436 Part V Biological/Evolutionary Theories
thinking, motives, drives, and even their dreams. Most of these theories, as you
have seen in Parts I to III of the current book, assume that personality is caused
by environmental events alone and seldom even mention any biological compo-
nent. Evolutionary theory, however, assumes that the true origins of these traits
reach far back in ancestral times. The true origin of personality is evolution, mean-
ing that it is caused by an interaction between an ever changing environment and
a changing body and brain. Evolutionary theory is one of the few recent theories
of personality that attempts once again to explain the grand view of human
personality—its ultimate origins as well as its overall function and structure. “Evo-
lutionary meta-theory, properly conceived, provides for personality psychology the
grand framework it seeks, and which has been missing almost entirely from its
core formulations” (Buss, 1991, p. 486).
As you have seen throughout this book, personality is primarily concerned
with how individuals differ consistently in what motivates them and how they act
and think. Evolution also starts with the assumption that individual members of
any species differ from one another. In this sense, the two would appear to be
perfect partners. Given the fact that both personality and evolution have individual
differences as their starting point, you would have thought that the marriage of the
two would have been obvious and happened soon after Darwin suggested it would
in the mid to late 19th century.
Yet few took up the challenge and the marriage did not happen until the
1990s. In fact, as two of the main proponents of evolutionary psychology—Tooby
and Cosmides—pointed out early in the marriage, there was a serious problem:
natural selection typically works to lessen individual differences insofar that suc-
cessful traits and qualities become the norm and less adaptive traits die out. Over
long periods of time, nature is selecting the same trait. To put it most clearly, there
is a paradox here: “If natural selection winnows out maladaptive traits and over
the long-term produces a universal human nature then how can individuals consis-
tently differ in their disposition to think and behave (i.e., have personality)?”
(Tooby & Cosmides, 1990). Human adaptations should remain universal and
species-typical, meaning there should not be significant differences between indi-
viduals. Indeed, Tooby and Cosmides argue that by definition if a trait shows
significant individual differences it cannot be an adaptation, because by definition
adaptations are species typical. To be clear, Tooby and Cosmides were not so much
denying the existence of personality as they were denying that it was an adaptation.
And yet few deny that personality and individual differences exist. How do we
explain this paradox?
Indeed, early in its development the field of evolutionary personality psy-
chology itself was divided over how to solve this paradox. Some leading
evolutionary psychologists argued for two solutions: personality differences were
either “noise” or they were perhaps “by-products” of evolved adaptive strategies
(Tooby & Cosmides, 1990). More recently, however, other theorists have made
the case for personality traits being something more than noise or by-products,
namely adaptations (D. Buss, 1991, 1999; MacDonald, 1995; Nettle, 2006; Nich-
ols, Sheldon, & Sheldon, 2008). Because David Buss was the first and most
prominent theorist to take up the cause of developing an evolutionary theory of
personality, we focus on his theory. Later in the chapter, we briefly review a few