fei75766_ch14_435-462.indd 458  02/06/20 01:10 PM
Part V    Biological/Evolutionary Theories458
Fourth, auseful theory hasthepower toguide the actions of practitioners, and
onthiscriterion, biological theories rankrelatively low.Although these theories doa
good jobofexplaining theorigins ofpersonality differences, theydonoteasily lend
themselves topractical guides forteachers, parents, andevencounselors. Onthis
criterion, biological theory rates relatively low.
Aretraitandfactor theories internally consistent? Again, therating must be
equivocal. Thetheory ofEysenck isamodel ofconsistency, butwhen compared tothe
Five-Factor model, Eysenck’s model issomewhat inconsistent. Eysenck remained con-
vinced thathisGiant Three factors weresuperior totheBigFivemodel. Thisinconsis -
tency presents aproblem, especially because factor analysis isaprecise mathematical 
procedure andbecause factor theories areheavily empirical.
Thefinalcriterion ofauseful theory isparsimony. LikeMcCrae andCosta’s 
Five-Factor Model, Eysenck’s model ofpersonality isalsobased onfactor analysis 
andtherefore provides averyparsimonious explanation ofpersonality. Indeed, with
onlythree major dimensions, Eysenck’s model isevenmore parsimonious thanthe
Five-Factor approach.
 Concept of Humanity
On the determinism versus free choice  dimension, Eysenck’s theory sides 
somewhat toward the deterministic view, but only slightly. Biological founda -
tions are difficult to change, but as the diathesis-stress models make clear, 
both biology and environment are needed to create final personality quali -
ties in an individual. 
Regarding optimism versus pessimism , Eysenck is mostly silent, but on 
teleology versus causality , he comes down on the side of causality. Recall the 
model in Fig  ure 14.6, where the chain of causality runs from DNA to limbic 
system to traits to proximal consequences and finally to distal consequences. 
On the question of conscious versus unconscious determinants of behav -
ior, Eysenck’s approach leans toward unconscious determinants insofar as 
people are mostly incapable of being aware of how genetics and brain pro -
cesses affect their behavior and personality. Regarding the issue of biological 
versus social influences , it may be somewhat surprising to say, but in fact, 
Eysenck very much argued for “both-and”—both nature and nurture. Biology 
may set the floor and ceiling of our behavior, but environment is needed to 
determine whether we will be closer to the floor or ceiling of our potential. 
On the dimension of individual differences versus similarities,  biologi -
cal theory leans quite a bit toward individual differences. Biological, brain, 
and genetic differences focus on the uniqueness of individuals. Eysenck 
(1981), for example, wrote that “people are above all individuals” (p. xi). And 
yet at the same time, biological theory also demonstrates the commonality 
we all share as members of a single species. In that we are all members of 
the same species, we expect to see and do see commonality in personality 
structure the world over.Final PDF to printer