EASY! one to two slides David Buss's evolutionary theory of personality

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

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

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

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

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 Solutions (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

• 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

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.

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

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 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 Solutions (Mechanisms)

Problem Solution/Mechanism

Survival

Taking in information from the external world Eyes, ears, nose, skin, & tongue

Temperature regulation Ectothermic system, sweat glands

Disease and parasites Immune system

Wounds and injury Blood clotting

Predators and danger Limbs and locomotion

Fending off attacks of enemy Strength, aggression, speed

Trust/Cooperation Conscientiousness, agreeableness

Alliance and group cohesion Dominance, agreeableness

Food gathering Creativity, intelligence

Shelter Creativity, intelligence

Reproduction

Mate attraction Dominance, surgency, creativity

Mate selection Social intelligence, theory of mind

Trust Conscientiousness, dependability

Intrasex competition Aggression, drive, achievement,

resource acquisition, beauty

Intimacy Love, attachment, agreeableness

Adapted from Buss, 1991 & MacDonald, 1995 .

428 Part V Biological/Evolutionary Theories

We will not say much about goals, drives, and emotions and instead will focus

mostly on personality traits as evolved mechanisms. We will see, however, that

goals, motives, and emotions are closely connected to personality. In fact, most

theories of personality have centered around motivation and drive.

Motivation and Emotion as Evolved Mechanisms

Two goals and motives that act as evolved mechanisms are power and intimacy. These

drives take many different forms, with power taking the form of aggression, dominance,

achievement, status, “negotiation of hierarchy,” and intimacy taking the form of love,

attachment, “reciprocal alliance.” Evolutionary psychology refers to these drives as

“adaptations” because they directly affect the health and well-being of the person.

Similarly, emotions are adaptations because they directly alert the individual

to situations that are either harmful or benefi cial to his or her well-being (Lazarus,

1991). If an event is harmful to a person’s well-being, some form of negative

emotion is experienced. Likewise, if an event occurs that is benefi cial to that person’s

well-being, some kind of positive emotion occurs. For example, if the harm

is in the form of loss, then sadness is experienced, whereas if the harm is in the

form of insult then anger is experienced. Similarly, pride is experienced when one

perceives the event as important and successfully carried out.

Motivation and emotion are directly linked with stable personality traits

(Buss, 1991; cf. MacDonald, 1995). If one regularly is driven to achieve and win

in competitions and is status-oriented, then we label that person as “dominant” or

“power-oriented.” A person who regularly acts in ways to bring people together is

“agreeable.” Likewise, if one often experiences sadness, shame, guilt, or anxiety

when other people do not, we might say that person is “anxious.” Motivation is

part of personality.

Personality Traits as Evolved Mechanisms

Buss (1991) starts with the assumption that motivation, emotion, and personality

are adaptive in that they solve problems of survival and reproduction. He

argues that the fi ve main dimensions of personality (Big Five) can be best

thought of as a way of summarizing the social landscape; that is, they signal to

other people our ability to solve survival and reproductive problems. Buss conceptualizes

individual differences and personality as strategies for solving adaptive

problems. More importantly, being sensitive to and aware of these differences

in personality affords reproductive advantages in the perceiver. If you

know who is cooperative and/or dominant, you have an advantage over those

who are oblivious to such traits. “Whenever individuals differ in ways relevant

to the problems of survival and reproduction that humans must solve, a selective

advantage would accrue to those whose capacity to discern the differences

enabled them to increase their inclusive fi tness” (p. 473). Put differently, these

dispositions are inherently evaluative, that is, they allow others to evaluate us

on the adaptive problems; dispositions signal to other people their ability to

solve survival and reproductive problems. For example, conscientiousness signals

whom to trust with tasks, and those who do this well accrue a selective

advantage (i.e., are more attractive to others).

Chapter 15 Buss: Evolutionary Theory of Personality 429

Buss’s model of personality very closely resembles the Big Five trait approach

of McCrae and Costa but it is not identical in structure. Buss argues for essentially

the same fi ve personality dimensions but with slightly different terminology. Moreover,

his view is that these behavioral dispositions have adaptive signifi cance:

• Surgency/extraversion/dominance

• Agreeableness

• Conscientiousness

• Emotional stability (opposite of neuroticism)

• Openness/intellect

Surgency involves the disposition to experience positive emotional states

and to engage in one’s environment and to be sociable and self-confi dent. A

surgent person is one who is driven to achieve and often tends to dominate and

lead others. It is nearly synonymous with “extraversion.” In ancestral times,

these individuals were high in status and were therefore attractive and desirable

mates. Put into the language of evolution, surgency involves “hierarchy proclivities”;

that is, how people negotiate and decide who is dominant and who

is submissive. The negotiations happen, as they do in many animals, through

competition and power struggles. In ancestral times these competitions were

more often than not physical and aggressive, but could also be verbal and

through accumulation of wealth and resources. Leaders are those who take

charge and direct others, and whether they take charge by force or by persuasion

they are acknowledged by others to be in charge and are in a dominant

social position. Because power and dominance are attractive, these individuals

also tended to have more children. Surgency is also marked by a tendency to

take risks and to experience positive emotion (i.e., be happy) and initiating and

maintaining friendships and relationships. People high in surgency are also

driven and ambitious.

A second dimension of personality, agreeableness/hostility , is marked by a

person’s willingness and capacity to cooperate and help the group on the one hand

or to be hostile and aggressive on the other. Some people are warm, cooperative,

and group-oriented, but others are more selfi sh and hostile toward others. Agreeable

individuals are likely to work to smooth over group confl ict and form alliances

between people. Agreeable people foster group cohesion and tend to conform to

group norms. They get along and go along with others. In short, agreeableness

marks a person’s willingness to cooperate.

The third adaptive personality system revolves around response to danger

and threat. All animals have alarm systems that warn them of potential danger and

harm. In humans and other animals this takes the form of anxiety as an emotional

state and emotional stability/neuroticism as a dispositional trait. Vigilance or

sensitivity to harm and threat is quite necessary and adaptive. Emotional stability

involves one’s ability to handle stress or not. Some people are calm under stress

while others are high-strung much of the time.

Fear and anxiety are adaptive emotions. Without them we would certainly

die as individuals and as a species. As we discussed in the McCrae and Costa and

the Eysenck chapters, neuroticism is the tendency to experience negative emotion

such as anxiety, guilt, and sadness. The tendency to be sensitive to threats, for

430 Part V Biological/Evolutionary Theories

instance, may well have been adaptive in dangerous environments like those in

which our ancestors lived. Heightened anxiety would provide a signal of danger

and threat; its absence would quickly lead to extinction of the species. Consider

a hunter on the savannah. He hears the growl of a large animal and becomes

fearful. He drops back behind the bushes before the animal becomes aware of his

presence. If he did not feel anxious, he might not hide, with dire consequences

for his safety. By the same token, the other extreme—hypersensitivity to threats—

would be debilitating and disruptive to everyday functioning. If the same man

who became fearful at hearing the growl of a large animal also became fearful

with every rustling of leaves or every sound of the wind, he would have a hard

time functioning in everyday life. Having some degree of fearfulness is adaptive,

and people with that quality were more likely to survive, reproduce, and pass on

that disposition. Naturally selected traits are favored if they increase one’s chances

of survival and reproductive success.

Fourth, one’s capacity and commitment to work is the core characteristic of

conscientiousness. Conscientious people are careful and detail-oriented as well as

focused and reliable. Less conscientious people are less reliable and dependable

and tend to lack focus. Conscientiousness signals to others whom we can trust with

tasks and responsibilities and whom we can depend on in times of need.

Finally, the evolved strategy of openness involves one’s propensity for innovation

and ability to solve problems. It is closely aligned with intellect and intelligence

but also a willingness to try new things and a willingness to have novel

experiences rather than sticking with one’s routine. These people are the explorers

of a group—they forge ahead where others are hesitant. In ancestral times this

quality might be expressed in willingness to explore new territories for food or

vegetation, but today it might be expressed in artists and scientists who are at the

cutting edges of ideas and knowledge.

Buss (1991) argues that of the fi ve personality dimensions, surgency/dominance,

agreeableness, and conscientious are the most important traits because they most

directly provide answers to a host of adaptive problems. For example:

• Who is high or low in the social hierarchy?

• Who possesses the resources that I need?

• With whom should I mate?

• Who might harm me or betray my trust?

• Who will make a good member of my group?

• Whom can I trust and depend on when in need?

Personality differences function to solve adaptive problems by providing answers

to these questions for both the individual and for others. In this sense they are

indicators of fi tness, much like the peacock’s plumage.

Origins of Individual Differences

As we discussed earlier, evolutionary theory is inherently a nature and nurture

perspective when it comes to origins. Buss and his colleague Heidi Greiling propose

four distinct sources of individual differences (D. Buss & Greiling, 1999). In

essence, these sources of difference come down to nature (biological-genetic) and

Chapter 15 Buss: Evolutionary Theory of Personality 431

nurture (environmental-social). An overview of the four major sources of individual

differences is presented in Table 15.2.

Environmental Sources

There are numerous ways in which the environment contributes to adaptive individual

differences. Adaptive differences increase reproductive success and one’s

chance of survival. One environmental source of personality differences is what

Buss termed early experiential calibration , by which he meant that childhood experiences

make some behavioral strategies more likely than others. An example of

such calibration is if people grow up without a father present, they are more likely

to be sexually active at a young age and have more sex partners during adolescence

and adulthood. People in this situation cultivate a more promiscuous sexual strategy

because parental attention is not reliable and adult relationships are viewed as

transient (Belsky, Steinberg, & Draper, 1991).

Another example of early calibration of adaptive strategies is attachment

style, as we fi rst discussed in the Klein chapter (5). Attachment between caregiver

and infant is inherently adaptive—without such an attachment the baby

does not survive the fi rst few weeks of life (Buss & Greiling, 1999). Adult

attachment increases support, protection, and reassurance, and if attachment is

the model the child experiences, then he or she is likely to develop similar

relationships in adulthood. Similarly, avoidant attachment signals parental

unwillingness to invest in the child.

A second origin of environment induced individual differences is alternative

niche specialization, which means that different people fi nd what makes

T A B L E 1 5 . 2

Origins of Individual Differences (Buss & Greiling, 1999)

Environmental Sources of Adaptive Individual Differences

1. Early environmental calibration

2. Enduring situational evocation

3. Strategic niche specialization

Heritable (Genetic) Sources of Adaptive Individual Differences

1. Adaptive self-assessment of heritable attributes

2. Frequency-dependent adaptive strategies

3. Continuous condition-dependent heritable strategies

Nonadaptive Sources of Individual Differences

1. Neutral genetic variation

2. Incidental by-products of adaptive variation

Maladaptive Sources of Individual Differences

1. Genetic defects

2. Environmental insults/trauma

432 Part V Biological/Evolutionary Theories

them stand out from others in order to gain attention from parents or potential

mates. One example of niche specialization is seen in birth order, as we saw

in the Adler chapter (3). Children of different birth orders gravitate toward

different personalities, interests, and activities because that is the only way to

gain attention from their parents. Frank Sulloway (1996) argued that fi rst born

fi nd their “niche” by identifying with parents and authority fi gures, whereas

second and latter borns fi nd their “niche” by being focused on overthrowing

those in power (i.e., older siblings).

Heritable/Genetic Sources

As we saw in the Eysenck and McCrae and Costa chapters, heritability is the extent

to which a trait is under genetic infl uence. Body type, facial morphology, and

degree of physical attractiveness act as heritable sources of individual differences

(Buss & Greiling, 1999). That is, muscular men or men with masculine, dominant

looks will garner more female attention, which will lead to more opportunities for

sexual activity, than will thin men or men with less dominant looks (Mazur,

Halpern, & Udry, 1994). These are heritable because the shape of one’s face or

body is mostly controlled by genetics.

Nonadaptive Sources

Some sources of individuals do not benefi t survival or reproductive success and

hence are categorized as “nonadaptive.” The most common nonadaptive source of

individual differences is neutral genetic variations , which most often take the form

of genetic mutations. Some mutations are neutral in that they are neither harmful

nor benefi cial to the individual. They may stay in the gene pool indefi nitely until

pressures of natural or sexual selection eliminate them.

Maladaptive Sources

Maladaptive traits are those that actively harm one’s chance for survival or decrease

one’s sexual attractiveness. These can stem from either genetic or environmental

sources. One genetic source is genetic defect , but in this case the mutation is harmful

to the person. An environmental source is seen in environmental trauma , such as

brain or spinal cord injury, which can also lead to maladaptive individual differences.

Neo-Bussian Evolutionary Theories of Personality

David Buss was the fi rst to formally propose a complete evolutionary theory of

personality, but others have followed and made advances to the theory. MacDonald

(1995), for example, furthered Buss’s theory with two main contributions. First,

he tied personality more closely to evolved motivational and emotional systems,

and second he argued that the range of personality variation we see on the main

dimensions of personality are viable alternative strategies for maximizing fi tness.

MacDonald, similar to Buss, also tied personality dimensions to evolved

strategies for solving adaptive problems. These behavioral strategies are

Chapter 15 Buss: Evolutionary Theory of Personality 433

connected either with motivation to approach or avoid situations or with the

emotional system of negative or positive affect. MacDonald however, only

had four personality dimensions (dominance, conscientiousness, nurturance,

and neuroticism) and left out openness.

MacDonald further argued that it is adaptive for a species to produce

individuals that vary along a continuum in their responses to important problems

because changing environments require different responses. That is what

MacDonald means by “viable alternative strategies for maximizing fi tness.” For

instance, in relatively safe environments, anxiety and vigilance are not as adaptive

as they are in relatively dangerous environments. Animals can afford to be

bold in safer environments. Some environments may favor risk takers and other

environments may favor risk avoiders. Indeed, in non-human animals we see

just such adaptive changes to changing environments (Nettle, 2006). For example,

in Guppie fi sh populations with relatively few predators, boldness is a common

trait, but if predators are introduced, this trait becomes less common in

just a few generations (cf. O’Steen et al., 2002). Note too, these traits are heritable

and have a genetic basis, which is one criterion for an adaptation.

Similarly, Nettle (2006) recently expanded on evolutionary theories of

personality and argued that Tooby and Cosmides’s (1990) argument that personality

could not be an adaptation failed to appreciate how environmental

change and variability would ultimately select for individual differences in

behavior within a given species. Nettle (2006) reviewed numerous studies from

the non-human animal literature that report how sudden changes in the environment

(just a few generations), increased the proportion of animals that had

traits adaptive to that environment. When the environment switched back to

the original conditions, animals on the other end of that dimension became

more common again. For example, some female chickadees are bold and

exploratory, whereas others are inhibited. In food-poor years, the more exploratory

birds are most likely to survive (Dingemanse, Both, Drent, & Tinbergen,

2004). In food-rich years, however, the bolder and more exploratory female

birds are less likely to survive, possibly because they are more likely to become

involved in dangerous encounters with predators. In short, evolution favors

individual differences because one can never predict what the future holds and

which qualities will best match changes in the environment.

Furthermore, Nettle (2006) hypothesized there have been fi tness costs and

benefi ts of each of the Big Five dimensions of personality during ancestral

periods of evolution (see Table 15.3). For example, benefi ts of being extraverted

include being more successful at mating, making social allies, and

exploring one’s environment, whereas evolutionary costs of extraversion

include taking more physical risks and having potentially a less stable family

(i.e., more affairs). A benefi t of being open to experience is heightened creativity,

and its costs are having more unusual beliefs and possibly even developing

psychosis. High levels of conscientiousness have the benefi t of causing one to

pay closer attention to the details of physical self-care and hence can lead to

a longer and healthier life, but also heighten the risk of leading to rigid and

compulsive behavior.

434 Part V Biological/Evolutionary Theories

Common Misunderstandings in

Evolutionary Theory

When evolutionary theory fi rst became popular in the 1980s it caused quite a bit

of controversy. There was a lot of resistance both from inside and outside university

settings against applying evolutionary ideas to human thought and behavior.

Although much of this resistance has died down over the last 20–30 years, there

are some misunderstandings that still occur (D. Buss, 1999).

Evolution Implies Genetic Determinism (Behavior as Set

in Stone and Void of Infl uence From the Environment)

Evolution is all about the body changing due to changes in the environment. In this

sense it is inherently a “nature and nurture” interaction perspective. Evolution occurs

from the interaction between adaptations and input from the environment that triggers

the adaptations. Buss uses calluses as an example: Calluses are evolved adaptations

but do not get expressed without input from the environment such as walking barefoot

for long periods of time or playing the guitar. Calluses get expressed through genetically

induced protein formation and this gene expression only occurs with input from

the environment (Ulrich-Vinther, Schwarz, Pedersen, Soballe, & Andreassen, 2005).

More generally, the discovery of epigenetics is an even more powerful example

of how genetic infl uence is not set in stone at the moment of conception and

interacts with input from the environment. Epigenetics is change in gene function

that does not involve changes in DNA (Meaney, 2010; Rutter, 2006). In other

T A B L E 1 5 . 3

Costs and Benefi ts of Big Five Dimensions of Personality (Nettle, 2006)

Domain Benefi ts Costs

Extraversion Mating success; social allies; Physical risks; family stability

exploration of environment

Neuroticism Vigilance to dangers; striving and Stress and depression, with

competitiveness interpersonal and health

consequences

Openness Creativity, with effect on Unusual beliefs; psychosis

attractiveness

Conscientiousness Attention to long-term fi tness Missing of immediate fi tness

benefi ts; life-expectancy and gains; obsessionality; rigidity

desirable social qualities

Agreeableness Attention to mental states of Subject to social cheating;

others; harmonious interpersonal failure to maximize selfi sh

relationships; valued coalitional advantage

partner

From Nettle (2006), copyright American Psychological Association; reprinted with permission.

Chapter 15 Buss: Evolutionary Theory of Personality 435

words, experiences that animals have create tags that attach to the outside structure

of DNA and control gene expression. Epigenetics has fundamentally altered our

view of genetic infl uence. It makes clear that the experiences we have (such as

eating, drinking, or being exposed to chemicals) can affect changes in genes

(Watters, 2006). In fact, cancers are one of the most widespread examples of epigenetic

change in gene expression and demonstrate tragically how what we eat,

drink, and smoke can alter genetic activity (Jones & Baylin, 2002). In fact, in a

very real sense, changes in organs, physiological systems and bodies that occur

over long periods of time (i.e., evolution) are the result not only of mutations in

genes but also epigenetic processes. In short, that DNA is not destiny is perfectly

consistent with evolutionary theory.

Executing Adaptations Requires Conscious Mechanisms

To say that mechanisms (cognitive and personality) evolved to solve important

problems of survival and reproduction does not mean they require complex (conscious)

mathematical abilities to operate. For example, the idea of “inclusive fi tness”

revolves around the idea that we are more likely to help out a brother than a cousin and

a cousin more than a stranger because the brother is more closely related to us

and a cousin is more closely related than a stranger. This is not a mathematical

calculation any more than a spider needs to understand geometry to spin a web.

Moreover, when evolutionary psychologists talk about “strategies,” these are not to

be thought of as conscious or willful acts. In fact, people have no awareness of

these infl uences and when discussed often even regret them. “Ugh, I am not attracted

to him because of his resources and fi tness!” “Sexual strategy” is just a short-hand

term for a cumbersome idea that evolution has shaped our preferences for mates

based on the fact that we are attracted to those who produce healthy and fi t offspring

and ideally continue to provide for them. This increases the likelihood that they will

survive to reproductive age and pass on their healthy genes.

Mechanisms are Optimally Designed

People sometimes draw the conclusion that evolution produces solutions that are

optimal. In fact, some adaptations are rather awkward. Evolutionary change occurs

over hundreds of generations and there is always a lag between adaptation and

environment. Human preference for fatty and salty foods is a good example. In

ancestral environments tens of thousands of years ago, fatty and sugary foods were

very diffi cult to obtain. Yet they provide important nutritional benefi ts. Over the

last 100 years, fat and sugar have become cheap and plentiful. Our waistlines have

bulged to the point where two-thirds of adult Americans are now either overweight

or obese (Flegal et al., 2010). If they were optimally designed they would be more

effi cient and respond more quickly to changes in the environment.

Related Research

The evolutionary model of personality cannot be tested directly insofar as we cannot

conduct studies over hundreds of generations. And yet, just like in biology,

there is much support for the evolutionary basis of human personality, which can

436 Part V Biological/Evolutionary Theories

be divided into at least three general topics: temperament, genetics, and animal

personality. All three lines of evidence support the view that personality has a

biological basis and that these biological systems have evolved.

Temperament and the Pre- and Post-Natal Environment

Most every parent of two or more children knows that babies are different from

one another from their very fi rst day. These differences in behavior have a biological

basis and are known as temperament (A. Buss, 2012). Temperament lays

the foundation for later personality traits. Insofar as temperament is expressed

before and immediately after birth means it develops mostly from biological systems,

but is modifi ed by input from the environment. Moreover, differences in

these biological systems between individuals—some are more active and others are

more sensitive to sensory stimulation—have been shaped by natural and sexual

selection pressures, that is, by evolution.

Evidence suggests that temperament and personality differences are manifest

even before birth, prenatally. Apparently, fetal activity and heart rate can reveal something

about temperament differences over the fi rst year of life (DiPietro et al., 1996).

In particular, a high heart rate at 36 weeks’ gestation (nearly full term) foreshadowed

less predictable eating and sleeping habits 3 and 6 months after birth and less emotionality

at 6 months after birth. Having high activity levels at 36 weeks’ gestation

predicted being slow to adapt to new people or situations and having more irregular

eating and sleeping habits at 3 and 6 months as well as being more diffi cult or fussy

at 6 months (DiPietro et al., 1996).

The prenatal environment plays an important role in shaping personality. In

fact, the amount of stress the mother experiences during pregnancy may alter the

infant’s own stress response. That is, infants born to mothers who have experienced

an unusual amount of stress during pregnancy tend to have impaired stress function;

higher baseline levels of stress hormones; and a faster, stronger, and more

pronounced physiological response to stress, all of which persist into childhood

(Barbazanges et al., 1996; Clark & Schneider, 1997).

After birth, in the immediate post-natal period, newborn infants already

display regular and consistent differences in behavior; that is, they have distinct

temperaments (A. Buss, 2012). These behavioral differences are most pronounced

in four dimensions of temperament: activity, emotionality, sociability, and impulsivity.

Activity is simply how active the baby is and how much energy he or she

uses in doing things, that is, how quickly or slowly the newborn does things.

Emotionality is seen in how frequently and intensely the baby experiences either

positive or negative emotion, that is, how happy or fussy the baby is. Sociability

concerns the baby’s response to other people, especially strangers. Some babies

are sociable and outgoing and others withdraw and cry or are reserved and shy

in the presence of strangers (Clarke-Stewart, Umeh, Snow, & Peterson, 1980).

Finally, impulsivity involves the readiness and speed to act, without refl ection. All

infants are relatively impulsive but even in infancy there are consistent differences

between babies. These differences tend to become more noticeable during childhood

and adolescence. Moreover, long-term research has reported that toddlers

who have impulsive temperaments are more likely than other toddlers to commit

Chapter 15 Buss: Evolutionary Theory of Personality 437

criminal activity and have diffi culty with alcohol by the time they reach age 21

and also perform worse academically and have lower SAT scores (Caspi, 2000;

Mischel, Shoda, & Rodriguez, 1989).

Genetics and Personality

Partly due to how genetics was taught in high-school biology, a common assumption

many people have is that there is a simple and nearly one-to-one correspondence

between genes and traits. Recall how you learned to calculate the probability that

offspring would inherit a trait if its parents were either dominant or recessive carriers

of that trait. There are simple categorical traits (e.g., eye color) that get

transmitted by one gene. But all complex psychological traits that are expressed

on a continuum from low to high get transmitted by many, many genes. More

technically, simple categorical traits are “monogenically” (single gene) transmitted,

whereas traits that range from a little to a lot (e.g., aggression, height, weight,

anxiety) are “polygenically transmitted” (Ebstein, 2006; Evans et al., 2007). Simply

put, monogenic transmission happens when single genes produce single traits

(phenotypes), and polygenic transmission occurs when many genes interact to

create a single characteristic (Rutter, 2006). This distinction is very important in

understanding a fundamental idea in modern genetics, namely our genome is the

starting point, not the end point, for how our genes are expressed (our phenotype).

There is no “smart” gene, “shy” gene, or “aggressive” gene. Many, many (dozens

and maybe more) genes are responsible for personality traits.

When studying behavioral genetics, researchers use two major methods to

examine the relationship among genetics, behavior, and personality. With the fi rst

method, the quantitative trait loci (QTL) approach, they look for the location of

specifi c bits of DNA on genes that might be associated with particular behaviors. In

this sense, it is a search for “genetic markers” of behavior. The traits are quantitative

because they are markers for behaviors that are expressed on a broad continuum,

from very little to very much. For example, anxiety is a quantitative trait because

some people are not at all anxious, most people are average, and a few are very

anxious. The QTL method uncovers the location on particular genes that is associated

with high or low levels of a trait. These locations are also known as “markers.”

QTL research points to genetic markers for several basic personality traits,

such as novelty- or thrill seeking, impulsivity, and neuroticism/anxiety (Benjamin

et al., 1996; Hamer & Copeland, 1998; Lesch et al., 1996; Plomin & Caspi, 1999;

Retz et al., 2010; Rutter, 2006). Consider the case of thrill seeking, a trait that entails

risk taking. People with this trait may seek out highly exciting activities like bungee

jumping, mountain climbing, or scuba diving. Thrill-seeking activities create a

“rush” of excitement—a positive feeling that may be related to the release of dopamine,

a neurotransmitter associated with physiological arousal. Given the possible

connection between dopamine and thrill seeking, one theory suggests that people

who are defi cient in dopamine will tend to seek out exciting situations as a way of

increasing their dopamine release and making up for defi cient levels of dopamine.

In the mid-1990s, researchers presented the fi rst genetic evidence to support

this theory. The gene DRD4 is involved in dopamine production in the limbic

system, and the longer the gene sequence, the less effi cient dopamine production is.

438 Part V Biological/Evolutionary Theories

In other words, long versions of the DRD4 gene are associated with less effi cient

dopamine production. If the theory is correct, people who seek out thrills should

have the longer form of this gene, and that is exactly what the research has shown

(Ebstein et al., 1996; Hamer & Copeland, 1998). An exciting aspect of this fi nding

is that it was the fi rst to demonstrate a specifi c genetic infl uence on a normal

(nonpathological) personality trait.

The second method used by behavioral geneticists for untangling the effects of

genetics and environment on personality was fi rst discussed in Chapter 14 (Eysenck),

namely twin-adoption studies . Recall that the conclusion from this research is that

between 40–60% of our personality differences stem from genetic infl uence

(Bouchard & Loehlin, 2001; Caspi, Roberts, & Shiner, 2003; Kruger & Johnson, 2008;

Loehlin et al., 1998; Plomin & Caspi, 1999; Tellegen et al., 1988). This line of research

therefore suggests that about half of the differences that exist between people in their

personalities is attributable to genetics, leaving the other half infl uenced by environment

or other unknown factors. These results are consistent with the view that personality,

intelligence, motivation, and other psychological qualities are products not only of

biological or environmental forces alone, but also of the interaction between the two.

In short, personality differences are created by both nature and nurture.

Animal Personality

Most of you who have ever owned pet cats or dogs would readily agree that your

pets have their own unique personalities. One of your authors (GJF), for example,

currently has two sibling cats, a male (Scooter) and a female (Belle). These two

kittens could hardly be more different in terms of their behavior and personality.

Scooter is absolutely curious and sociable. He explored every inch of his new home

on the fi rst day and forces himself into every one of our activities—eating, watching

TV, working at the computer, and sleeping. Not once has he been afraid of

any situation. He approaches everything with glee and wonder. Belle, however,

has been anxious and shy from the beginning. It took her about 3 days to come

out of hiding and become comfortable with her new home. She plays, but not so

much with strangers. She loves playing with her brother, however, and they regularly

tease and chase each other. Now she hangs out with the family and enjoys a

good massage, but she is still skittish to sudden approaches.

To pet owners the question of animal personality seems to have an obvious

answer: Of course, animals have distinct personalities. But to psychologists the

question might seem to be stretching the defi nition of personality too far. But even

if we can see evidence of personality in animals such as dogs and cats, can we see

it in other animals? What about birds? reptiles? fi sh? worms?

Until the 1990s, most psychologists would have argued that the term personality

made sense only as applied to humans, but since then numerous studies have supported

the notion that non-human animals not only have distinct personalities but they have

personalities on dimensions similar to the Big Five in humans ( Dingemanse, Both,

Drent, Van Oers, & Van Noordwijk, 2002; Gosling, 1998; Gosling, Kwan, & John,

2003; Weinstein, Capitanio, & Gosling, 2008). For example, Gosling and Oliver John

(1999) conducted a meta-analysis (quantitative review) of 19 studies across 12 nonhuman

species. They found evidence for at least 14 nonhuman species with personality

Chapter 15 Buss: Evolutionary Theory of Personality 439

traits that can be categorized along the same dimensions as human personality. The

summary of these fi ndings is presented in Table 15.4 . Keep in mind that the labels

from the Big Five are general labels, and the specifi c ones used in these studies vary

somewhat. For instance, neuroticism is sometimes called emotional stability, excitability,

fearfulness, emotional reactivity, fear–avoidance, or emotionality. Agreeableness

is sometimes labeled aggression, hostility, understanding, opportunistic, sociability,

affection, or fi ghting–timidity. In addition, dominance–submission is a trait that is

often seen and measured in nonhuman animals, but it does not fi t into any of the Big

Five categories. These ratings of animal personality were made by one of two behavioral

observation techniques: either by animal trainers who had extensive knowledge

of the individual animals or by trained observers with no history with the animals but

who were trained until they could reliably evaluate the dimensions in question.

It may not surprise you that primates and other mammals tend to share the

largest number of personality traits with humans (Weinstein et al., 2008). For

instance, chimpanzees, our closest relative, share with humans a distinct “conscientiousness”

dimension. Such a fi nding suggests that conscientiousness—which

involves impulse control and therefore requires highly developed brain regions

capable of controlling impulses—is the most recently evolved personality trait.

Thus, with the exception of chimps and horses, animals other than humans do not

possess the required brain structures to control impulse and organize and plan their

activities in advance. Even with chimps, the conscientiousness dimension was

T A B L E 1 5 . 4

Table of Personality Dimensions across Species

Personality Dimension

Species Neuroticism Extraversion Agreeableness Openness Conscientiousness

Chimpanzee ✓ ✓ ✓ ✓ ✓

Horse a ✓ ✓ ✓ ? ✓

Rhesus Monkey ✓ ✓ ✓ ✓

Gorilla ✓ ✓ ✓

Dog ✓ ✓ ✓ ✓ b

Cat ✓ ✓ ✓ ✓ b

Hyena ✓ ✓ ✓

Pig ✓ ✓ ✓

Vervet Monkey ✓ ✓

Donkey ✓ ✓

Rat ✓ ✓

Guppy (Fish) ✓ ✓

Octopus ✓ ✓

Chickadee c ✓

a Based on Morris, Gale, & Duffy (2002).

b Competence/learning is a mixture of openness and conscientiousness.

c Based on Dingemanse, Both, Drent, Van Oers, & Van Noordwijk (2002).

Expanded and adapted from Gosling & John, 1999.

440 Part V Biological/Evolutionary Theories

somewhat narrowly defi ned as lack of attention, goal directedness, and disorganized

behavior.

It may be surprising, however, to see wild birds, fi sh, and even octopus on a

list of animals that possess humanlike personality traits. For instance, in a study of

a European bird resembling a chickadee, when researchers placed a foreign object,

such as a battery or a Pink Panther doll, into the cage, some birds were consistently

curious and explored the novel object while others consistently withdrew and avoided

the object (Zimmer, 2005; cf. Dingemanse et al., 2002). The researchers called these

differences in birds “bold” and “shy.” These differences are much like those psychologists

observe when they place an infant in a room with a stranger. Approach–

boldness and shyness–avoidance are also dimensions of human temperament.

In sum, just as eyes, ears, brains, and thermoregulation are evolved solutions

and are shared between species and genera of animals, personality traits are shared

solutions and found in almost all animals from the invertebrates, fi shes, reptiles,

birds, and mammals (including primates). The more similar the genus and species,

the more similar the system—and this holds for personality. The personality structure

of primates is more similar than that of mammals in general, which in turn is more

similar than birds or invertebrates. This evidence supports the view that personality

traits evolved long before modern humans and have their origins in a common

ancestor millions of years ago.

Critique of Evolutionary Theory of

Personality

Evolutionary psychology in general and evolutionary personality psychology in

particular have stimulated a lot of controversy but also a relatively large body of

empirical research . The fi eld has its own scientifi c society (Human Behavior and

Evolutionary Society, HBES), and its own scientifi c journal, Evolution and Human

Behavior. The discipline also rests upon other scientifi c disciplines, such as evolutionary

biology, ethology, behavioral genetics, and neuroscience, so there is a

solid empirical foundation to the fi eld. Similarly, a quick search on GoogleScholar

generated more than 34,000 articles for the joint term “evolutionary psychology.”

The same GoogleScholar search on “evolutionary personality psychology” produced

660 articles between 1990 and 2012.

To the question of whether evolutionary personality theory is falsifi able the

answer is complex. Evolutionary theory in general is diffi cult to falsify in the strict

sense of the word (Stamos, 1996). Many critics of evolutionary theory are quick to

point out that the central tenets of evolutionary theory are inherently non-falsifi able

and untestable because evolution is a past event and it would take at least thousands

of years to observe the outcome of evolution in animals. Moreover, they argue that

evolutionary psychology is mostly after the fact (post hoc) explanations for any

given phenomenon—in short, evolutionary psychology produces plausible “just-so

stories” and many different plausible stories can always be constructed to explain

an evolutionary outcome (Gould & Lewontin, 1979; Horgan, 1995).

Yet, other scholars have argued this is both somewhat inaccurate and also not

completely the point. Defenders of evolutionary theory, for instance, have pointed

Chapter 15 Buss: Evolutionary Theory of Personality 441

out that defeating a theory by contrary facts (falsifi cation) is not the only way that

science proceeds (Ellis & Ketelaar, 2000; Ketelaar & Ellis, 2000). An alternative

criterion for scientifi c progress is whether it generates novel predictions and explanations.

By this standard, evolutionary theory does quite well.

In terms of how well evolutionary theory of personality organizes known

knowledge , we would argue the theory rates quite highly. Evolutionary theory is very

broad and long-range in its scope and in that sense it provides a range of explanations

seldom seen in social science. It offers explanations for the ultimate origins of

not only all biological systems, but human thought, behavior, and personality as well.

As a guide for practitioners however, we give the theory relatively low

marks. Evolutionary theory says little about how we should raise our children, what

we should teach them and how, or how to conduct therapy to treat mental disorders.

The theory is more abstract and pure than concrete and applied.

Evolutionary theory of personality rates moderate on internal consistency.

Adaptation is a guiding principle and many ideas stem from this core concept. And

most scholars agree on how to defi ne adaptation. However, not all agree on what

is and is not an adaptation. The most glaring example is personality. Although

Buss, MacDonald, and Nettles all agree that personality variability is an adaptation,

two other leading theorists, Tooby and Cosmides, do not.

Evolutionary theory of personality scores high on the criterion of parsimony .

The idea that you can explain the origins of human personality with a few key

concepts of adaptation, mechanism, and natural and sexual selection is quite simple.

Concept of Humanity

It is diffi cult to say on which side of the optimism-pessimism debate evolutionary

theory would fall. It is mostly descriptive and, in that sense, tends to be

somewhat neutral about describing human nature. Humans are and have been

capable of incredibly uplifting acts of heroism and bravery and cooperation,

inspiring works of creativity, and unbelievable and unspeakable acts of violence

and cruelty. Both extremes are part of human nature (Pinker, 2002).

Evolutionary psychology has a complex view on the question of determinism

versus free-will . A common assumption of evolutionary theory by critics is that

it is harshly deterministic in that it explains behavior in terms of an evolved

past and genetic infl uence. Indeed, evolutionary psychology is often criticized

for condoning traditional sex-roles (e.g., women are attracted to high status men

and men are attracted to physically attractive women). Buss and other evolutionary

theorists make clear, however, that evolutionary psychology is a theory of

how these traits began, not how they should be. In other words, it is meant to

be more descriptive than prescriptive. Moreover, as we saw with Buss’s view of

the origin of personality, biological and environmental explanations are not

mutually exclusive. They are both necessary. Buss (1999) argues in fact that

knowledge and awareness of our evolved psychological mechanisms and strategies

actually give us more power to change them if we want to.

On the question of causality versus teleology it is clear that evolutionary

theory comes down heavily on the causality side of the equation. Evolution by

natural selection above all else is a theory of origins or cause. Darwin’s book,

after all, was titled Origin of Species.

Evolutionary theory sides more with the unconscious infl uences on thought,

behavior, and personality than on conscious ones. Most of what we do is inherently

beyond our conscious awareness, and this is particularly true of evolutionary

origins and strategies that shape our behavior. We are no more aware of why

we prefer sweet and fatty to bitter than we are of why we are attracted to one

person over another. Similarly, we have no idea why we might be anxious and

sensitive to stress while someone else is calm and collected under duress.

In fact, one reason why people may resist evolutionary accounts of behavior,

much as they resisted Freud’s ideas, is that it makes the unconscious conscious

and people’s conscious ideas for why they do what they do, like what they

like, and are driven by what they are driven by are almost always at odds with

the evidence from science in general and from evolutionary psychology and biology

in particular. And yet, we don’t have to be aware of how eyes or hearts

evolved in order to use them. We just use them. Similarly, we just act, think,

feel, and are motivated. Awareness is not necessary and in many cases would be

very disruptive.

The concept of humanity that will be most surprising to many people will

be evolutionary psychology’s stance on biological versus social infl uence . Clearly

there is a strong emphasis on biological infl uences, from brain systems, neurochemicals,

and genetics. But as we have made clear in the chapter, evolved

mechanisms can only operate with input from the environment. Therefore, evolutionary

theory is completely balanced on the question of biological versus

environmental causes of personality.

Evolutionary theory is also balanced on the question of the uniqueness of

the individual compared to general commonality among all people. The structure

of evolved mechanisms, that is, which mechanisms operate, are species typical

and universal, but the content of the mechanisms is unique and shows tremendous

differences between individuals.

442 Part V Biological/Evolutionary Theories

Key Terms and Concepts

• Artifi cial selection (otherwise known as “breeding”) occurs when humans

select particular desirable traits in a breeding species.

• Natural selection is the process by which evolution happens and is simply

a more general form of artifi cial selection in which nature rather than

people select the traits.

• Sexual selection operates when members of the opposite sex fi nd certain

traits more appealing and attractive than others and thereby produce

offspring with those traits.

Chapter 15 Buss: Evolutionary Theory of Personality 443

• Adaptations are evolved strategies that solve important survival and/or

reproductive problems. Adaptations are often the products of natural or

sexual selection and must have a genetic or inherited basis to them.

• By-products are traits that happen as a result of adaptations but are not part

of the functional design.

• Noise, also known as “random effects,” occurs when evolution produces

random changes in design that do not affect function. Noise tends to be

produced by chance and not selected for.

• The term evolutionary psychology can be defi ned as the scientifi c study of

human thought and behavior from an evolutionary perspective and focuses

on four big questions.

• The process of evolution by natural selection has produced solutions to two

basic problems of life—survival and reproduction—and they are called

mechanisms . More specifi cally, mechanisms operate according to principles

in different adaptive domains, number in the dozens or hundreds (maybe

even thousands), and are complex solutions to specifi c adaptive problems.

• 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 reproductive problems.

• Psychological mechanisms relevant to personality can be grouped into

three main categories: goals/drives/motives, emotions, and personality

traits. They are adaptive because they help solve problems of survival and

reproduction.

• Buss’s model of personality very closely resembles the Big Five trait

approach of McCrae and Costa but it is not identical in structure:

Surgency/extraversion/dominance, Agreeableness, Conscientiousness,

Emotional stability, and Openness/Intellect . Buss argues these behavioral

dispositions have adaptive signifi cance.

• The two main sources of the origin of personality are environment and

genetics.

• There are still numerous misunderstandings of evolutionary theory,

including the idea that evolution implies genetic determinism or that

mechanisms are always optimal designs.