Creation by Evolution/The Evolution of the Brain
THE EVOLUTION OF THE BRAIN
By G. Elliott Smith
Professor of Anatomy in the University of London
In ancient times, before paper or good parchment was easy to obtain, writers used the leaves of old manuscripts again and again after attempting to erase the writing already inscribed on them. On examining one of these palimpsests, as they are called, the modern student may be able to read sufficient of its partly erased writing to decipher the story it told. The human body is a palimpsest, which has preserved in its every part the records of its inheritance, so that anyone who carefully studies its structure and compares it with the bodies of other living creatures can read the history of man written in imperishable symbols in its very texture. Seen in this light the structure of every bone and muscle, the arrangement of the blood vessels and nerves, the constitution of the organs of body, indeed, the nature of every tissue of the organism, proclaim the fact that, wonderfully as each and every part seems to have been designed to perform its particular function, it is really a readaptation of an organ or tissue that may originally have served a useful purpose very different from that which it serves now. Like the ancient palimpsests, the human body has been inscribed again and again with new devices that have only partly obscured the more ancient writings. Let us take two illustrations:
1. At a certain stage in the normal development of a human infant a real tail, complete, with all the muscles for wagging it, is formed; but after two or three weeks it begins to dwindle, and it finally disappears. Some of its muscles also atrophy; others are put to new purposes. No longer having any use as tail-movers, once the tail had vanished, they became converted into muscles that help to support and control certain organs of the body. Similar transformations can be found in every part of the human body; an organ or tissue that was originally developed for one purpose becomes modified to serve a totally different purpose. These statements about the tail are not theories or hypotheses, they are simple statements of fact, which any one can confirm by looking at a human embryo that has reached the third month of its development or at photographs of the embryo at that stage, which can be studied in any text-book of anatomy or embryology. The human embryo is at this stage so nearly identical with that of the monkey, dog, and pig at corresponding stages that only those who have expert knowledge can distinguish one from another. In fact, in many medical schools students examine the embryos of pigs to acquire a practical knowledge of the development of man.
2. In some animals that live in trees there is a peculiar muscle in the fore limb, or arm, which plays a part in the acrobratic feat of swinging from branch to branch. In the human arm this muscle is commonly missing, but it is sometimes found as a small and apparently useless vestige, a band of fibrous tissue representing a muscle that was a part of the bodies of our arboreal ancestors.
Neither of these illustrations is unique. The structure of any and every part of the human body tells the same sort of story of its history and affords the most unquestionable proof of the reality of man’s ancient lineage and of the immense antiquity of his pedigree. The student who is searching for the truth and is competent to appreciate the significance of the facts revealed in the great adventure of exploring the structure of the human body cannot fail to discover that he himself is carrying about with him, inscribed in the very texture of his body, the record of his ancestry and of an inheritance that links him to all other living creatures.
It is often contended that such an interpretation of the evidence is merely a theory, or even nothing better than a mere working hypothesis. I want to assure my readers that such statements are very misleading—that they are actually evasions of the truth. Man’s kinship with other living creatures is established by evidence afforded by his own structure, by the mode of development of his body, by the mode of action of his every tissue. We can clearly see, in the most concrete application of the term, a blood relationship.
For special consideration I have selected one particular organ of the body, the brain, because it raises the problem, of the evolution, not merely of man’s physical body, but of his mind, which, after all, is his most distinctive attribute. By virtue of his mental endowment man enjoys a wide vision of the world in which he lives and a high appreciation of its beauties. This endowment confers upon him powers of insight and foresight that are denied to all other living creatures. By means of speech, which the human brain makes possible, he is able to share his knowledge with his fellows, to learn from them, and to hand on the results of his accumulated experience from one generation to another.
Remembering what the human mind has achieved, the wide range of thought it has attained, the feeling for truth and beauty it has cultivated, the wonderful institutions it has created, the flights of constructive imagination it has expressed in literature and science in interpreting the meaning of human experience and the natural laws of the universe, and the thousand and one ways by which it has put into the hands of mankind the means of adaptation to the changing conditions of existence, we would seem to have some excuse for regarding men, endowed with such unique powers of intellect and sentiment, as beings fundamentally different from all other living creatures. Hence it is not surprising that the suggestion has found expression, even among such confirmed believers in evolution as, for example, Darwin’s famous collaborator Wallace, that the mind is a distinctively human attribute, something that is lacking in other animals, the possession of which by man puts him in a class by himself. But no one who has made a companion of a dog and appreciates the reality and depth of his feelings and emotions, the knowledge he acquires by experience, and the sympathy and intelligence he displays in his behavior, can deny that the dog also has a mind. Though his aptitude to learn and to understand is infinitely less than that of a human child, though he seems unable clearly to anticipate what is going to happen and lacks the means of sharing knowledge that speech confers upon mankind, no one can deny that the dog is endowed with intelligence, which differs from man's intelligence not so much in its essential qualities as in its degrees—in the range of the understanding which it confers.
However, I shall not here try to define what the mind is or to discuss the question of the reality of animal intelligence. My aim is rather to call attention to the knowledge we have acquired of the instruments through which the mind expresses itself and manifests its wonderful versatility.
Every part of the human body is in a sense an instrument of the mind, a mechanism whereby its purpose can find expression—the legs that carry us, the hands that perform an infinite variety of delicately adjusted actions in the service of the will, the eyes that see, the ears that hear, the hands that feel—these and scores of other complicated pieces of mechanism in the body are surely the mind’s instruments, such as in many other living creatures perform essentially the same functions that they serve in man. But almost every organ in the body plays a part in determining the appetites and desires, the feelings and the thoughts. In ancient times the Bible gave expression to the views then current among men and attributed such influences to “the reins and the heart” and to the bowels that were said “to yearn.” Modern science has revealed with greater precision the part each organ plays (by means of its nervous connections as well as by the “chemical messengers” or hormones it discharges into the blood stream) in stimulating the dominant appetites and affecting our feelings and emotions—in fact, in shaping our behaviour.
I have mentioned these conceptions merely to emphasize the fact that no one organ or part of the body can be regarded exclusively as the organ of the mind, seeing that each and all, in their several fashions, may serve as instruments in exciting or expressing human behaviour. But I want to direct particular attention to the organ that plays the dominant part in our mental life—the organ whereby we are made aware of the sensory experiences that we call sight, hearing, smell, taste, and touch and all the other varieties of sensation, as well as of the feelings, appetites, and sentiments. This organ, however, controls the complicated reactions that find expression in behaviour. I do not intend to discuss the nature of the relationship between the activities of the brain and the phenomena of mind; my purpose is to call attention only to certain well-recognised facts and to discuss their meaning. We know that damage inflicted by disease or injury upon certain parts of the brain affects the mind in different ways, ranging widely from purely sensory and motor changes, such as blindness or the loss of the voluntary control of certain movements, to the most profound interference with understanding and personality. If, then, the manifestations of intelligence are in some way linked to certain bodily structures, some at least of which can be identified and examined, it becomes a matter of special interest to discover wherein the human brain differs from that of other living creatures, between whose intellectual powers and those of man there is so vast a chasm.
For more than a century anatomists have been making detailed comparisons between the brains of men and those of other creatures known as mammals, which resemble mankind in being provided with hair and with milk-producing glands for feeding their infants. It was hoped in this way to discover the secret of man's peculiar intellectual powers. Although a common and very distinctive plan of architecture is found in the brains of different mammals, an examination of their size, form, and structural details reveals a wide range of variation. The question arises whether it is possible to correlate these contrasts in the brain with the variant capabilities of the respective animals and to discover any outstanding distinctive features in the human brain that are at all commensurate with man's intellectual supremacy. A century ago, in order to explain what in those days were termed the distinctive “faculties” of man's mind, investigators plunged into this inquiry with the conviction that the human brain must contain certain organs of structures peculiar to itself. One anatomist after another put forward the claim that he had found in a certain structure evidence to substantiate man's intellectual preeminence, only to provoke someone else to discover the same structure in some non-human brain. Scores of such futile claims have been made decade after decade. But at last we have learned that there is no distinctive structure in the human brain; there is no tissue or formation that is not found in apparently as highly differentiated form in the brains of certain non-human animals. What then, it will be asked, is the real difference between the human organ of mind and that of the ape, which approaches man’s brain most nearly in form?
If the brains of a series of mammals are compared, differences in shape and pattern at once become obvious. The anatomist can discriminate between them as easily as he can recognize the animals themselves. For example, compare the brain of a lion with that of a gorilla (Figs. 1 and 2). In both a great body of tissue (cerebral cortex known as the neopallium) is built up above the smaller mass that formed the older type of brain, a mass that was conjoined mainly with the sense of smell and that is relatively larger and more potent in the lion than in the ape (compare Figs. 1 and 2). The neopallium is the receptive organ of such senses as vision, hearing, and touch; it is the instrument whereby the information brought into the brain by these special senses can be blended and recorded so as to be recalled in memory and to influence the movements and behaviour of the whole organism.
By comparing the brains of the lion and the gorilla, creatures of roughly the same bulk, we may see that, although in the lion the sense of smell is more strongly represented than in the gorilla, the other senses (expressed in the neopallium) are much more strongly represented in the ape (Fig. 2). Moreover, the plan formed by the folding of the neopallium in the lion (Fig. l) seems to be so utterly unlike that of the ape that anatomists are still disputing whether
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Figs. 1, 2, 3.—Brains of a lion (Fig. 1), a gorilla (Fig. 2), and a human being (Fig. 3), seen from the left side.
there is any homology. Bearing in mind these profound differences in pattern it comes as something akin to a shock to discover that the general pattern of the brain of a gorilla (Fig. 2) is essentially identical with that of the brain of a man (Fig. 3). In spite of the fact that the exceptionally small and very primitive human brain represented in Fig. 3 is double the bulk of the ape’s (1,000 grammes and 500 grammes, respectively), the form and pattern of the gorilla’s brain so closely reproduce those of the human brain that it is easy to recognise corresponding areas in the two. By comparing these areas the further fact emerges that the parts that receive the impulses of vision, hearing, and touch are almost, if not quite, as extensive in the brain of the ape as in the brain of man. In fact, the only noteworthy differences are due to the enormous expansion in the human brain of three areas, the representatives of which in the gorilla’s brain (distinguished by stars in Fig. 2) are comparatively insignificant. Studies of the effects of diseases or injury upon the brain has shown that damage to these particular areas of man’s brain has the most profound effects upon intelligence and personality. Moreover, one who studies the microscopic structure of these areas that we know to be concerned with the expression of man’s highest mental powers, the instruments of his distinctive intelligence and personality, can detect no difference in structure or quality between them and their diminutive representatives in the brain of the ape.
The accompanying diagrams show the profound contrast between the patterns of the brains of the lion and the gorilla and throw into relief the remarkable identity of structure of the brains of the gorilla and of man, although the human brain is double the volume of the gorilla’s. The human brain chosen for this purpose is exceptionally small (about two-thirds the average size) and is primitive in type. The difference in size is confined almost wholly to three areas, and it is profoundly significant that the areas which reveal the enormous expansion in the human brain are precisely those that attain their maturity latest in the human child (Fig. 4). The more precocious, such as 1 (the area concerned_p320_brain_of_human_child.png)
Fig. 4.—Brain of a child.
The physical instruments that are the sources of man’s highest mental qualities are thus represented in the brain of the ape. Their construction in both is identical, but in the ape they are very much smaller. The difference between the brain of a man and the brain of an ape are not qualitative but quantitative. The ape has the germs of the mental powers that are man’s supreme distinction. This conclusion has recently been confirmed by the careful observations of Professor Yerkes of Johns Hopkins University and Professor Köhler of Berlin, who have devoted years to the study of the chimpanzee’s behaviour. When serious consideration is given to the identity of structure in the brain of man and the brain of the man-like ape—even though the ape’s brain may be but half or a third of the bulk of the human brain—the only conception that affords a credible explanation of the resemblance is that ape and man had their origin in a common, even if very remote ancestor.
But if it be admitted that men and apes are derived from a common source, though the apes have neglected to develop their possibilities as men have done, the implication is that the work accomplished by man’s brain, which finds expression in the human mind and personality, must necessarily be of the same kind that a brain of simian type is capable of doing and that man has been evolved from some lower type.
It must not be forgotten that on the most conservative estimate it is much more than a million years since the ancestors of man and of the apes parted company from their common parents. The apes gradually lost the power to develop further the brain and the mind in the way that the ancestors of man were able to do, because the apes became adjusted to particular modes of life, so that their brains and hands, and in fact their entire bodies, lost that power of adaptation to new or changing conditions which the ancestors of man retained. Hence it is altogether unlikely that in the future any ape can be transformed into a man. The ape’s thumb is already so atrophied that it can never regain its adaptability, and without adaptable hands, which are the instruments for applying knowledge and for developing skill, the brain cannot progress in the way necessary to attain the human type of intelligence.
At one time it was generally believed, as I have already remarked, that the ape’s brain has distinctive features, which were lacking in the human brain. One of these was regarded as so eminently characteristic of monkeys and apes (Fig. 2), that it was called “the ape-fissure,” or more usually Affenspalte, the German equivalent of this expression. But all these features, and in particular the so-called “ape-fissure,” have now been found in the human brain (Fig. 3). The fact that they were formerly believed to be so peculiarly distinctive of the apes assumes special significance now that their presence has been demonstrated in the human brain; for they become further tokens of the close affinity between man and the ape—labels, so to speak, to force us to recognise in the organ that is in a sense the physical expression of man’s intellectual supremacy the evidence establishing its community of origin with the brain of the ape.
Nor must we restrict the brain’s activities to the regulation of the bodily functions and the manifestation of intelligence. The brain is the organ that controls behaviour. As Charles Darwin said, more than fifty years ago: “A moral being is one who is capable of comparing his past and future actions or motives, and of approving or disapproving of them. We have no reason to suppose that any of the lower animals have this capacity; therefore, when a Newfoundland dog drags a child out of the water or a monkey faces danger to rescue its comrade or takes charge of an orphan monkey we do not call its conduct moral.” If this be admitted it follows that one of the essential conditions for the display of moral qualities depends upon the integrity of certain parts of the brain, without which it would not be possible to recall the past or to speculate about the future. Memory and foresight do not, of course, confer moral qualities, but they do represent conditions essential for the display of such humanitarian attributes.
Only during the last century has any accurate information been acquired as to which parts of the brain are concerned with the intellectual functions. Even at the present moment the terrible effects of the damage inflicted upon the brains of patients suffering from what is popularly known as “sleeping sickness” are opening new vistas of knowledge as to the parts of the brain upon whose activities personality, the sentiments and emotions, muscular skill, and intellectual and moral capabilities depend. In scores of patients, during the last five years, physicians have witnessed the most profound changes in character and morals when this insidious disease has destroyed certain small areas of the brain.
Three centuries before the beginning of the Christian era some of the wise men of Greece already recognised in the brain the real organ of the mind; yet it was reserved for modern times to confirm the accuracy of this early knowledge and to extend it. In olden times the seat of the understanding was placed in the heart, as every reader of the Old Testament must be aware, although certain passages in the Bible suggest that sometimes the kidneys were regarded as the organs of mind, or both the kidneys and the heart, as in the New Testament (Revelation, II, 23), where the Son of God says: “I am he that searcheth the reins and the heart.”
Even the Psalmist who wrote the oft-quoted verses (Psalm CXXXIX, 13–16), which have become the special hymn of the anatomist and embryologist, begins with the suggestion that the kidneys are the seat of the will:
Thou hast possessed my reins:
Thou hast covered me in my mother’s womb.
I will praise thee: for I am fearfully and wonderfully made: marvellous are thy works,
And that my soul knoweth right well.
My substance was not hid from thee
When I was made in secret
And curiously wrought in the lowermost parts of the earth.
Thine eyes did see my substance yet being imperfect,
And in thy book all my members were written which in continuance were fashioned
When as yet there was none of them.
But of all these works none is so marvellous, so fearfully and wonderfully made as the brain, which confers upon man the supreme distinction of his high powers of intelligence.
The brain affords evidence in corroboration of man’s origin from an ancestor common to man and ape that is too exact and impressive to admit of any doubt as to its significance. By demonstrating that the structures concerned in the highest expressions of human intelligence are already present in the ape’s brain, even if they are very diminutive, the study of the brain adds strength to the conviction that the mind as well as the brain has been evolved. The fact that the Bible in various places assigns the chief seat of understanding sometimes to the heart, at other times to the kidneys, or both heart and kidneys, has not been allowed to interfere with the general recognition of the preëminence of the brain as the organ of mind. Why, then, should any difficulty be raised in opposition to the patent fact that the brain itself “in continuance was fashioned,” in strict accordance with an inherited plan, which is common also to that of our nearest living relations in the animal world?
I have here called attention to the fact that the rapid development of our knowledge of the human brain and of the effects of injury of disease to different parts of it has made it possible for us to identify the structures whose activities find expression as mind and personality. In the brains of other living creatures corresponding structures can be detected, which conform in every respect except size to those areas which in man we have recognized as the special instruments of the mind. The resemblance of the brain of some creatures, like the chimpanzee and gorilla, to the brain of man is much closer than that of either to the brain of any other animal. The only reasonable and satisfying explanation of such close resemblances, both in structure and in function, is the inference that (a) these other creatures have the undeveloped germs of a mind similar in kind to man’s (one, however, that has definitely lost the power of significant development or further progress of the kind distinctive of man’s immediate ancestors), and (b) that both the brain and the mind of man are the results of a long process of development from ancestors common to those of other living creatures having brains of the same essential type.
SELECTED REFERENCES
- Smith, G. Elliot. Essays on the Evolution of Man. Oxford University Press, 2d ed., 1927.
- Herrick, C. Judson. Introduction to Neurology. W. B. Saunders, Philadelphia and London, 1920.
- Kappers, C. V. Ariens. Cerebral Localization and the Significance of Sulci, Report of the XVIIth International Congress of Medicine, 1913, Oxford University Press.
In all three works, and especially No. 3, further bibliographical references will be found.
Lyell, in a letter to John Hershel, in 1830, wrote: “When I first came to the notion . . . of a succession of extinction of species, and the creation of new ones, going on perpetually now, and through an indefinite period in the past, and to continue for ages to come, all in accommodation to the changes which must continue in the inanimate and habitable earth, the idea struck me as the grandest which I had ever conceived, so far as regards the attributes of the Presiding Mind.”
“It is plain that neither in ‘systematic theology’ nor in science has the last word been said. In astronomy, in physics, in life, in space, in time, in thought, we find ourselves baffled in the face of Infinity. The Master Key that shall unlock all doors which open toward the center, no man has yet found. It too must lie within the gates of Infinity!”—David S. Jordan.
“Organic evolution states most emphatically that species are not fixed and unchangeable, and were not created in one sudden stroke, but that they have varied considerably and that the forms now existing have slowly developed from more primitive ancestors.”—Joseph Meyer.
“To understand what has happened, and even what will happen we have only to examine what is happening.”—Buffon.
Evolutionists, Darwin included, do not say that man is descended from any existing kind of ape or monkey, but that pro-man and ape, in the dim and distant past, had a common ancestor, now extinct, that was neither man nor ape.—Editor.