1) Evolutionary theory assumes that personality traits have evolved over time through natural selection to help solve adaptive problems related to survival and reproduction. 2) David Buss developed one of the first evolutionary theories of personality, proposing that personality traits are psychological mechanisms that evolved to deal with specific adaptive problems like obtaining food, avoiding danger, and competing for mates. 3) Buss argued that consistent individual differences in personality traits can be explained as adaptations if the traits helped our ancestors solve adaptive problems in their environments and were heritable.

1. Evolutionary Theory of Personality
From the beginning to the end of the 20th century personality
theories went from
grand theories that attempted to explain all people at all times
to smaller, more targeted
theories that focused on single aspects of personality, such as
the structure of
personality or the nature of self. Starting with Freud in the early
1900s, theories of
personality had attempted to understand people’s conscious and
unconscious thinking,
1 Herbert Spencer published Principles of Psychology in 1855,
four years before Darwin’s Origins , in
which he argued for a biological and even evolutionary view of
human thought and behavior.
424 Part V Biological/Evolutionary Theories
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
component. Evolutionary theory,
however, assumes that the true origins of these traits reach far
back in ancestral times.
The true origin of personality is evolution, meaning 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. “Evolutionary meta-theory,
properly conceived, provides

2. 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 they
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 successful 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 consistently differ in their
disposition to

3. 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 individuals. 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 fi eld of evolutionary
personality psychology
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; Nichols, Sheldon, & Sheldon, 2008). Because
David Buss was
the fi rst 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,
Chapter 15 Buss: Evolutionary Theory of Personality 425

4. we briefl y review a few of the extensions by neo-Bussian
theorists. The essence
of Buss’s theory of personality revolves around adaptive
problems and their
solutions or mechanisms. Before discussing adaptations and
their solutions, let
us fi rst review the nature and nurture of personality.
The Nature and Nurture of Personality
Recall that personality is all about consistent and unique
differences between individuals
in how they think and behave. The question quickly becomes,
“What
causes these individual differences?” As with all questions
about human behavior
it comes down to two fundamental answers: nature and/or
nurture. That is, behavior
and personality are caused by either internal qualities or
external-environmental
ones. It is easy to see, however, that this dichotomy is a false
one. Internal states
and processes, from biological and physiological systems to
personality traits,
come about from input from the environment. Neither can
function without the
other, although the history of psychology is largely a history of
nature versus
nurture. On the one side, there is what Buss called the
fundamental situational
error, or the tendency to assume that the environment alone can
produce behavior
void of a stable internal mechanism. “Without internal
mechanisms there can be
no behavior” (D. Buss, 1991, p. 461). On the other side, there is
what social
psychologists have called the fundamental attribution error to
describe our tendency

5. to ignore situational and environmental forces when explaining
the behavior
of other people and instead focus on internal dispositions.
Indeed, each of these
views alone is incomplete because there is no such thing as
purely internal or
purely external explanations of behavior. The two must be
involved and interact
in any behavior.
Evolved mechanisms are good examples of the interaction of
nature and
nurture because they only exist in response to and with input
from the environment.
There is no split between biological and environmental.
Environment does
not affect behavior without a mechanism to respond. Evolution
in general is
inherently an interaction between biology and environment
(nature and nurture).
All biological structures and by extension all psychological
systems have come
about only in the context of a particular environment and what
was happening
in that environment. During early stages of evolution, some
individuals had
qualities that worked in that environment at that time and hence
were more
likely to survive and reproduce. One of the fundamental
assumptions of evolutionary
theory of personality is that these adaptive qualities include
consistent
and unique dispositions to behave in particular ways in
particular contexts, in
other words, personality traits.
Adaptive Problems and their

6. Solution
s (Mechanisms)
Ever since Darwin, it has been clear that all life forms are
confronted with two
fundamental problems of adaptation, namely survival (food,
danger, predation, etc.)
and reproduction. In order to survive any living thing has to
deal with what he called
the “hostile forces of nature,” which include disease, parasites,
food shortages, harsh
climate, predators, and other natural hazards (D. Buss, 1991).
Individuals who solve
426 Part V Biological/Evolutionary Theories
these problems most effi ciently and effectively are most likely
to survive, and survival
is a precondition for reproduction.
The process of evolution by natural selection has produced
solutions to these
two basic problems of life and they are called mechanisms .
More specifi cally,
mechanisms
• operate according to principles in different adaptive domains

7. • number in the dozens or hundreds (maybe even thousands)
• are complex solutions to specifi c adaptive problems (survival,
reproduction)
Each mechanism works specifi cally on the problem it solves
and not other ones.
For example, sweat glands solve the problem of regulating body
temperature but
do nothing for disease or wounds. Psychological mechanisms
operate by converting
input into particular actions or decision rules that help solve
these adaptive
problems (D. Buss, 1991).
There are two specifi c main classes of mechanism, namely
physical and
psychological. Physical mechanisms are physiological organs
and systems that
evolved to solve problems of survival, whereas psychological
mechanisms are
internal and specifi c cognitive, motivational, and personality
systems that solve
specifi c survival and reproduction problems.
Anatomical and physiological mechanisms are often shared by
many species,
whereas psychological mechanisms are often more specifi c to
species. Evolutionary

8. biology focuses on the origin of physical mechanisms, whereas
evolutionary psychology
focuses on the origin of psychological mechanisms. Indeed, a
major contribution
of evolutionary psychology to evolutionary theory is the
introduction and
development of psychological mechanisms.
Examples of survival and reproduction problems and their
various physical
and psychological solutions are presented in Table 15.1 (Buss,
1991). For example,
animals of different species have evolved similar sensory
systems. In most vertebrates,
and mammals in particular, these take the form of eyes, ears,
nose, skin,
and tongue. Senses are adaptive in that they function to take in
different kinds of
information from the outside world and allow the organism to
respond appropriately.
Sensory mechanisms differ between species of animals. Dogs
for instance,
hear sounds with pitches between 10 and 35,000 cycles per
second (Hertz), whereas
humans only hear sounds in the 20 to 20,000 cycles per second
(Hertz) range.

9. Humans, however, evolved photoreceptor cells (cones) in the
retina that are sensitive
to three different wavelengths of light, namely red, green, and
blue (Jacobs &
Nathans, 2009). Dogs, like most other mammals, evolved cones
sensitive to only
two wavelengths, namely blue and green (Neitz, Geist, &
Jacobs, 1989). Humans,
in other words, have better color vision than dogs, but dogs hear
(and smell) much
better than humans. Another physical mechanism is the immune
system, which
evolved in response to the problem of parasites and disease, just
as blood clotting
developed to solve the problem of dying from wounds or injury.
An example of a reproductive problem is same-sex competition,
which stems
from the fact individuals must compete with members of the
same sex for access
to reproduce with the opposite sex. The problem, therefore, is
same-sex competition,
or in Buss’s words: “besting members of one’s own sex to gain
access to desirable
members of the opposite sex” (1991, p. 465). One solution, but
by no means the

10. Chapter 15 Buss: Evolutionary Theory of Personality 427
only solution, to reproduction is dominance. Individuals who
successfully compete
against same sex members of their species are the dominant
members of a group
and as such they are generally successful at many specifi c
problems, such as acquiring
resources, negotiating social hierarchies, forming successful
alliances, and successfully
courting a potential mate (D. Buss, 1988, 1991).
Psychological mechanisms have behavioral consequences,
tactics, and actions
associated with them (Buss, 1991, 1999). For example, intrasex
competition results
from a dominant member in a group being a leader and is a
result of someone who
could successfully negotiate his or her place in a hierarchy, fend
off enemies, and
attract mates. The main job of an evolutionary model of
personality is to describe,
study, and explain these enduring psychological mechanisms.
Evolved Mechanisms
Again, psychological mechanisms are internal processes that
help solve problems
of survival and/or reproduction. Psychological mechanisms

11. relevant to personality
can be grouped into three main categories:
• goals/drives/motives
• emotions
• personality traits
T A B L E 1 5 . 1
Examples of Evolutionary Problems and Their