--(1) that the higher types of mind are found to-day only in the higher types of animals, and (2) that a gradual development of animal forms is shown by the remains in the earth's crust--the conclusion is forced upon us that mind has pa.s.sed through many stages of development from the appearance of life upon the earth to the present time. Among the lower forms of animals to-day one sees evidence of very simple minds. In amoebas, worms, insects, and fishes, mind is very simple. In birds, it is higher. In mammals, it is higher still. Among the highest mammals below man, we see manifestations of mind somewhat like our own. These grades of mentality shown in the animals of to-day represent the steps in the development of mind in the animals of the past.

We cannot here go into the proof of the doctrine of development. For this proof, the reader must be referred to zoology. One further point, however, may be noted. If it is difficult for the reader to conceive of the development of mind on the earth similar to the development of animals in the past, let him think of the development of mind in the individual. There can certainly be no doubt of the development of mind in an individual human being. The infant, when born, shows little manifestation of mentality; but as its body grows, its mind develops, becoming more and more complex as the individual grows to maturity.

=The World as Dynamic.= The view of the world outlined above, and held by all scientific men of the present time, may be termed the _dynamic_ view. Man formerly looked upon the world as static, a world where everything was fixed and final. Each thing existed in itself and for itself, and in large measure independent of all other things. We now look upon things and events as related and dependent. Each thing is dependent upon others, related to others.

Man not only _lives in_ such a world, but is _part of_ such a world. In this world of constant and ceaseless change, man is most sensitive and responsive. Everything may affect him. To all of the constant changes about him he must adjust himself. He has been produced by this world, and to live in it he must meet its every condition and change. We must, then, look upon human nature as something coming out of the past and as being influenced every moment by the things and forces of the present.

Man is not an independent being, unaffected by everything that happens; on the contrary, he is affected by all influences that act upon him.

Among these influences may be mentioned weather, climate, food, and social forces.

The condition of the various organs of a child's body determine, to some extent, the effect which these various forces have upon it. If a child's eyes are in any way defective, making vision poor, this tremendously influences his life. Not only is such a child unable to see the world as it really is, but the eyestrain resulting from poor vision has serious effects on the child, producing all sorts of disorders. If a child cannot hear well or is entirely deaf, many serious consequences follow.

In fact, every condition or characteristic of a child that is in any way abnormal may lead on to other conditions and characteristics, often of a serious nature. The growth of adenoids, for example, may lead to a serious impairment of the mind. Poor vision may affect the whole life and character of the individual. The influence of a parent, teacher, or friend may determine the interest of a child and affect his whole life.

The correct view of child life is that the child is affected, in greater or less degree, by every influence which acts upon him.

=Significance of Development and Causality.= What are the consequences of the view just set forth? What is the significance of the facts that have been enumerated? It is of great consequence to our thinking when we come to recognize fully the idea of causality. We then fully accept the fact that man's body and mind are part of a causal and orderly world.

Let us consider, for example, the movement of a muscle. Every such movement must be caused. The physiologist has discovered what this cause is. Ordinarily and normally, a muscle contracts only when stimulated by a nerve current. Tiny nerve fibrils penetrate every muscle, ending in the muscle fibers. The nerve-impulse pa.s.sing into the fibers of the muscles causes them to contract. The nerve stimulus itself has a cause; it ordinarily arises directly or indirectly from the stimulation of a sense organ. And the sense organs are stimulated by outside influences, as was explained previously.

Not only are our movements caused, but our sensations, our ideas, and our feelings follow upon or are dependent upon some definite bodily state or condition. The moment that we recognize this we see that our sensations, ideas, and feelings are subject to control. It is only because our minds are in a world of causality, and subject to its laws, that education is possible. We can bring causes to bear upon a child and change the child. It is possible to build up ideas, ideals, and habits.

And ideas, ideals, and habits const.i.tute the man. Training is possible only because a child is a being that can be influenced. What any child will be when grown depends upon what kind of child it was at the beginning and upon the influences that affect it during its early life while it is growing into maturity. We need have no doubt about the outcome of any particular child if we know, with some degree of completeness, the two sets of factors that determine his life--his inheritance and the forces that affect this inheritance. We can predict the future of a child to the extent that we know and understand the forces that will be effective in his life.

The notion of causality puts new meaning into our view of the _training_ of a child. The doctrine of development puts new meaning into our notion of the _nature_ of a child. We can understand man only when we view him genetically, that is, in the light of his origin. We can understand a child only in the light of what his ancestors have been.

As these lines are being written, the greatest, the bloodiest war of history is in progress. Men are killing men by thousands and hundreds of thousands. How can we explain such actions? Observation of children shows that they are selfish, envious, and quarrelsome. They will fight and steal until they are taught not to do such things. How can we understand this? There is no way of understanding such actions until we come to see that the children and men of to-day are such as they are because of their ancestors. It has been only a few generations, relatively speaking, since our ancestors were naked savages, killing their enemies and eating their enemies' bodies. The civilized life of our ancestors covers a period of only a few hundred years. The pre-civilized life of our ancestors goes back probably thousands and thousands of years. In the relatively short period of civilization, our real, original nature has been little changed, perhaps none at all. The modern man is, at heart, the same old man of the woods.

The improvements of civilization form what is called a social heritage, which must be impressed upon the original nature of each individual in order to have any effect. Every child has to learn to speak, to write, to dress, to eat with knife and fork; he must learn the various social customs, and to act morally as older people dictate. The child is by nature bad, in the sense that the nature which he inherits from the past fits him better for the original kind of life which man used to live than it does for the kind of life which we are trying to live now. This view makes us see that training a child is, in a very true sense, _making him over again_. The child must be trained to subdue and control his original impulses. Habits and ideals that will be suitable for life in civilized society _must be built up_. The doctrine of the Bible in regard to the original nature of man being sinful, and the necessity of regeneration, is fundamentally correct. But this regeneration is not so much a sudden process as it is the result of long and patient building-up of habits and ideals.

One should not despair of this view of child-life. Neither should one use it as an excuse for being bad, or for neglecting the training of children. On the contrary, taking the genetic view of childhood should give us certain advantages. It makes us see more clearly the _necessity_ of training. Every child must be trained, or he will remain very much a savage. In the absence of training, all children are much alike, and all alike bad from our present point of view. The chief differences in children in politeness and manners generally, in morals, in industry, etc., are due, in the main, to differences in training. It is a great help merely to know how difficult the task of training is, and that training there must be if we are to have a civilized child. We must take thought and plan for the education and training of our children. The task of education is in part one of changing human nature. This is no light task. It is one that requires, in the case of each child, some twenty years of hard, patient, persistent work.

=Individual Development.= Heredity is a corollary of evolution. Individual development is intimately related to racial development. Indeed, racial development would be impossible without heredity in the individual. The individual must carry on and transmit what the race hands down to him.

This will be evident when we explain what heredity means.

By heredity we mean the likeness between parent and offspring. This likeness is a matter of form and structure as well as likeness of action or response. Animals and plants are like the parents in form and structure, and to a certain extent their responses are alike when the individuals are placed in the same situation. A robin is like the parent robins in size, shape, and color. It also hops like the parent birds, sings as they do, feeds as they do, builds a similar nest, etc. But the likeness in action is dependent upon likeness in structure. The young robin acts as does the old robin, because the nervous mechanism is the same, and therefore a similar stimulus brings about a similar response.

Most of the scientific work in heredity has been done in the study of the transmission of physical characteristics. The main facts of heredity are evident to everybody, but not many people realize how far-reaching is the principle of resemblance between parent and offspring. From horses we raise horses. From cows we raise cows. The children of human beings are human. Not only is this true, but the offspring of horses are of the same stock as the parents. Not only are the colts of the same stock as the parents, but they resemble the parents in small details.

This is also true of human beings. We expect a child to be not only of the same race as the parents, but to have family resemblances to the parents--the same color of hair, the same shape of head, the same kind of nose, the same color of eyes, and to have such resemblances as moles in the same places on the skin, etc. A very little investigation reveals likenesses between parent and offspring which we may not have expected before.

However, if we start out to hunt for facts of heredity, we shall perhaps be as much impressed by differences between parent and child as we shall by the resemblances. In the first place, every child has two parents, and it is often impossible to resemble both. One cannot, for example, be both short and tall; one cannot be both fair and dark; one cannot be both slender and heavy; one cannot have both brown eyes and blue. In some cases, the child resembles one parent and not the other. In other cases, the child looks somewhat like both parents but not exactly like either. If one parent is white and the other black, the child is neither as white as the one parent nor as black as the other.

The parents of a child are themselves different, but there are four grandparents, and each of them different from the others. There are eight great grandparents, and all of them different. If we go back only seven generations, covering a period of perhaps only a hundred and fifty years, we have one hundred and twenty-eight ancestors. If we go back ten generations, we have over a thousand ancestors in our line of descent.

Each of these people was, in some measure, different from the others.

Our inheritance comes from all of them and from each of them.

How do all of these diverse characteristics work out in the child? In the first place, it seems evident that we do not inherit our bodies as wholes, but in parts or units. We may think of the human race as a whole being made up of a great number of unit characters. No one person possesses all of them. Every person is lacking in some of them. His neighbor may be lacking in quite different ones. Now one parent transmits to the child a certain combination of unit characters; the other parent, a different combination. These characteristics may not all appear in the child, but all are transmitted through it to the next generation, and they are transmitted purely. By being transmitted purely, we mean that the characteristic does not seem to lose its ident.i.ty and disappear in fusions or mixtures. The essential point in this doctrine of heredity is known as Mendelism; it is the principle of inheritance through the pure transmission of unit characters.

An ill.u.s.tration will probably make the Mendelian principle clear. Let us select our ill.u.s.tration from the plant world. It is found that if white and yellow corn are crossed, all the corn the first year, resulting from this crossing, will be yellow. Now, if this hybrid yellow corn is planted the second year, and freely cross-fertilized, it turns out that one fourth of it will be white and three fourths yellow. But this yellow consists of three parts: one part being pure yellow which will breed true, producing nothing but yellow; the other two parts transmit white and yellow in equal ratio. That is to say, these two parts are hybrids, the result of crossing white with yellow. It is not meant that one can actually distinguish these two kinds of yellow, the pure yellow and the hybrid yellow, but the results from planting it show that one third of the yellow is pure and that the other two thirds transmit white and yellow in equal ratio.

The main point to notice in all this is that when two individuals having diverse characteristics are crossed, the characteristics do not fuse and disappear ultimately, but that the two characteristics are transmitted in equal ratio, and each will appear in succeeding generations, and will appear pure, just as if it had not been crossed with something different. The first offspring resulting from the cross--known as hybrids--may show either one or the other of the diverse characteristics, or, when such a thing is possible, even a blending of the two characteristics. But whatever the actual appearance of the first generation of offspring resulting from crossing parents having diverse characteristics, their germ-cells transmit the diverse characteristics in equal proportion, as explained above.

When one of the diverse characteristics appears in the first generation of offspring and the other does not appear, or is not apparent, the one that appears is said to be _dominant_, while the one not appearing is said to be _recessive_. In our example of the yellow and white corn, yellow is dominant and white recessive. And it must be remembered that the white corn that appears in the second generation will breed true just as if it had never been crossed with the yellow corn. One third of the yellow of the second generation would also breed true if it could be separated from the other two thirds.

It is not here claimed that Mendelism is a universal principle, that all characteristics are transmitted in this way. However, the results of the numerous experiments in heredity lead one to expect this to be the case.

Most of the experiments have been with lower animals and with plants, but recent experiments and statistical studies show that Mendelism is an important factor in human heredity, in such characteristics as color of hair and eyes and skin, partial color blindness, defects of eye, ear, and other important organs.

The studies that have been made of human heredity have been, for the most part, studies of the transmission of physical characteristics. Very little has been done that bears directly upon the transmission of mental characteristics. But our knowledge of the dependence of mind upon body should prepare us to infer mental heredity from physical heredity. Such studies as throw light on the question bear us out in making such an inference.

The studies that have been more directly concerned with mental heredity are those dealing with the resemblances of twins, studies of heredity in royalty, studies of the inheritance of genius, and studies of the transmission of mental defects and defects of sense organs. The results of all these studies indicate the inheritance of mental characteristics in the same way that physical characteristics are transmitted. Not only are human mental characteristics transmitted from parent to offspring, but they seem to be transmitted in Mendelian fashion.

Feeble-mindedness, for example, seems to be a Mendelian character and recessive. From the studies that have been made, it seems that two congenitally feeble-minded parents will have only feeble-minded children. Feeble-mindedness acts in heredity as does the white corn in the example given above. If one parent only is feeble-minded, the other being normal, all of the children will be normal, just as all of the corn, in the first generation after the crossing, was yellow. But these children whose parents are the one normal and the other feeble-minded, while themselves normal, transmit feeble-mindedness in equal ratio with normality. It works out as follows: If a feeble-minded person marry a person of sound mind and sound stock, the children will all be of sound, normal mind. If these children take as husbands and wives men and women who had for parents one normal and one feeble-minded person, their children will be one fourth feeble-minded and three fourths of them normal.

To summarize the various conditions: If a feeble-minded person marry a feeble-minded person, all the children will be feeble-minded. If a feeble-minded person marry a sound, normal person (pure stock), all the children will be normal. If the children, in the last case, marry others like themselves as to origin, one fourth of their offspring will be feeble-minded. If such hybrid children marry feeble-minded persons, one half of the offspring will be feeble-minded. It is rash to prophesy, but future studies of heredity may show that Mendelism, or some modification of the principle, always holds true of mind as well as of body.

Little can be said about the transmission of particular definite mental traits, such as the various aspects of memory, a.s.sociation, attention, temperament, etc. Before we can speak with any certainty here, we must make very careful experimental studies of these mental traits in parents and offspring. No such work has been done. All we have at the present time is the result of general observation.

=Improvement of the Race.= Eugenics is the science of improvement of the human race by breeding. While we can train children and thereby make them much better than they would be without such training, this training does not improve the stock. The improvement of the stock can be accomplished only through breeding from the best and preventing the poor stock from leaving offspring. This is a well-known principle in the breeding of domestic animals.

It is doubtless just as true in the case of human beings. The hygienic and scientific rearing of children is good for the children and makes their lives better, but probably does not affect their offspring. We should not forget that all the social and educational influences die with the generation that receives them. They must be impressed by training on the next generation or that generation will receive no influence from them. The characters which we acquire in our lifetime seem not to be transmitted to our children, except through what is known as social heredity, which is merely the taking on of characteristics through imitation. Our children must go through all the labor of learning to read, write, spell, add, multiply, subtract, and divide, which we went through. Moral traits, manners and customs, and other habits and ideals of social importance must be acquired by each successive generation.

=Heredity _versus_ Environment.= The question is often asked whether heredity or the influence of environment has the most to do with the final outcome of one's life. It is a rather useless question to ask, for what a human being or anything else in the world does depends upon what it is itself and what the things and forces are that act upon it.

Heredity sets a limitation for us, fixes the possibilities. The circ.u.mstances of life determine what we will do with our inherited abilities and characteristics. Hereditary influences incline us to be tall or short, fat or lean, light or dark. The characteristics of our memory, a.s.sociation, imagination, our learning capacity, etc., are determined by heredity. Of course, how far these various aspects develop is to some extent dependent upon the favorable or unfavorable influences of the environment. What is possible for us to do is settled by heredity; what we may actually do, what we may have the opportunity to do, is largely a matter of the circ.u.mstances of life.

In certain parts of New England, the number of men who become famous in art, science, or literature is very great compared to the number in some other parts of our country. As far as we have any evidence, the native stocks are the same in the two cases, but in New England the influences turn men into the direction of science, art, and literature. Everything there is favorable. In other parts of the country, the influences turn men into other spheres of activity. They become large landowners, men of business and affairs.

The question may be asked whether genius makes its way to the front in spite of unfavorable circ.u.mstances. Sometimes it doubtless does. But pugnacity and perseverance are not necessarily connected with intellectual genius. Genius may be as likely to be timid as belligerent.

Therefore unfavorable circ.u.mstances may crush many a genius.

The public schools ought to be on the watch for genius in any and all kinds of work. When a genius is found, proper training ought to be provided to develop this genius for the good of society as well as for the good of the individual himself. A few children show ability in drawing and painting, others in music, others in mechanical invention, some in literary construction. When it is found that this ability is undoubtedly a native gift and not a pa.s.sing whim, special opportunity should be provided for its development and training. It will be better for the general welfare, as well as for individual happiness, if each does in life that for which he is by nature best fitted. For most of us, however, there is not much difference in our abilities. We can do one thing as well as we can many other things. But in a few there are undoubted special native gifts.

SUMMARY. This is an orderly world, in which everything has a cause.

All events are connected in a chain of causes and effects. Human beings live in this world of natural law and are subject to it.

Human life is completely within this world of law and order and is a part of it. Education is possible only because we can change human beings by having influences act upon them.

Individuals receive their original traits from their ancestors, probably as parts or units. Mendelism is the doctrine of the pure transmission of unit characters. Eugenics is the science of improving the human race by selective breeding. An individual's life is the result of the interaction of his hereditary characteristics and his environment.

CLa.s.s EXERCISES

1. Try to find rock containing the remains of animals. You can get information on such matters from a textbook on geology.

2. Read in a geology about the different geological epochs in the history of the earth.

3. Make a comparison of the length of infancy in the lower animals and in man. What is the significance of what you find? What advantage does it give man?

4. What is natural selection? How does it lead to change in animals?

Does natural selection still operate among human beings? (See a modern textbook on zoology.)

5. By observation and from consulting a zoology, learn about the different cla.s.ses of animal forms, from low forms to high forms.