Temperament

4 Physiological and Biochemical Correlates of Temperament (p.171-172)

Introduction

Most definitions of temperament, apart from their specificity, emphasize the fact that temperament has some biological background, which may be expressed in different ways. Some authors refer rather generally to the constitutional makeup (e.g., G. W. Allport, 1937), or to the fact that temperament is inherited (e.g., Buss & Plomin, 1984). Others (e.g., H. J. Eysenck, 1970; Gray, 1982a, 1982b; Kagan, 1994; Zuckerman, 1979) specify the anatomo-physiological mechanisms and/or the biochemical factors underlying temperament characteristics. Very often researchers on temperament, when discussing the biology of this phenomenon, refer to all possible levels constituting the biological foundation of temperament (e.g., H. J. Eysenck, 1990b; Rothbart, 1989a; Strelau, 1983; Zuckerman, 199 1 c).

When posing questions about the biological bases of temperament, regardless of what might be included in the term "biology," we are confronted with at least two basic difficulties. First, what do we understand by temperament? Many discussions have arisen around this question (see Chapter 1), showing that, depending on the theory that researchers have followed, the population studied (children, adults, animals), or methods used, the definition of temperament differs. Thus the question arises: What is the phenomenon we are seeking a biological basis for? Since the probability is almost nil that there is a consistent biological basis for temperament in general, whatever the definition of this concept may be, the answer to this question may not be so important for studies on the biology of temperament.

Much more important is the kind of traits (dimensions) we include in the structure of temperament. In studying the biology of temperamental traits we face a key problem so far unsolved and from this emerges the second question: What temperamental traits are to be studied, and how many of them? Recently Strelau (1991b) has identified 81 traits within the domain of temperament, and Table 6.4 in Chapter 6 presents a list of 71 traits measured by means of temperament inventories. Independent of differences in quality, these traits also have a different degree of generality. Some are very specific traits (e.g., motor impulsiveness), most of them are first-order factors (e.g., impulsivity), and some are second-order factors (e.g., extraversion).

According to Zuckerman (1992), narrower traits are probably closer to biological levels than broader ones, which might be taken as a recommendation to focus biological studies on the very specific traits and first-order factors. On the other hand, the most cogent evidence on the biology of temperament traits has been acumulated with reference to second-order factors, for example, extraversion and neuroticism.

As a matter of fact, many researchers departing from different definitions of temperament agree that extraversion is an important temperament trait, but this does not mean that authors agree on what extraversion is (e.g., Cattell, 1965; H. J. Eysenck, 1970; Gray, 1991 ; Kagan, Reznick, & Snidman, 1988). Such a state of affairs has far-reaching consequences for conclusions regarding the biology of the trait under study.