The science of life : fully illustrated in tone and line and including many diagrams

HUMAN BEHAVIOUR AND THE HUMAN MIND

Birth-injuries, childish illness, remediable defects in eye or ear, under-feeding, fear, and unhappiness—all these can hamper the development of intelligence just as a favourable environment can help it on; but the single cause which far outweighs all others in determining the degree of intelligence is the combination of genes with which the child is born. This is seen with especial clearness in those numerous cases—like the Cecils, or the Darwins—where intellectual ability runs in families. It is also well brought out by intelligence tests on children brought up from their earliest years in orphanages ; in spite of the uniformity of their upbringing, they show as wide a range of capacity, as measured by intelligence tests or in other ways, as do other children.

Besides these differences in general intelligence, there are many differences in special capacities; and these are even more exclusively determined by heredity. The most obvious of such special gifts are the mathematical and the musical. Pascal as a mere child begged to be allowed to learn about numbers, but his father insisted that this must wait until his education in languages and history was more advanced. But his mathematical bent was not to be denied ; when he was still a mere child, his father found him busied with problems in geometry. Unaided, he had already worked out for himself a series of the theorems of Euclid.

At the age of four, Mozart could play minuets ; at five, he had already composed a number of little pieces, and gave his first public performance. So great was his passion for music that he slipped out of bed to practise in the middle of the night.

At the other end of the scale, we have men of the highest intellect who cannot tell God Save the King from Pop Goes the Weasel, and others to whom any mathematics beyond the simplest arithmetic is a closed book.

Another important difference is between brain and hand, intellectual and motor ability. Everyone knows how some children, stupid at book-learning, excel in carpentry or have an uncanny knowledge of mechanical toys and the insides of motor-cars ; while others who are near the top of their class are both awkward with their hands and uninterested in handwork. Statistical tests seem to show that this is not exceptional. Highly intelligent children are, on the average, a little behindhand in their motor abilities, while those who are exceptionally gifted with their hands are, as a group, a

shade below the average in their intelligence. Plenty of exceptions exist, but the tendency is there.

With this difference between brains and hands we are introduced to something newa difference in quality of disposition rather than in quantity of some single endowment. Early in the present century, Jung, the psycho-analyst, formulated a broad distinction between two outstanding types of personality. Other attempts at classifying types of mind had been made before himthe most celebrated perhaps was William James’s division of the human race into ““tender-minded”” and ‘ tough-minded ” —but Jung was the first to attack the problem systematically in the light of modern knowledge. One type he called introvert—turned in upon itself; the other extrovert—turned outwards towards the outer world. The one is more interested in his own inner being, the other in the practical give-and-take of life. To the one the outer world provides the necessary material out of which the inner constructions of thought may be built ; to the extrovert, the inner construction is of value as enabling him to live more fully in the world of people and things around him. The introvert tends to be solitary, shy, given to speculation and imagination, often troubled about himself, his future, his relation to the universe at large. The extrovert, on the contrary, tends toa balanced expansiveness and sociability which contrasts with the somewhat fitful liveliness of the introvert ; he makes friends easily, has little embarrassment about such public performances as acting or singing, which are often a torture to the introvert, is bored with anything abstruse or speculative, lives much more in the present.

There is no doubt that this picture has a great deal of truth in it. One can often see this turning of the mind inwards and outwards exemplified in two members of the same family, even at an early age. It is further likely that the lack of correspondence between ability of hand and of brain which we have just noted is concerned with a difference in psychological type. The introverted child is more interested in things of the mind, takes less trouble with practical handwork ; and vice versa with the extrovert. There is also the fact, elicited during the War, that dissociation and hysteria are the normal outcome of conflict in the extrovert, while in the introvert similar conflicts are likely to end in repression and neurasthenia. In fact, the fundamental basis of the difference between the two types

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