146 II. BIOLOGICAL  FOuNDATIONS
sonality dimensions of the modern theorist 
Hans Eysenck, neuroticism (vs. emotional 
stability) and extraversion, which are found 
in all major models of temperament and per -
sonality. Specifically, the stable extravert is 
sanguine, the unstable extravert is choleric; 
the unstable introvert is melancholic, and 
the stable introvert is phlegmatic (Eysenck 
& Eysenck, 1975).
A Brief Modern History 
of Temperament  Research
In addition to the notion that temperament 
reflects biologically based individual dif -
ferences in emotional responding, modern 
temperament theories also have incorpo -
rated Allport’s idea that these biological dif -
ferences are innate and form the foundation 
upon which mature personality develops. 
Seminal in childhood temperament research, 
Thomas, Chess, and Birch’s (1968; Thomas 
& Chess, 1977) nine-  dimensional structure 
promoted the view that childhood behavior 
is structured, measurable, and systematically 
related to later personality development. Nu -
merous spin-off measures spanned the de -
velopmental range from birth through ado -
lescence. Most notably, Eysenck (1967) and 
Strelau (1983) offered early models of adult 
temperament derived from Pavlov’s theory 
of central nervous system (CNS) proper -
ties. Not widely known in the United States, 
Strelau’s work (Strelau & Zawadzki, 1995; 
Oniszcenko et al., 2003) has been quite in -
fluential among European temperament re -
searchers, and both models spawned numer -
ous learning-  based experimental studies.
J. Gray (1982, 1987) also offered a biolog -
ical model of temperament that overlapped 
notably with Eysenck’s work. Based largely 
on pharmacological studies with animals, J. 
Gray’s work strongly influenced theorizing 
about adult personality or temperament di -
mensions. J. Gray (Wilson, Barrett, & Gray, 
1989) and others (most notably, Carver & 
White, 1994) developed self-  report ques -
tionnaires to assess J. Gray’s hypothesized 
dimensions, but the former’s measures “bore 
only a partial resemblance” (Wilson, Gray, 
& Barrett, 1990, p. 1037) to the constructs 
they were designed to measure, and the lat -ter’s scales align closely with Eysenck’s neu -
roticism and extraversion (e.g., Jorm et al., 
1999) rather than with Gray’s dimensions, 
which Gray viewed as 45 degrees rotated 
from Eysenck’s (e.g., J. Gray, 1987). Thus, 
relatively little direct testing of J. Gray’s 
initial model was conducted with people 
due largely to these difficulties in assessing 
the hypothesized neuropsychological sys -
tems. By contrast, Buss and Plomin (1975) 
articulated a temperament model that had 
relatively little theoretical impact but was 
widely used in research, owing to the EASI 
Temperament Survey, which they developed 
to measure their four proposed dimensions 
of emotionality, activity, sociability, and im -
pulsivity.
In various ways, these early efforts were 
instrumental in beginning to link biological 
variables with temperament dimensions and 
their adult personality outgrowths, and they 
now are starting to bear fruit in the form 
of (1) better measurement models (e.g., De 
Clerq et al., 2014; Rothbart & Bates, 2006; 
Shiner, 2015), (2) a major revision of J. 
Gray’s theory that is “biologically more ac -
curate” (Revelle, 2008, p. 509), and (3) more 
sophisticated and complex theoretical mod -
els emerging in the developing fields of cog -
nitive, affective, and personality neurosci -
ence (e.g., Corr & McNaughton, 2012). The 
original version of this chapter in the second 
edition (Clark & Watson, 1999) contained 
a substantial section on biological models 
of temperament. However, because the lit -
erature on this topic has exploded in the 
21 years since then, we cannot possibly do 
justice to the topic. Instead, we direct inter -
ested readers to three particularly relevant 
chapters elsewhere in this volume: De  Young 
(Chapter 8), on the neurobiological basis of 
personality; Krueger and Johnson (Chapter 
9), on behavioral genetics and personality; 
and de Moor (Chapter 10), on the molecular 
genetics of personality.
The Structural “Trait” Approach
In contrast to developmentalists and Euro -
pean temperament researchers, American 
personologists showed relatively little inter -
est in studying temperament as a biological -