Being Well-Born: An Introduction to Eugenics

by Michael F. Guyer

Skill Acquired in One Special Branch of Learning Probably Not Transferred to Another Branch.—Such a differential arrangement of the brain-mechanism which presumably underlies the various mental abilities would lead to the inference that skill in one special branch of learning, in so far as it involves only certain centers of the cortex, would not be transferred to another branch based on different neural pathways and centers. Development of historical knowledge, for example, would not enhance one’s mathematical ability, or vice versa. The testimony of various psychologists bears out this idea. In so far as certain factors of training, such as habits of industry, concentration, etc., are common to the study of either mathematics or history, the good effects of either discipline will probably be much the same, but the identity of effect vanishes as soon as the intrinsic characteristics of the subjects themselves are involved.

Just how far we are warranted, however, in carrying this idea of localized functions as regards the association areas is a moot question. Our present attitude regarding the specificity of such localizations is largely a matter of inference based on analogy to conditions which obtain in other and better known parts of the brain, together with the indubitable differences in inborn abilities which exist between individuals. Some few brain physiologists maintain that the whole cortex operates more or less as a unit in all of the higher psychical activities.

Preponderance of Cortex in Highest Animals.—One of the most interesting conditions in the nervous system of the highest types of animals is the way in which the cortex has outrun the other parts of the brain in size and complexity and has come to dominate the organism more and more both directly and indirectly. Aside from the proportionately greater increase in size of the cortex, there is an abundance of anatomical evidence of this altered and probably altering system of control in man and the higher apes. This is well illustrated in the fiber tracts (nerve bundles) of the spinal cord.

More Long Fiber Tracts in the Spinal Cord of Man.—The spinal cord although having many nerve centers of its own is also in great part a large cable for conducting enormous numbers of fibers from one part of the cord to another, or to and from the brain. In man and the higher apes a considerably larger percentage of the total area of the cord is given up to the long fiber tracts from the brain to the body than in lower vertebrates. This progressive increase in long fiber tracts in the higher anthropoids probably marks more and more domination of the body by the higher brain centers and correspondingly less by the direct activity of the cord and by the lower brain centers. However, even in man, many of the simpler reflexes of the body still have their centers in the spinal cord.

Special Fiber Tracts in the Cord of Man and Higher Apes.—There are certain special tracts of the cord that are particularly interesting in connection with the increasing domination of the brain over the body, namely, the pyramidal tracts. These were the latest tracts to appear in the animal kingdom and are apparently the latest to become functional in the individual. It is believed that the development of the medullary substance (an enveloping sheath) of the common medullated nerve fiber marks the time of entrance of the fiber into activity and it is a significant fact that the formation of this sheath occurs last of all in the fibers of the pyramidal tracts, where it does not appear till after birth. These tracts convey impulses from the brain to the body. They consist of two sets of tracts, in fact, one the crossed, the other the direct. As an anomaly, probably arising most frequently from instrumental injury at birth, the pyramidal tracts fail to develop normally, with the distressing result that the infant, although possessing perfectly normal brain activity and normal spinal cord reflexes, is unable to exercise voluntary control of the body. In other words the condition, like hare-lip, is one of suppressed development. At least this seems to be the most plausible explanation of what is known as Little’s disease. Such unfortunates usually die early although they may survive for a few years.

The direct pyramidal tracts occur only in man and man-like apes. They vary considerably in extent in different individuals. They originate in nests of characteristic large cells located in the cerebral cortex and are regarded as paths, though not the only ones, through which volitional impulses are conveyed from the brain. They seem to control certain of the finer and more delicate movements of the body.

Great Complexity in Associations and More Neurons in the Brain of Man Than of Other Animals.—It has already been noted that as animals stand higher in the scale of life while the general plan of their neural elements remain the same, there is increasing complexity in the number and connections of the neurons. The number of processes on individual nerve-cells is also greater. There is in fact much greater complexity in the number of processes and the inter-connections of the neural cells than in the numbers of the cells themselves. This would seem to indicate that the greater mental activities of higher animals depend more on richness in complex associations than on mere increase in number of neurons. The latter, however, is by no means unimportant as may be seen in man, for instance, in whom it is estimated that the cerebral cortex, that is, that part of his brain in which his more complex mental processes transpire, contains some nine billion more nerve cells than does the corresponding region of the brain of an anthropoid ape.

Of especial significance in the psychic make-up of man is his vastly increased capacity for inhibition. Although not possessed by all men in equal measure and not entirely wanting in lower animals it is a distinctive feature in all human conduct. Much of any child’s education, particularly as it pertains to behavior, must be concerned with training in the exercise of proper inhibitions. He must learn to suppress certain primitive types of reaction in favor of higher ones. This applies not only to motor activities but to trains of thought as well. The essence of self-control consists mainly in ability to substitute for one impulse or idea other compensating ones. And the secret of concentration lies in being able to banish irrelevant ideas and focus on the central thought.

The Nervous System in the Main Already Staged at the Time of Birth for the Part It Must Play.—It is clear from what is known of its anatomy that in the main the central nervous system is framed to respond in certain set ways, that there are determinative elements in it which control or determine the responses, and therefore the behavior of the body. The same evidence shows also, however, in the incompleteness of many of the associations, that while the stage is all set and some of the main features of the performance are determined at the time of birth, considerable yet remains to be done toward fitting the parts together and working up the detail. Just exactly what and how much is rigidly determined no one knows.

Many Pathways of Conduction Not Established at Birth.—As we have already seen the evidence is that many of the neural pathways are not yet fully established at birth, and there is some indication that routes once opened may be altered. To what degree this has bearing on behavior is still unknown, but since neurologists attribute so much importance to the richness and the associations of the cell-outgrowths, it is evident that this increase in the number of pathways after birth with possible alternatives of connections may be a very important factor in the modification of behavior. Yet, on the other hand, we are completely in the dark as to what extent these later associations are predetermined in the earlier cells.