 6. Temperament  147
ly based concept through much of the 20th 
century. Rather, trait psychologists focused 
their attention on structural analyses, with 
the goal of creating comprehensive descrip -
tive trait taxonomies, and tended to ignore 
the etiology of the identified dimensions. 
This structural emphasis led to the criticism 
that trait psychology offered only a sterile, 
static description  of behavior, not a true ex -
planation  for it.
Mischel (1968) fanned the fires of criticism 
by suggesting that trait concepts accounted 
for relatively little variance in—and failed 
to provide even useful summary descrip -
tions of—  behavior, which ignited the long- 
standing “person–  situation debate” (Epstein 
& O’Brien, 1985; Mischel & Peake, 1982) 
that still is reverberating (Funder, 2006; see 
also Furr & Funder, Chapter 31, this vol -
ume). Although diverse issues eventually 
were incorporated into this debate, the core 
controversy revolved around two central 
questions:
1. Are traits “real” in a basic psychological 
sense or do they simply reflect cognitive 
constructions that people impose on real -
ity to increase predictability and control?
2. Are trait concepts useful predictors of 
important real-world criteria?
After nearly 20 years of theoretical and em -
pirical debate, sufficient evidence accrued to 
satisfy most researchers that the answer to 
both questions is “yes”: Traits represent real 
entities and predict important real-world 
phenomena.
Convergence of  Temperament 
and Structural Approaches
A key element in resolving the debate was 
the recognition that the major personal -
ity traits represent basic psychobiological  
dimensions of temperament (e.g., Eysenck, 
1992, 1997; Tellegen, 1985; Watson & 
Clark, 1993). The emergence of this recogni -
tion reflected several factors, three of which 
we highlight here. First, beginning in the 
late 1980s, considerable research demon -
strated that the vast majority of personality 
traits have a substantial genetic component, indicating that genotypic explanations of 
behavior underlie phenotypic descriptions of 
traits, which helped to establish that traits 
are “real” and reflect true causal influences 
on behavior rather than being mere descrip -
tive summaries. However, the connections 
between genes and their phenotypic expres -
sions have proven to be vastly more complex 
than originally envisioned; we summarize 
these data in a later section.
Second, rapidly accumulating evidence in 
the 1980s and early 1990s established that 
major dimensions of personality—  especially 
neuroticism and extraversion—  were strong -
ly associated with individual differences in 
affective experience (e.g., Meyer & Shack, 
1989; Tellegen, 1985; Watson & Clark, 
1984, 1992b, 1997). These data provided 
systematic links both to the rich literature 
on neurobiological bases of mood and emo -
tion and to temperament research, as tem -
perament has long been considered to have 
an emotional basis. Integration of research 
in the three fields of personality, mood and 
emotion, and temperament, added further to 
the evidence that traits were more than de -
scriptive summaries of behavior.
Third, after decades of seemingly indif -
ferent progress, structural research finally 
began to bear fruit, converging on a con -
sensual phenotypic taxonomy of personal -
ity traits (see Markon, Krueger, & Watson, 
2005), which we describe subsequently. This 
development enabled a more intensive focus 
on a relatively small number of consensually 
recognized traits, incorporating them into 
more complex and sophisticated concep -
tual schemes and generating more detailed, 
systematic hypotheses that helped to clar -
ify the real-world correlates of these traits 
(e.g., Watson & Clark, 1984, 1993, 1997), 
the large majority of which have proved ro -
bustly replicable (Ozer & Benet-Martínez, 
2006; Soto, 2019). Thus, the emergence of 
a temperament-  based theoretical paradigm 
elevated trait psychology to the status of 
a more mature science that—for the first 
time—  promised a comprehensive explana -
tion of human individual differences in per -
sonality. Ironically, this goal actually seems 
further away now than it did 20 years ago, 
as research has increasingly revealed how 
much we do not yet understand.