It is in nonphysical attributes that individuals display the greatest differences. Here reference is made to their variable place on a scale of energy, capacity for effective work, sensitivity, temperament, emotional responsivity, aggressivity or passivity, risk taking, ethical sense, flexibility, and tolerance to change and stress. The composite of these qualities constitutes the human personality or character. A current model of personality structure identifies 5 dimensions, which account for the covariation of most personality traits: (1) neuroticism versus emotional stability; (2) extraversion versus introversion; (3) openness to experience versus aversion to change; (4) agreeableness versus irascibility; and (5) conscientiousness versus unscrupulousness, and all five of these are heritable, as discussed in Chap. 50.
In the formation of personality, especially the part concerned with feeling and emotional sensitivity, basic temperament surely plays a large part. By nature, some children from the beginning seem to be happy, cheerful, and unconcerned about immediate frustrations; others are the opposite. By the third month of life, Birch and Belmont recognized individual differences in activity–passivity, regularity–irregularity, intensity of action, approach–withdrawal, adaptivity–unadaptivity, high–low threshold of response to stimulation, positive–negative mood, high–low selectivity, and high–low distractibility. Ratings at this early age were found to correlate with the results of examinations made at age 5 years. Kagan and Moss recognized the trait of timidity as early as 6 months of age and noted that it persists lifelong.
The more common aspects of personality, that is, anxiety or serenity, timidity or boldness, the power of instinctual drives and need of satisfaction, sympathy for others, sensitivity to criticism, and degree of disorganization resulting from adverse circumstances, are presumed to be genetically determined. Identical twins raised apart are remarkably alike in these and many other personality traits (and have the same IQs, within a few points). Scarr and associates have also demonstrated the strong genetic influence on personality development. The related subject of the development of a moral sense that can be said to be part of an individual’s personality has been subject to several competing theories. The interested reader is referred to Damon’s summary of the topic.
Chapter 50 discusses disorders of personality and the genetic predisposition to certain personality traits further.
Social behavior, like other neurologic and psychologic functions in general, depends to a great extent on the development and maturation of the brain. Involved also are genetic and environmental factors, for one cannot adapt to society except in the presence of other people; that is, social interaction is necessary for the emergence of many basic biologic traits. The roots of social behavior are traceable to certain instinctive patterns that are progressively elaborated by conditioned emotional reactions. In the long series of human interactions—first with parents, then with siblings and other children, and finally with a widening circle of individuals in the classroom and community, the capacity to cooperate, to subjugate one’s own egocentric needs to those of the group, and to lead or be led appear as secondary modes of response (i.e., secondary to some of the basic impulses of anger, fear, self-protection, love, and pleasure). The sources of these social reactions are even more obscure than those of temperament, character, and intelligence.
In children, difficulty in social adaptation tends first to be manifest by an inability to take their places in a classroom. However, the greatest demands and frustrations in social development are likely to occur in late childhood and adolescence. The development of adult gonadal function and the further evolution of psychosexual impulses create a bewildering array of new challenges in social adaptation. These types of social adjustments continue as long as life continues. As social roles change, as intellectual and physical capacities first advance and later recede, new challenges demand new adaptations.