The relation between subject and object, considered biologically, is always a relation of adaptation, since every relation between subject and object presupposes mutually modifying effects from either side. These modifications constitute the adaptation. The typical attitudes to the object, therefore, are adaptation processes. Nature knows two fundamentally different ways of adaptation, which determine the further existence of the living organism the one is by increased fertility, accompanied by a relatively small degree of defensive power and individual conservation; the other is by individual equipment of manifold means of self-protection, coupled with a relatively insignificant fertility. This biological contrast seems not merely to be the analogue, but also the general foundation of our two psychological modes of adaptation, At this point a mere general indication must suffice; on the one hand, I need only point to the peculiarity of the extravert, which constantly urges him to spend and propagate himself in every way, and, on the other, to the tendency of the introvert to defend himself against external claims, to conserve himself from any expenditure of energy directly related to the object, thus consolidating for himself the most secure and impregnable position.
The fact that often in their earliest years children display an unmistakable typical attitude forces us to assume that it cannot possibly be the struggle for existence, as it is generally understood, which constitutes the compelling factor in favour of a definite attitude. We might, however, demur, and indeed with cogency, that even the tiny infant, the very babe at the breast, has already an unconscious psychological adaptation to perform, inasmuch as the special character of the maternal influence leads to specific reactions in the child. This argument, though appealing to incontestable facts, has none the less to yield before the equally unarguable fact that two children of the same mother may at a very early age exhibit opposite types, without the smallest accompanying change in the attitude of the mother. Although nothing would induce me to underestimate the well-nigh incalculable importance of parental influence, this experience compels me to conclude that the decisive factor must be looked for in the disposition of the child. The fact that, in spite of the greatest possible similarity of external conditions, one child will assume this type while another that, must, of course, in the last resort he ascribed to individual disposition. Naturally in saying this I only refer to those cases which occur under normal conditions. Under abnormal conditions, i.e. when there is an extreme and, therefore, abnormal attitude in the mother, the children can also be coerced into a relatively similar attitude; but this entails a violation of their individual disposition, which quite possibly would have assumed another type if no abnormal and disturbing external influence had intervened. As a rule, whenever such a falsification of type takes place as a result of external [p. 416] influence, the individual becomes neurotic later, and a cur can successfully be sought only in a development of that attitude which corresponds with the individual's natural way.
As regards the particular disposition, I know not what to say, except that there are clearly individuals who have either a greater readiness and capacity for one way, or for whom it is more congenial to adapt to that way rather than the other. In the last analysis it may well be that physiological causes, inaccessible to our knowledge, play a part in this. That this may be the case seems to me not improbable, in view of one's experience that a reversal of type often proves exceedingly harmful to the physiological well-being of the organism, often provoking an acute state of exhaustion.
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