General Developmental Theories -Temperament theory
Seven major theories of development are listed in Table 1-2, along with key concepts and criticisms of each theory. These theories, along with their applications, are described in detail in the sections that follow.
Since the “human bile” theories of ancient Greeks, scholars have speculated that persons are born into the world with varying predispositions to behave in particular ways, called traits. Trait theorists have postulated a variety of dispositional tendencies, from Eysenck’s neuroticism and extraversion to the “Big Five” traits of agreeableness, openness, extraversion, neuroticism, and conscientiousness. In developmental inquiry, temperament theory has received the greatest attention. It has been hypothesized that infants are born with biologically based temperaments that vary on a continuum from difficult to easy. This trait is evidenced in ease of early care, including feeding, soothing, and cuddling. As children grow older, these differences are evidenced in ease of manageability (eg, the temper tantrums of 18-month-old children and the behavior difficulties of the preschool period). The trait of difficultness has been hypothesized as a risk factor for conduct disorder. Empirical studies have found significant but modest support for this hypothesis. Prospective studies indicate that infants characterized as difficult are indeed at risk for conduct problems in the early school years, but the relation is somewhat weaker (although still present) for predictions from infancy to adolescence.
A different temperament theory, proposed by Kagan, has focused on a continuum of biological inhibition as the marker variable. Some infants regularly withdraw from novel social stimuli (inhibited pattern) whereas others seek out social stimulation (uninhibited pattern). Optimal levels of inhibition may fall between these extremes. Highly inhibited infants exhibit separation anxiety from parents and are likely to grow into shy, fearful, and withdrawn children. They are thought to be at risk for panic disorder in adulthood. Most individuals demonstrate an increase in heart rate and stabilization of heart rate variability in response to a stress challenge. Individuals vary systematically in the degree to which the hypothalamus, pituitary gland, and adrenal gland (HPA) (called the HPA axis) respond with glucocorticoid secretion during stress. Inhibited children have a lower threshold of sympathetic nervous system response and display a greater rise and stabilization of heart rate than uninhibited children exhibit. This pattern acts as a trait-like temperamental characteristic throughout life that may be associated with symptoms of anxiety.
Another postulate of temperament theories is that temperament elicits environmental treatment that perpetuates behavior consistent with that temperament. For example, it is hypothesized that “difficult” children elicit harsh discipline, which exacerbates difficult behavior, whereas inhibited children seek secure environments that pose minimal challenge and risk. Plomin has shown through twin and adoption studies that environmental experiences have a heritable component; that is, inherited genes lead either to behavior patterns that elicit environmental reactions or to behaviors that seek particular environments, a phenomenon known as niche-picking.
Applications of the Theory
Most temperament theorists recognize the importance of both inherited and environmental sources of development, so this theory has spawned empirical research directed toward understanding how these forces interact. It may be that infants with a particular temperament will develop more favorably under certain environmental conditions than others, and the task of inquiry is to identify optimal temperament- environment matches. Researchers are examining whether temperamentally difficult infants (or highly inhibited infants) develop more favorably under conditions of environmental restraint and structure or flexibility and freedom.
Another application has been to encourage research on the process through which genetic effects may operate on human development, thus informing the age-old debate between nature and nurture influences on human behavior.
Criticisms of the Theory
One problem with research on temperament theory has been the reliance on parents for assessments of temperament. Parents may be biased or inaccurate, or they may lack a broad base of knowledge of other infants. A parent’s perceptions about his or her child may be legitimate factors in the child’s development, but these perceptions confound information about the child’s actual behavior with the parent’s construal of the behavior. More direct observational measures of behavior have been developed to assess temperament, as have measures of biological functions, including heart rate reactivity, cortisol secretions, and skin conductivity. These measures also show some stability across time and some predictive power, but the number of studies is small and the statistical effects are weak.
Another problem is the difficulty of distinguishing genetic-biological features from reactions to environmental treatment. A 6-month-old infant brings both a genetic heritage and a history of environmental experiences to current interactions. Even biological measures (eg, resting heart rate, cortisol levels) have a partial basis in past social exchanges, so that the task of sorting genetic from environmental sources in bio-behavioral measures is difficult.