History of the Intellectual Development of Europe, Volume II (of 2) / Revised Edition

by John William Draper

Three distinct parts of the nervous system of man. In the nervous system of man our attention is therefore especially demanded by three essentially distinct parts—the spinal cord, the sensory ganglia, and the cerebrum. They are the automatic, the instinctive, the intellectual. Of the first, the spinal cord, the action is automatic; by its aid we can walk, from place to place, without bestowing a thought on our movements; by it we swallow involuntarily; by it we respire unconsciously. The second portion, the sensory ganglia, is, as we have seen, the counterpart of the cephalic ganglia of invertebrates; it is the place of reception of sensuous impressions and the seat of consciousness. To these ganglia instinct is to be referred. Their function is not at all impaired by the cerebrum superposed upon them. The third portion, the cerebrum, is anatomically distinct. It is the seat of ideas. It does not directly give rise to motions, being obliged to employ for that purpose its intermediate automatic associated apparatus. Dominating control of the latter. In this realm of ideas thoughts spring forth suggestively from one another in a perpetual train or flux, and yet the highest branch of the nervous mechanism still retains traces of the modes of operation of the parts from which it was developed. Its action is still often reflex. Reason is not always able to control our emotions, as when we laugh or weep in spite of ourselves, under the impression of some external incident. Nay, more; the inciting cause may be, as we very well know, nothing material—nothing but a recollection, an idea—and yet it is enough. But these phenomena are perhaps restricted to the first or anterior lobes of the brain, and, accordingly, we remark them most distinctly in children and in animals. As the second and third lobes begin to exercise their power, such effects are brought under control.

Progressive nervous development in the animal series.There is, therefore, a regular progression, a definite improvement in the nervous system of the animal series, the plan never varying, but being persistently carried [354] out, and thus offering a powerful argument for relationship among all those successively improving forms, an observation which becomes of the utmost interest to us in its application to the vertebrates. In the amphioxus, as has been said, the cranio-spinal axis alone exists; the Cyclostome fishes are but a step higher. In fishes the true cerebrum appears at first in an insignificant manner, a condition repeated in the early embryonic state both of birds and mammals. An improvement is made in reptiles, whose cerebral hemispheres are larger than their optic lobes. As we advance to birds, a further increase occurs; the hemispheres are now of nearly sufficient dimensions to cover over those ganglia. In the lower mammals there is another step, yet not a very great one. But from the anterior lobes, which thus far have constituted the entire brain, there are next to be developed the middle lobes. In the Rodents the progress is still continued, and in the Ruminants and Pachyderms the convolutions have become well marked. It attains its maximum in man. In the higher carnivora and quadrumana the posterior or tertiary lobes appear. The passage from the anthropoid apes to man brings us to the utmost development thus far attained by the nervous system. The cerebrum has reached its maximum organization by a continued and unbroken process of development.

The same progressive development occurs in each individual man.This orderly development of the nervous system in the animal series is recognized again in the gradual development of the individual man. The primitive trace, as it faintly appears in the germinal membrane, marks out the place presently to be occupied by the cranio-spinal axis, and, that point of development gained, man answers to the amphioxus. Not until the twelfth week of embryonic life does he reach the state permanently presented by birds; at this time the anterior lobes are only perceptible. In four or six weeks more the middle lobes are evolved posteriorly on the anterior, and, finally, in a similar manner, the tertiary or posterior ones are formed. And thus it appears that, compared with the nervous system of other animals, that of man proceeds through the same predetermined [355] succession of forms. Theirs suffers an arrest, in some instances at a lower, in some at a higher point, but his passes onward to completion.

It occurs again in the entire life of the globe.But that is not all. The biography of the earth, the life of the entire globe, corresponds to this progress of the individual, to this orderly relation of the animal series. Commencing with the oldest rocks that furnish animal remains, and advancing to the most recent, we recognize a continual improvement in construction, indicated by the degree of advancement of the nervous system. The earliest fishes did not proceed beyond that condition of the spinal column which is to be considered as embryonic. The Silurian and Devonian rocks do not present it in an ossified state. Fishes, up to the Carboniferous epoch, had a heterocercal tail, just as the embryos of osseous fishes of the present time have up to a certain period of their life. There was, therefore, an arrest in the old extinct forms, and an advance to a higher point in the more modern. The buckler-headed fishes of the Devonian rocks had their respiratory organs and much of their digestive apparatus in the head, and showed an approximation to the tadpoles or embryos of the frog. The crocodiles of the oolite had biconcave vertebræ, like the embryos of the recent ones which have gained the capability of making an advance to a higher point. In the geological order, reptiles make their appearance next after fishes, and this is what we should expect on the principle of an ascending nervous development. Not until long after come birds, later in date and higher in nervous advancement, capable not only of instinct, but also of intelligence. Of mammals, the first that appear are what we should have expected—the marsupials; but among the tertiary rocks, very many other forms are presented, the earlier ones, whether herbivorous or carnivorous, having a closer correspondence to the archetype than the existing ones, save in their embryonic states, the analogies occurring in such minor details as the possession of forty-four teeth. Absolute necessity of admitting transmutation of forms. The biography of the earth is thus, on the great scale, typical of individual life, even that of man, and the succession of species in the [356] progress of numberless ages is the counterpart of the transmutation of an individual from form to form. As in a dissolving view, new objects emerge from old ones, and new forms spontaneously appear without the exercise of any periodical creative act.

Life of man from infancy to maturity in accordance with his anatomy.For some days after birth the actions of the human being are merely reflex. Its cranio-spinal axis alone is in operation, and thus far it is only an automaton. But soon the impressions of external objects begin to be registered or preserved in the sensory ganglia, and the evidences of memory appear. The first token of this is perhaps the display of an attachment to persons, not through any intelligent recognition of relationship, but merely because of familiarity. This is followed by the manifestation of a liking to accustomed places and a dread of strange ones. At this stage the infant is leading an instinctive life, and has made no greater advance than many of the lower mammals; but they linger here, while he proceeds onward. He soon shows high powers of memory, the exercise of reason in the determinations of judgment, and in the adaptation of varied means to varied ends.

Such is therefore the process of development of the nervous system of man; such are the powers which consequently he successively displays. His reason at last is paramount. No longer are his actions exclusively prompted by sensations; they are determined much more by ideas that have resulted from his former experiences. While animals which approach him most closely in construction require an external stimulus to commence a train of thought, he can direct his mental operations, and in this respect is parted from them by a vast interval. The states through which he has passed are the automatic, the instinctive, the intellectual; each has its own apparatus, and all at last work harmoniously together.

Every person consists of two lateral individuals.But besides this superposition of an instinctive apparatus upon an automatic one, and an intellectual upon an instinctive, the nervous system consists of two equal and symmetrical lateral portions, a right half and a left. Each person may be considered as consisting in reality of two individuals. [357] The right half may be stricken with palsy, the left be unimpaired; one may lose its sight or hearing, the other may retain them. These lateral halves lead independent lives. Yet, though independent in this sense, they are closely connected in another. The brain of the right side rules over the left half of the body, that of the left side rules over the right of the body. Consequences of this doubleness of construction. On the relationships and antagonisms of the two halves of the cerebro-spinal system must be founded our explanations of the otherwise mysterious phenomena of double and alternate life; of the sentiment of pre-existence; of trains of thought, often double, but never triple; of the wilful delusions of castle-building, in which one hemisphere of the brain listens to the romance suggestions of the other, though both well know that the subject they are entertaining themselves with is a mere fiction. The strength and precision of mental operations depend as much upon the complete equivalency of the two lateral halves as upon their absolute development. It is scarcely to be expected that great intellectual indications will be given by him, one of whose cerebral hemispheres is unequal to the other. But for the detailed consideration of these topics I may refer the reader to my work on Physiology. He will there find the explanation of the nature of registering ganglia; the physical theory of memory; the causes of our variable psychical powers at different times; the description of the ear as the organ of time; the eye as the organ of space; the touch as that of pressures and temperatures; the smell and taste as those for the chemical determination of gases and liquids.

Conclusions from the foregoing anatomical facts. From a consideration of the construction, development, and action of the nervous system of man, we may gain correct views of his relations to other organic beings, and obtain true psychical and metaphysical theories. There is not that homogeneousness in his intellectual structure which writers on those topics so long supposed. It is a triple mechanism. Man a member of the animal series. A gentle, a gradual, a definite development reaches its maximum in him without a breach of continuity. Parts which, because of their completion, are capable of yielding in him such splendid [358] results, are seen in a rudimentary and useless condition in organisms very far down below. On the clear recognition of this rudimentary, this useless state, very much depends. It indicates the master-fact of psychology—the fact that Averroes overlooked—that, while man agrees with inferior beings in the type of his construction, and passes in his development through transformations analogous to theirs, he differs from them all in this, that he alone possesses an accountable, an immortal soul. It is true that there are some which closely approach him in structure, but the existence of structure by no means implies the exercise of functions. In the still-born infant, the mechanism for respiration, the lungs, is completed; but the air may never enter, and the intention for which they were formed never be carried out.

His life and that of the planet alike.Moreover, it appears that the order of development in the life of individual man and the order of development in the life of the earth are the same, their common features indicating a common plan. The one is the movement of a few hours, the other of myriads of ages. This sameness of manner in their progression points out their dependence on a law immutable and universal. The successive appearance of the animal series in the endless course of time has not, therefore, been accidental, but as predetermined and as certain as the successive forms of the individual. In the latter we do not find any cause of surprise in the assumption of states ever increasing in improvement, ever rising higher and higher toward the perfection destined to be attained. We look upon it as the course of nature. Why, then, should we consider the extinctions and creations of the former as offering any thing unaccountable, as connected with a sudden creative fiat or with an arbitrary sentence of destruction?

Progress of humanity is according to law.In this book I have endeavoured to investigate the progress of humanity, and found that it shows all the phases of individual movement, the evidence employed being historical, and, therefore, of a nature altogether different from that on which our conclusions in the collateral instances rest. It may serve to assure us that the ideas here presented [359] are true when we encounter, at the close of our investigation, this harmony between the life of the individual, the life of society, and the life of the earth.