EvolutionarypersonalitypsychologyReconcilinghumannatureandindividualdifferences.pdf

Personality and Individual Differences 48 (2010) 509–516
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Personality and Individual Differences

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / p a i d
Review

Evolutionary personality psychology: Reconciling human nature
and individual differences

Richard L. Michalski a,*, Todd K. Shackelford b

a Department of Psychology, Hollins University, PO Box 9687, Roanoke, VA 24020, USA
b Department of Psychology, Florida Atlantic University, 2912 College Avenue Davie, Florida 33314, USA
a r t i c l e i n f o

Article history:
Received 6 August 2009
Received in revised form 9 October 2009
Accepted 23 October 2009
Available online 8 February 2010

Keywords:
Evolutionary psychology
Personality psychology
Individual differences
0191-8869/$ – see front matter � 2009 Elsevier Ltd. A
doi:10.1016/j.paid.2009.10.027

* Corresponding author.
E-mail address: [email protected] (R.L. Micha
a b s t r a c t

Personality, from an evolutionary perspective, represents a meta-category of the output of a suite of spe-
cies-typical, relatively domain-specific, evolved psychological mechanisms designed in response to the
social adaptive problems recurrently faced by our ancestors. This conceptualization of human personality
provides for novel and valuable reinterpretations of several areas of personality psychology including
personality consistency, individual differences in personality, sex differences and similarities, and con-
textual determinants of personality. Explaining human personality from an evolutionary perspective
has led to discoveries about the function of social information conveyed through standings on the Big-
Five personality dimensions and discoveries in topics such as social anxiety, jealousy, altruism, aggres-
sion, psychopathology, mate preferences, and desire for sexual variety. We argue that limitations of
the application of evolutionary theory to personality science are surmountable and that, despite these
limitations, large strides have been and will continue to be made through a union of personality science
and evolutionary science.

� 2009 Elsevier Ltd. All rights reserved.
1. Introduction existence of personal constructs (Kelly, 1955), needs (Freud,
The ontogeny, structure, and processes of human personality
and of human nature, more generally, have been crafted over hun-
dreds of thousands of generations by natural and sexual selection.
There is no scientifically viable alternative for understanding the
historical origins of human personality. The meta-theory of evolu-
tion by natural and sexual selection (Darwin, 1859/1958; Darwin,
1871) has been supported, at various theoretical levels, by thou-
sands of investigations spanning the disciplines of, for example,
biology, ecology, medicine, anthropology, psychology, and ethology
(see, e.g., Barkow, Cosmides, & Tooby, 1992; Daly & Wilson, 1983;
Krebs & Davies, 1987; Smith & Winterhalder, 1992; Strickberger,
1990; Trivers, 1985). The application of evolutionary theory to
these disciplines has yielded new insights, generated new lines of
research, and in some cases, added a much needed theoretical foun-
dation. Personality psychology could be strengthened similarly by
integrating principles borrowed from evolutionary biology.

Human personality is often framed without consideration of its
evolutionary origins and consideration of the functionality of psy-
chological mechanisms generating individual differences in the
development, structure, and processes of personality. Throughout
the history of personality psychology, we have examined the
ll rights reserved.

lski).
1930/1949; Maslow, 1970; Murray, 1937; Murray, 1938), traits
(Allport, 1931; Allport, 1960), factors (Eysenck, 1981; John,
1990), drives (Freud, 1930/1949; Murray, 1938), motives (McClel-
land, 1961; Winter, 1973), and life tasks (Cantor, 1990) with little
or no recourse to questions central to an evolutionary perspective.
Importantly, however, evolutionary processes are as relevant to
humans as they are to other species. There is no reason to expect
that human nature or personality is exempt from natural or sexual
selective pressures.

Human personality is thus best conceptualized within the
framework of evolutionary psychology (see, Barkow et al., 1992;
Buss, 1991; Buss, 1990; Crawford, Krebs, & Smith, 1987; Daly &
Wilson, 1983). Evolutionary psychology suggests that the way we
think, feel, and behave today can be understood by considering
which thoughts, feelings, and behaviors increased the relative sur-
vival and reproduction of our ancestors. Manifesting certain
thoughts, feelings, and behaviors in certain contexts increased
ancestral humans’ abilities to out-survive and out-reproduce less
successful conspecifics. The offspring of these ancestors had some
probability of inheriting the genetic structure coding for the devel-
opment of the psychological mechanisms that in response to cer-
tain cues produce that same pattern of thoughts, feelings, and
behaviors. This process continued for the span of human evolution-
ary history such that patterns of thoughts, feelings, and behaviors
guided by the evolved psychological mechanisms are species-typ-
ical and encompass what we call human nature.

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510 R.L. Michalski, T.K. Shackelford / Personality and Individual Differences 48 (2010) 509–516
Any comprehensive theory of personality should provide an-
swers to the following questions: What is human nature? What
underlies individual differences in personality? Is personality
age-graded? Of the numerous variables on which humans differ
from one another, which criteria do we use to establish what con-
stitutes a personality trait? What supportive empirical evidence is
there for the theory? Does the theory generate specific testable
predictions, or is it based upon post hoc explanation of findings?
In what ways are the sexes predicted to be different? In what ways
are the sexes predicted to be similar? What causes these similari-
ties and differences? What follows is a presentation of a theoretical
framework of personality which aspires to answer each of these
questions.
2. Darwinian concepts and evolutionary products

The observation that species change over time was known long
before Darwin. Archaeological evidence had revealed changes in
morphology and had revealed structures of organisms that ap-
peared well-suited to the ecological niche occupied by members
of that species. What was lacking before Darwin was a causal
mechanism to explain how species change over time. The theory
of natural selection filled a gap in the explanatory framework
which allowed researchers to explain changes in species over time.
Darwin proposed natural selection as a solution to explain how
variation in morphological (including psychological) characteris-
tics better enabled organisms to survive and reproduce. The pro-
cess of natural selection requires three key components. Darwin
proposed that selection operates when (a) the characteristics of
individuals of a population vary, (b) this variation is heritable,
and (c) individuals reproduce differentially (Darwin, 1859; Mayr,
1982). Variation, selection, and differential reproduction are the
bases of natural selection. Among humans, for example, we vary
along a wide variety of dimensions. We vary in morphological
characteristics such as height and weight and we vary along psy-
chological dimensions such as sexual orientation, sexual desire,
and personality dimensions such as Dominance, Extraversion,
and Emotional Stability. There are also a variety of characteristics
along which humans do not vary. We do not currently vary, genetic
mutations excluded, along characteristics such as number of fin-
gers, the presence of belly buttons, and number of eyes. From Dar-
win’s perspective, it is only along those characteristics on which
we vary that natural selection can operate. Once variation on a par-
ticular trait or feature exists, natural selection operates on those
features best suited for survival and reproduction in the organism’s
current environment (whether physical, developmental, ecological,
social, etc.). The operation of natural selection requires that those
characteristics be heritable. Individuals lacking traits that in-
creased direct survival or reproduction or the survival or reproduc-
tion of kin would have been out-reproduced by those individuals in
ancestral environments who did have such traits. Through this pro-
cess, successful variants would have become more frequently rep-
resented among organisms of a species.

Darwin was puzzled, however, by the characteristics of organ-
isms that thwart survival and that are developmentally costly to
produce. Reconciliation of characteristics that impeded survival
through increased predation, for example, was accomplished by
Darwin with a second evolutionary theory—sexual selection theory
(Darwin, 1871).

Darwin’s (1871) theory of sexual selection was constructed to
explain traits that seemingly reduced an organism’s chances of sur-
vival. A human male’s greater aggression compared to human fe-
males comes at the cost of developing bodies capable of
engaging in such conflicts (e.g., larger size, greater caloric intake
necessary to grow and maintain such a body, maintaining higher
levels of testosterone which acts as an immunosuppressant). Dar-
win’s theory suggests that those features of organisms that in-
crease (a) the chances of being selected by the other sex as a
mate or (b) success in competition among members of the same
sex for sexual access to the other will be selected. These facts of
sexual selection are called intersexual selection and intrasexual
selection, respectively. For nearly a century after the publication
of sexual selection theory, focus was placed on biological sex as
the driving force behind sexual selection. Publication of Trivers’s
(1972) parental investment theory forced evolutionary scientists
to reformulate the impact of biological sex on sexual selection.
Trivers proposed that it is not biological sex that drives sexual
selection, but differences in the minimum obligatory parental
investment. Parental investment is defined by Trivers as any
investment that a parent makes in its offspring that increases that
offspring’s chances of survival at the expense of the parent’s ability
to invest in current or future offspring. This definition captures the
metabolic costs of investing in offspring and all other forms of
investment that benefit offspring.

Among humans, females make the larger obligatory investment
in their offspring (Clutton-Brock, 1991). Female sex cells are larger
and metabolically more costly to produce than are male sex cells.
Additionally, fertilization occurs internally within females. As a re-
sult, females incur the costs of gestation, parturition, and lactation.
A male’s minimum obligatory investment can end with the place-
ment of his sex cells in the reproductive tract of a female. Because
the costs associated with parental investment are not isomorphic
between the sexes, a suite of psychological characteristics are pro-
posed to exist in human females that are not expected to exist in
males. Following impregnation, a female’s reproductive opportuni-
ties are constrained by the investment that must be made during
pregnancy. A male’s reproductive opportunities are not con-
strained in similar fashion. A feature of this theory reveals that
there are trade-offs between mating effort and parenting effort
that are magnified in comparative research between species with
sexually-asymmetric parental investment. Among humans, for
example, a host of sex differences are expected to exist (Symons,
1979) that reflect investment differences that parents recurrently
made in their offspring. These sex differences are expected to have
arisen by processes of sexual selection that operated as a conse-
quence of the difference between the sexes in parental investment
in ancestral environments. Parental investment theory predicts
that human females will be the more discriminating sex. Research
has found consistently that females are less willing to engage in
sex, desire fewer sexual partners, require greater time to pass prior
to consenting to sex, have higher standards for sex partners, and
report being more upset over emotional aspects of a partner’s infi-
delity compared to sexual aspects of his infidelity (for a review see
Buss & Schmitt, 1993).

Cross-culturally, men invest substantially less than do women
in their offspring (Geary, 2000). Even in cultures with relatively
high paternal investment, maternal investment dwarfs paternal
investment. Parental investment theory generates expectations of
many sex-differentiated psychological mechanisms. The invest-
ment asymmetry between the sexes sets the stage for the evolu-
tion of mechanisms to solve social dilemmas posed by other
family members. Offspring, for example, would have been selected
to not allow the expression of genes that signaled dissimilarity to a
putative father. Fertilization, being internal to women, results in
paternity uncertainty for men. If men have psychological mecha-
nisms designed to detect dissimilarities (or similarities) between
themselves and their putative offspring, then selection would
operate on offspring to produce phenotypic anonymity.

Future research is necessary to understand the developmental
trajectories of specific psychological mechanisms designed in re-
sponse to the selection pressures hypothesized by parental invest-

R.L. Michalski, T.K. Shackelford / Personality and Individual Differences 48 (2010) 509–516 511
ment theory. One avenue of sex-differentiated psychology await-
ing further empirical scrutiny is the impact of early family experi-
ences on later mating strategies. Research on attachment styles
and mating strategies reveals that female mating strategies may
be calibrated to anticipate certain mating environments later in life
based on the availability of parents and expectations that others
will invest earlier in life. This relationship does not hold as strongly
for males. Future research is necessary to examine why some fea-
tures of sexual psychology and behavior related to early childhood
experiences are present for females (Belsky, Steinberg, & Draper,
1991) and others emerge only for males (Michalski & Shackelford,
2002). Michalski and Shackelford, for example, found that men’s
desired sexual strategies later in life are related to their birth .
Similar relationships do not hold for women. Why might men’s
mating strategy be calibrated by their birth and women’s
mating strategy be calibrated by the attachment they develop with
their parents? To answer these questions it is necessary to under-
stand the products of evolutionary processes.

The filtering processes of natural and sexual selection result in
three products: adaptations, by-products of adaptations, and ran-
dom variation or noise. Adaptations are the primary products of
natural and sexual selection and can be defined as a ‘‘reliably
developing structure in the organism, which, because it meshes
with the recurrent structure of the world, causes the solution to
an adaptive problem” (Tooby & Cosmides, 1992, p. 104). Adaptive
problems refer to recurrent features of ancestral environments that
impeded successful survival or reproduction. Buss (2007) presents
the example of a preference for sweet, calorically dense foods. In
ancestral environments, when access to food was less reliable than
it is today, selection favored adaptations in humans that func-
tioned to increase immediate caloric content. The criteria utilized
to identify adaptations are stringent (Williams, 1966); adaptations
must show features of special design, including efficiency, preci-
sion, and reliability.

Some products of evolution, however, were not directly se-
lected. By-products of adaptations include features or effects that
are not considered to be adaptations but that tag along with an
adaptation. In this sense, and as has been debated among evolu-
tionary psychologists, rape may be an example of one such by-
product (Thornhill & Palmer, 2000). Men, more often than women,
are perpetrators of rape. Men, more than women, report a greater
desire for sexual variety and for short-term sexual intercourse and
a greater propensity to use physical violence to secure many differ-
ent types of resources. Rape therefore might represent a phenom-
enon that is a by-product of adaptations that performed other
functions for ancestral men (e.g., increased reproductive success
from pursuit of a short-term mating strategy and greater resource
acquisition and reputational advantages through the use of physi-
cal aggression).

Random variation or noise refers to those characteristics that are
selectively neutral or ‘‘overlooked” by natural and sexual selection
but that are produced through random mutation or developmental
anomalies. In the design of certain physical characteristics, for
example, the shape of one’s belly-button serves no adaptive func-
tion but is a characteristic along which people do vary.
3. Applications of evolutionary psychology to personality
psychology

The marriage between concepts developed within evolutionary
psychology and within personality psychology has a brief history.
The historical divide between these two areas lies in the historical
focus of each area. Evolutionary psychological accounts of human
nature have focused largely on species-typical and sex-typical char-
acteristics that have evolved in response to the problems of survival
and reproduction faced by our ancestors. Personality psychology, in
contrast, has been concerned largely with the ways in which hu-
mans differ. The divide between these two fields is obvious and
raises questions that evolutionary psychologists need to address.
If natural and sexual selection operates to filter less successful vari-
ants, why are stable, heritable individual differences maintained?
The first theoretical link between these two literatures and attempt
to reconcile this issue was provided by Buss (1984), who outlined
four criteria according to which important sources of evolutionarily
informed individual differences can be identified. These include
heritability, inclusive fitness, sexual selection, and assortative mat-
ing. Each of these four criteria can be used to bridge the theoretical
gap between evolutionary psychology and personality psychology.

Buss (1991) and Buss and Greiling (1999) propose that person-
ality may not reflect evolutionary noise or represent by-products of
other adaptations but may instead reflect the social landscape of
adaptive strategies. Buss highlights that there are at least four
explanations for personality and individual differences in humans

1) Differences in personality are heritable alternative
strategies.

2) Differences in personality are calibrations to fluctuating
strategies throughout development.

3) Differences in personality are due to contextual differences
and personality reflects those contexts.

4) Personality differences emerge through calibration to vari-
ous thresholds in development.

Appreciating that personality differences between individuals
may reflect social landscapes, it is reasonable to question whether
personality has an impact on shaping sexual desire, motivation,
and attraction. Personality can be used as a source of information
that answers some of the most important social dilemmas that hu-
mans have evolved to solve. Evolutionary psychologists have ar-
gued, for example, that the Big-Five personality characteristics
summarize the most important facets of social landscapes. Perceiv-
ing, attending to, and acting upon differences in others likely
would have yielded important benefits in ancestral environments.
For example, Conscientiousness may be evaluated to assess whom
to trust to complete important tasks. Agreeableness may be evalu-
ated as an index of an individual’s willingness to cooperate and to
conform to group norms by suspending their individual concerns.
Openness/Intellect of others can be used as a criterion for seeking
out advice. Neuroticism may signify the inability to negotiate tasks
effectively. Extraversion or surgency may be assessed as an index
of who is likely to rise in the local status hierarchy.

From an evolutionary psychological perspective, human person-
ality structure is comprised of a finite though numerous collection
of species-typical, relatively domain-specific psychological mecha-
nisms that have evolved over human evolutionary history because
they solved the adaptive problems ancestral humans confronted.
Personality is the output of psychological mechanisms. Every theory
of human personality—even the most environmentalistic—assumes
that personality is at some basic level constructed of psychological
mechanisms (Symons, 1987). If two members of a given species, or
if two members of two different species are exposed to identical
stimuli and respond in non-identical ways, we must infer the exis-
tence and operation of mechanisms internal to the organisms.
These mechanisms can best be described as information-processing
devices. These mechanisms take in certain classes of information,
process that information according to a set of decision rules, and
then generate output correlated with survival or reproductive suc-
cess in ancestral environments. The information accepted for pro-
cessing into the mechanism may come from other psychological
mechanisms internal to the organism, or it may originate in the
external environment—more often than not the particularly social

512 R.L. Michalski, T.K. Shackelford / Personality and Individual Differences 48 (2010) 509–516
environment comprised of other humans operating according to
like mechanisms. The output generated by a psychological mecha-
nism may be in the form of information which is channeled to and
accepted by other psychological mechanisms internal to the organ-
ism. The output alternatively may be in the form of behavior, affect,
or cognition enacted by the organism (Buss, 1991).

The psychological mechanisms underlying personality have
evolved over human evolutionary history because they solved the
adaptive problems ancestral humans confronted. Certain problems
have been recurrently faced by ancestral humans. Consider the
problem of which foods to ingest. To survive, certain nutrients
had to be ingested and, conversely, various toxins had to be
avoided. This is a complicated problem when considered at the le-
vel of basic decision processes. Ancestral humans had to distin-
guish nutritive from non-nutritive goods, poisonous from non-
poisonous fruits, vegetables, and organisms, calorically dense foods
from less calorically dense foods, and so on. Those proto-humans
who could not distinguish nutritive from non-nutritive foods are
not our evolutionary ancestors, for they were out-reproduced by
their more discriminating conspecifics.

Personality is comprised of a finite though numerous collection
of evolved psychological mechanisms. The adaptive problems our
ancestors faced were many and varied in nature: from mate selec-
tion, to food ingestion, to forming successful reciprocal dyadic alli-
ances (friendships). The solution to each of these problems has
evolved as a circumscribed set of decision rules that guide human
behavior, thought, and affect (in concert with relevant cues). The
fact that one might be successful in selecting a reproductively valu-
able mate has little or no bearing on whether one can successfully
select and ingest the most nutritive foods available. Mate selection
and food selection are qualitatively different adaptive problems
that will have selected for qualitatively different sets of psycholog-
ical mechanisms over human evolutionary history. Thus, the psy-
chological mechanisms that comprise human personality
structure will be as numerous as the adaptive problems that se-
lected for those mechanisms. Relatedly, because the number of
adaptive problems that ancestral humans confronted was finite
though numerous, we expect that the number of mechanisms com-
prising the structure of personality are finite though numerous.
Moreover, it follows that these finite though numerous mecha-
nisms are domain-specific—that is, they serve as evolved solutions
to specific adaptive problems. Because ancestral humans did not
confront a single ‘‘survive and reproduce” adaptive problem, we
have no reason to expect that personality is comprised of a single
‘‘survive and reproduce successfully” psychological mechanism
that evolved as a relatively domain-general adaptive solution
(Buss, 1991; Symons, 1987; Tooby & Cosmides, 1990; Tooby &
Cosmides, 1992). Over the history of research on evolutionary the-
ories of psychological phenomena, confusion has surrounded and
continues to surround whether invoking concepts such as do-
main-specific evolved psychological mechanisms implies reflexive
triggering of that particular mechanism (Barrett & Kurzban, 2006).

Finally, the basic structure of human personality is comprised of
a species-typical collection of evolved psychological mechanisms.
That is, the mechanisms that evolved as solutions to the adaptive
problems confronting all ancestral humans over evolutionary his-
tory are presently characteristic of all representatives of the human
species (with the exception of mutations and genetic drift). This is
expected because all modern humans are, by definition, the evolu-
tionary descendents of those ancestral humans who successfully
solved the various adaptive problems they confronted. If it is the
case, then, that personality is comprised of a finite though numer-
ous species-typical and domain-specific psychological mecha-
nisms, does this mean that personality is stable or consistent
throughout the lifespan? Or might it be somehow dependent on
the context or environment?
Evolutionary psychological theories do not imply the existence
of adaptations that are incapable of change or are forever bound
by our genome (Bjorklund & Pellegrini, 2002; Buss, 2003; Tooby
& Cosmides, 1992). The environment is integral in shaping the
expression of evolved modules of the mind. Examinations of the
arguments surrounding the claims that evolutionary psychology
is a theory of genetic determinism must start with an examination
of what evolutionary psychologists actually propose. Tooby and
Cosmides (1992) argue that developmental programs responsible
for assembling an adaptation are also adaptations whose primary
function is to reconstruct in offspring the design that enhanced
reproduction in the preceding generation. They specifically note
that it is useful to consider genes together with developmental pro-
grams as an integrated suite of adaptations. The reliable develop-
ment of an organism’s phenotypic features (including
personality) does not imply that these features are not modifiable.
Developmental programs do not assemble an organism of fixed de-
sign but rather a set of expressed adaptations according to vari-
ables such as age, sex, and circumstance-dependent design
specifications. Adaptive problems are often specific to particular
life stages. Organisms benefit from the necessary adaptations for
their particular age regardless of whether they appear before they
are necessary or continue after they are necessary. Tooby and Cos-
mides argue that every feature of every phenotype is equally deter-
mined by the interaction of that organism’s genes and its
ontogenetic environment. Biology, therefore, cannot be applicable
to some but not all traits. In stressing the role of the environment,
Tooby and Cosmides note that the ‘‘developmentally relevant envi-
ronment” refers to those features of the world that are rendered
developmentally relevant by the evolved design of an organism’s
developmental adaptations. The assumption that genes are, there-
fore, the only target of natural selection is a misconception. Genes
and developmentally relevant environments (species-typical envi-
ronments) are both products of the evolutionary process. By sifting
between alternative developmental programs, for example, the
evolutionary process also is selecting the triggers that the mecha-
nisms will use to build an adaptation. Regarding the expected
age-graded structure of human personality, different adaptive
problems confronted ancestral humans at different ages or devel-
opmental stages, as is true of modern humans. Thus, for example,
an adaptive problem of late infancy or early childhood, but presum-
ably not of older individuals selected for mechanisms that come
online at or around the time in which these adaptive problems
were likely to have been confronted in ancestral environments.

Evolution by natural and sexual selection is recognized as the
origin of the many special-purpose and domain-specific cognitive
decision rules (psychological mechanisms) according to which hu-
mans function. However, and crucial to this perspective, evolution-
ary psychology holds as a central goal to determine the historical,
developmental, and situational forms of contextual input pro-
cessed by the psychological mechanisms that guide human behav-
ior. Evolutionary psychologists are not genetic determinists. Rather, a
key message of evolutionary psychology is that the complex …