"The temperamental characteristics of a human adult are the end products of a developmental process in which original endowment, maturation, and learning have all entered in important degree."
One of the major assumptions underlying the construct of temperament is that it is constitutional-biologically based (Slabach, 1991). Genetic factors are a common denominator in literature dealing with the biological roots of temperament and correlates of temperament such as neuroanatomy, neurophysiology, and endocrinology. As Plomin (1994) suggests, it seems clear,
This link between genotype and the environment is supported by Eyesnk (1991) who concludes that "genetic factors cannot act directly on behavior; there must be an intervening link between genes and chromosomes on the one hand, and social behavior on the other" (p.87). Mehrabian's (1991) contention is that genetic factors determine at least 50% of temperament traits, with the balance learned in the first dozen or so years of life" (p.83). This early emergence of temperament is also supported by the research of Buss and Plomin (1986):
Studies of twins by researchers Torgersen and Kringlen (1973) show, "a strong genetic influence on temperament, and that future studies on this topic should not ignore the significance of the genetic influence" Thomas & Chess, 1977, p.133). Data from the study also indicates that parental attitudes and functioning, as shaped by the sex of the child or special concerns for a premature infant, at the very most have a modest etiological influence on temperament. The authors also note,
Kroner (1972), in an untested study, sugests that behavioral sex differences in the neonate may result from the action of hormones in utero in sensitizing the organism's central nervous system. Calkins (1994) examined the biological-temperament link in several studies using measures of regional brain electrical activity in infants and young children. Specifically, Calkins examined the relationship between the pattern of brain electrical activity found in the frontal scalp, leads and the dimensions of temperament that were described by other resarchers as being approach-withdraw or sociability-inhibition. Calkins also notes similar research by Fox regarding brain activity as measured by EEG and hemispheric dominance.
These studies are not without their critics. Fahrenberg (1991), in reviewing the research on psychophysiological measurement of temperament, concludes that biologically oriented personality researchers,
Zukerman (1991) points out that while heredibility of personality traits is much higher than most psychologists dreamed of 20 years ago, it must be emphasized that personality traits are not directly inherited, but are only manifestations of particular combinations of inherited biological traits" (p.142).
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Peter L. Heineman
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