Pedagogical Anthropology, Maria Montessori [online e book reader TXT] 📗

Fig. 82.—Growth of Cranial Circumference.

In all the widely varied series of pathological and degenerate individuals who are included under the generic names of "deficients" and "criminals," there is a notable percentage of crania that are abnormal both in volume and in form; the percentage of crania with normal dimensions is less than that of the crania which exceed or fall below such dimensions, and among these there is a preponderance of submicrocephalic crania: a morphological characteristic associated with a partial arrest of cerebral development, due to internal causes and manifested from the earliest period of infant life.

The accompanying chart (Fig. 82) demonstrates precisely this fact. It represents the growth of the cranium in normal and in abnormal children. The abnormal are at one time superior and at another inferior to the normal children; but their general average shows a definite inferiority to the normal. Lombroso established the fact that among adult criminals there is an inferiority of cranial development, frequently accompanied by a stature that is normal, or even in excess of normality.

Quite recently, Binet has called attention to a form of submicrocephaly acquired through external causes, which is of great interest from the pedagogic point of view. Blind children and those who are deaf-mutes have, up to the seventh or eighth year, a cranium of normal dimensions, but by the fourteenth or fifteenth year the volume is notably below the normal, and this stigma of inferiority remains permanently in the adults. This fact, which is of very general occurrence, is attributed by Binet to a deficiency of sensations, and consequently a deficiency of certain specific cerebral exercises.

This whole question has a fundamental interest for us as educators, because it affords an indirect proof that cerebral exercise develops the brain, or in other words, that education has a physical and morphological influence as well as a psychic one.

This question, coupled with that of the influence of alimentation upon the development of the head, leads to the conclusion that a two-fold nutriment is necessary for the normal development of man: material nutriment and nutriment of the spirit.

It follows that education must be considered from two different points of view: that of the progress of civilisation, and that of the perfectionment of the species.

In regard to variations of cranial volume, just as in the case of variations of stature, there are a number of different factors which may be summed up in such a way as to afford us certain determining characteristics of social caste. Delicate questions these, which we may sum up in a single question equally delicate, that lends itself to a vast amount of discussion; namely, what is the relation between the volume of the brain and the development of the intellect?

Individual Variations of Cerebral (and Cranial) Volume. Relation between the Development of the Cerebral Volume and the Development of the Intelligence.—The series of arguments in reference to the cerebral volume ought to be considered independently of the biological and biopathological factors which we have up to this point been considering; namely, race, sex, age, degeneration and disease.

That is to say, in normal individuals, other conditions being equal, volumetric differences of the brain may be met with, analogous to those other infinite individual variations, in which nature expresses her creative power, even while preserving unchanged the general morphology of the species.

It is due to this fact that the innumerable individuals of a race, while all bearing a certain resemblance to one another, are never any two of them identically alike.

Variations of this sort, which might be called biological individualisations, are in any case subject to the most diverse influences of environment, which concur in producing individual varieties.

This is in accordance with general laws which are applicable to any biological question whatever, but that in our case assume a special interest. There are certain men who have larger or smaller brains; and there are men of greater or of less intelligence. Is there a quantitative relation between these two manifestations, the morphological and the psychic?

Everyone knows that this is one of those complicated, much discussed questions that spread outside of the purely scientific circles and become one of the stock themes of debate among classes incompetent to judge; consequently it has been colored by popular prejudice, rather than by the light of science. It is well that persons of education should acquire accurate ideas upon the subject.

If the volume of the brain should be in proportion to the intellectual development, argues the general public, what sort of a head must Dante Alighieri have had? He would have had to be the most monstrous macrocephalic ever seen upon earth. And on the basis of this superficial observation, they wish to deny any quantitative relation whatever between brain and intelligence. And yet it is this same general public that keeps insisting: Woman has less intelligence than man, because she has a smaller brain.

A single glance up and down the zoological scale suffices to show that throughout the whole animal series a greater development of brain is accompanied by a correspondingly greater development of psychic activity; and that there is a conspicuous difference between the human brain and that of the higher animals (anthropoid apes), corresponding to the difference between the level of man's psychic development and that of the higher mammals; and this justifies the assertion that, as a general rule, there is a quantitative relation between the brain and the intellect.

This suggests the thought that the perfect development of this delicate instrument, the brain, demands a variety of harmonious material conditions, among others the volume, in order to render possible the conditions of psychic perfection.

From this premise, we may pass on to a more particularised study of the material conditions essential to the superior type of brain. The volume is the quantitative index; but the quality may be considered from various points of view, which may be grouped as follows:

I. The General Morphology of the Brain in reference to:

(a) The harmonious, relative volumetric proportions between the lobes of the brain (namely, the proportion between the frontal, parietal, temporal and occipital lobes). It was formerly believed that a superior brain ought to show a prevalence of the frontal lobes, since a lofty forehead is a sign of intellect; but it was afterward established that there is no direct relation between the development of the forehead and the development of the frontal lobes; a higher forehead results from a greater volume of the entire cranial contents; the superior brain, on the contrary, is that in which no one lobe prevails over another, but all of them preserve a reciprocal and perfect harmony of dimensions.

(b) The form, number and disposition of the cerebral convolutions, and of the folds of the internal passage (Sergio Sergi).

(c) The form, number and disposition of the cells in the cortical strata of the brain, and the proportion between the gray matter and the white, that is to say, between the cells and fibres; in short, the histological structure of the brain.

II. The Chemistry of the brain:

(a) The chemical composition of the substances constituting the brain, which may be more or less complicated. (Recent studies of the chemical evolution of living organisms have demonstrated that the atomic composition is far more complex in the higher organisms.)

(b) The intimate interchange of matter in the cerebral tissues, in connection with their nutrition.

(c) The chemical stimuli coming from the so-called glands of internal secretion (thyroid, etc.).

All these conditions concur in determining the quality of the cerebral tissues. In its ontogenetic evolution, for example, the brain does not merely increase in volume, and its development is not limited to attaining a definite morphology; but its intimate structure and its chemical composition as well must pass through various stages of transition before attaining their final state. We know, for example, that the myelination of the nerve fibres takes place upward from the spinal marrow toward the brain, and that the pyramidal tracts (voluntary motor tracts) are the last to myelinate, and hence the last to perform their functions in the child.

The consistence of the cerebral mass and its specific gravity also differ in childhood from that of the adult state. The evolution of the brain is therefore a very complex process; and this process may not be fully completed (for instance, it may be completed in volume, but not in form or chemical composition, etc.).

Consequently, just as in the case of volume, there may be various qualitative conditions, such as would produce organic inferiority.

But supposing that qualitatively the evolution has been accomplished normally, where there is greater cerebral volume, is there a correspondingly greater intellect?

At this point it is necessary to take into consideration another series of questions regarding the brain considered as a material organ, and having reference to the relation between the volume of the brain and that of the stature.

The brain must govern the nerves in all the active parts of the body, especially the striped muscles, which perform all voluntary movement. Consequently the cerebral volume must be in proportion, not only to the intellectuality, but also to the physical activity.

Evidently, a greater mass of body demands a greater nervous system to give it motive power.

The biological law is of a general nature: if the brain of a rat weighs 40 centigrams, that of an ox weighs 734 grams, and that of an elephant 4,896 grams.

"The absolute volume of the brain increases with the total volume of the body."

But this correspondence is not proportional. There are two facts that alter the proportions. One of these is that the mass of the body increases faster than the brain, throughout the biological series of species, so that the smaller the body the greater the proportional quantity of brain. Just the opposite from what was found to hold true for the absolute weight.

It may be affirmed as a biological law that "the relative volume of the brain increases as the size of the body diminishes." For instance, the tiny brain of a rat is a 43d part of the total volume of its body; the brain of an ox, on the contrary, is a 750th part. Consequently we may say that the little rat has relatively a far larger brain than the huge ox.

And the same thing holds true among men; those of small build have a proportionately larger brain than those of large build.

A second fact which alters the absolute proportion between the volume of brain and the volume of body has reference to the "functional capacity" of the active parts. The muscles which are capable of the best activity and the greatest agility are the ones more abundantly stimulated through their nerves than those which are capable only of slow and sluggish action. The same may be said of the organs of sensation; the more highly the sensibility is developed, the larger are the corresponding nerves, and consequently the greater is the corresponding quantity of cerebral cells. Accordingly the animal which is nimblest in its movements, and most capable of sensations has in proportion to this greater functional activity a greater cerebral volume. In this same way we may explain the enormous difference in relative brain volume between the extremely active, sensitive and intelligent little beast which we call the rat, and the sluggish and stupid animal which we call the ox. Consequently this functional activity has a correspondingly greater volume of brain, without a correspondingly greater volume of the various highly sensitized organs. In such a case it may be stated as a general law that "the relative volume of the brain is in direct proportion to the intelligence (or, more broadly, to the functional activity), while the absolute volume is in direct relation to the total mass of the body."

Man has a cerebral volume of 1,500 cubic centimetres, a volume equal to a fortieth part of the whole body. Consequently he has a brain twice