In the same family one child is introverted, the other extraverted. Since the facts show that the attitude-type is a general phenomenon having an apparently random distribution, it cannot be a matter of conscious judgment or conscious intention, but must be due to some unconscious, instinctive cause. As a general psychological phenomenon, therefore, the type antithesis must have some kind of biological foundation.
The fact that children often exhibit a typical attitude quite unmistakably even in their earliest years forces us to assume that it cannot be the struggle for existence in the ordinary sense that determines a particular attitude. It might be objected, cogently enough, that even the infant at the breast has ato perform an unconscious act of psychological adaptation, in the at the mother's influence leads to specific reactions in the child. This argument, while supported by incontestable evidence, becomes rather flimsy in face of the equally incontestable fact that two children of the same mother may exhibit contrary attitudes a t an early age, though no change in the mother's attitude can be demonstrated. Although nothing would induce me to underrate the incalculable importance of parental influence, this familiar experience compels me to conclude that the decisive factor must be looked for in the disposition of the child. Ultimately it must be the individual disposition which decides whether the child will belong to this or that type despite the constancy of external conditions. Naturally I am thinking only of normal cases. Under abnormal conditions, i.e., when the mother's own attitude is extreme, a similar attitude can be forced on the children too, thus violating their individual disposition, which might have opted for another type if no abnormal external influences had intervened. As a rule, whenever such a falsification of type takes place as a result of parental influence, the individual becomes neurotic later, and can be cured only by developing the attitude consonant with his nature.
As to individual disposition, I have nothing to say except that there are obviously individuals who have a greater capacity, or to whom it is more congenial, to adapt in one way and not another. It may well be that physiological causes of which we have no knowledge play a part in this. I do not think it improbable, in view of one's experience that a reversal of type often proves exceedingly harmful to the physiological well-being of the organism, usually causing acute exhaustion.