 1. The Evolution of Human Personality 5
is that of “divine creation,” the idea that a 
deity created humans in all of their glorious 
nature. Another theory is that extraterres -
trial organisms planted the seeds of life on 
earth, and that these seeds were transformed 
by some evolutionary process over millions 
of years into humans. Neither divine cre -
ation nor seeding theory have many propo -
nents among modern scientists. Indeed, only 
one theory of origins, albeit with modifica -
tions and extensions, has held sway among 
scientists over the past century and a half—
the theory of evolution by selection.
Although it is widely misunderstood, the 
theory of evolution by selection is remark -
ably simple. First, individuals differ in a va -
riety of ways. Second, some of these variants 
are heritable—  passed down from parents to 
children. Third, some of these variants influ -
ence survival and reproduction recurrently 
over generations. Fourth, those variants that 
contribute to greater reproduction (relative 
to extant competing variants), directly or 
indirectly, are passed down to succeeding 
generations in greater numbers than other 
variants that lead to comparatively lower 
reproduction. Fifth, over many generations, 
variants associated with greater reproduc -
tion continue to increase in relatively fre -
quency in the population, thereby displacing 
other, less successful variants and eventually 
spreading to most or all members of the spe -
cies. This selective process, occurring over 
vast expanses of time and space, is respon -
sible for the “design” of all organisms.
Selection, of course, is not the only causal 
process that produces change over time. Ge -
netic drift, sudden catastrophes, such as a 
meteorite hitting the earth, and other pro -
cesses certainly produce change and must 
be included in any comprehensive evolution -
ary account. Selection, however, is gener -
ally regarded as the most important causal 
process, since it is the only known causal 
process  that can produce complex function -
al design, at some basic level of analysis . A 
meteorite may have caused the extinction 
of dinosaurs, and perhaps even opened up 
new niches for the explosive evolution of 
mammals, but such catastrophic events can -
not create the complex functional design 
that characterized dinosaurs or any other 
organisms. Whereas unpredictable catas -
trophes are important in understanding the evolution of life on earth, no known causal 
process other than selection can produce 
the complex functional design that charac -
terizes all organisms (see Buss, Haselton, 
Shackelford, Bleske, & Wakefield, 1998, for 
a more detailed discussion of these issues).
For this reason alone, any psychological 
theory, including any theory of personal -
ity, must fit within a broader evolutionary 
framework. To put it differently, all psy -
chological theories are implicitly or explic -
itly evolutionary (Symons, 1987). Although 
many psychologists fail to specify their as -
sumptions about the evolution of human 
nature (keeping those assumptions implicit), 
not one has ever proposed a psychological 
theory that has presumed some other causal 
process to be responsible for creating human 
nature.
Despite this, most personality psycholo -
gists have entirely ignored evolutionary pro -
cesses in their domains of study. Motive ap -
proaches to personality, which would seem 
to have obvious evolutionary relevance, 
historically have ignored evolution. Re -
searchers who study the “self” have cre -
ated mini-  theories such as self-  verification 
theory, self-  enhancement theory, and social 
identity theory in a theoretical vacuum, un -
informed by the causal processes that cre -
ated the psychological mechanisms involved 
or the functions of those mechanisms. Psy -
chologists who study traits and trait tax -
onomies typically have the goal of identi -
fying the statistical structure of individual 
differences, without an interest in how and 
why evolution might have shaped that par -
ticular structure of personality. Description, 
of course, is often an important first step. 
As evolutionary biologist George Williams 
(1966, p. 20) noted, “Many sciences develop 
for a time as exercises in description and 
empirical generalization. Only later do they 
acquire reasoned connections within them -
selves and with other branches of knowl -
edge. Many things were scientifically known 
about human anatomy and the motions of 
the planets before they were scientifically 
explained.”
We suggest that the time is ripe for the 
scientific maturation of personality psychol -
ogy. We present in the remainder of this 
chapter a powerful set of conceptual tools 
that an evolutionary framework can offer 