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Genetics, Evolution, &
Personality
Timothy C. Thomason
Northern Arizona University
Why Do People Differ in Personality?
• Genetics (nature)
• Environment (nurture)
• Nature and nurture interact and have
reciprocal effects
• Can people change their personalities?
Eg. Can a shy person become outgoing?
• Implications for self-improvement, therapy
Behavioral Genetics
• Physical attributes are inherited; why not also
psychological attributes?
• Genes do not influence behavior directly (eg.,
there is no gene for extraversion).
• But genes influence behavior indirectly by
affecting biological functioning.
Eg. nervous system; hormones; etc.
Heritability of Personality
• Twin studies and adoption studies
• Studies of identical twins reared apart
• Genetics is more important than heredity
– Correlations for identical twins are twice as large
as those for non-identical twins.
– Every personality trait studied has been found to
have substantial heritability.
• Between 40% and 60% of the variability in
personality is due to genetic factors.
• Studies of identical twins reared apart who had
never met were found to have almost identical
vocational interests, hobbies, and pets.
• Note that heritability estimates apply to
populations, not individuals (they imply a
statistical probability).
The Influence of Environment
• Estimated to be about 40%
• On average, the correlation for personality
traits between non-twin siblings brought up in
the same household is nearly zero.
• Biological siblings raised together are no more
similar than those raised apart.
Summary: What Causes Personality?
• Genetics
50%
• Environment
40%
(Measurement error 10%)
But remember that these are rough
estimates, and that genes and the environment
interact in a complex manner, so assigning
percentages is simplistic.
Examples of Genetic/Environment
Interactions
• An attractive child may evoke different
reactions from parents than a non-attractive
child. Being treated as attractive may affect
the child’s self-esteem and their personality.
• An agreeable, friendly child may cause parents
and peers to respond differently compared to
a child with a disagreeable disposition.
The Nature/Nurture Debate is Dead
• It is always both nature and nurture.
• The relative contribution of each often
depends on the specific circumstances.
Molecular Genetics
Molecular genetics attempts to find causal
links between genes and personality traits.
Eg. Research has identified a mutation in the
serotonin transporter gene associated with
individual differences in trait anxiety.
Eg. There is an association between the D4
dopamine receptor gene and sensation-seeking.
Sensation-seeking may be an attempt to
compensate for lower levels of dopamine.
Genetic Profiling
• Single genes can cause physical diseases.
Eg. Mutation of the HTT gene & Huntington disease.
• But complex personality traits reflect the
operation of multiple genes.
• We should not expect to find specific genes
for specific personality traits.
• The link between genes and behavioral
tendencies is not direct.
Evolution and Personality
• Since personality is at least partly heritable,
we know it has a genetic basis.
• But why is there a genetic basis to
personality?
• The answer is evolution.
Evolution by Natural Selection
• Over time there is genetic variation in
inherited traits within a species.
• This variation occurs over a number of
generations.
• Genes that promote the survival and
reproduction of the organism are passed on to
the next generation.
• Genes that are harmful or have no adaptive
significance are gradually eliminated.
Adaptation
• Genes are subject to natural selection. After
thousands of generations, the genes that
survive are likely to be the good ones.
• New species usually develop due to accidental
geographic separation.
• There are now about 30 million species on
earth (1% of the species that have ever lived).
• Many current species will go extinct.
The Genetic Code
In all living organisms, the instructions for
reproducing and operating the individual are
encoded in a chemical language with four letters
(A, C, T, G: the initials of four chemicals).
Combinations of these letters (chemicals)
specify each of the amino acids that cells use to
build proteins.
Our Common Ancestor
• Studies in molecular genetics show that genes
can be traced back through the history of all
living organisms.
• Since all living things have the same genes,
they all must have descended from a single
ancestor. We share certain genes with chimps,
dogs, frogs, birds, insects, worms, yeast, etc.
• Human genes separated from chimpanzee
genes about seven million years ago.
Evolution
• Evolution over short time periods is easy to
understand.
• Evolution over long time periods is difficult to
understand, and contrary to our everyday,
commonsense ideas about our origins.
Evolution Explains A Lot
• A full understanding of human behavior
requires an understanding of human origins.
• All living organisms have innate tendencies.
Eg. Dogs act like dogs, not cats or lizards.
• Human behavior today is partly a result of
behaviors that evolved in our ancestors and
enabled them to pass their genes on to us.
Environment is the other major influence.
• The behaviors of our ancestors are not passed
on to us, but the genes that predisposed those
behaviors are.
• Most genes promote survival (otherwise they
would have died out).
• Some genes are artifacts; some are random
variations (mutations); and some are harmful.
Genetics Explains Why We Die
• The genes of all living organisms promote
reproduction (without reproduction, the
species dies).
• After the organism has lived long enough to
reproduce, living longer is irrelevant to the
continuation of the species.
• Genes age, errors and waste materials
accumulate, and eventually the organism dies.
Evolution Explains Many Human
Behaviors
• Evolutional psychology and toilet training.
Humans are much smarter than dogs and cats, but
dogs and cats can be potty-trained in a few days or
weeks, while human babies take years to learn it.
Why?
The ground-dwelling ancestors of dogs and cats had
to hide their feces to avoid attracting predators.
Human ancestors evolved in the trees, and tidy
potty habits simply were not an issue for them.
The Human Mind Evolved to Solve
Problems in Adaptation
• Problems of survival
Food shortages, harsh climate, disease, parasites,
predators, natural hazards
• Problems of reproduction
Competition for a mate; mate selection; successful
conception; mate retention; coalition building;
parental care; kin investment; etc.
Limits of Human Cognition
• The human mind did not evolve to solve
abstract problems unrelated to survival and
reproduction.
• This explains why we have so much difficulty
visualizing and understanding some topics.
– Evolution
– Quantum mechanics
– Cosmology
Innate Limits on Learning
• Operant conditioning has its limits.
– Eg. Raccoons can’t be trained to save money.
• Limits on operant conditioning:
– Biological limits
– Species-specific behaviors
– Innate predispositions
Evolution Explains Phobias
• Humans are not afraid of many things in our daily
environment today.
• Common human phobias:
– Dangerous animals (eg., snakes and spiders)
– High places, cramped places, and dark places
• Human phobias formed when our ancestors were
arboreal.
• Natural selection favored our innate
predisposition to fear certain stimuli that
reflected legitimate survival needs.
Fears and Phobias
• Many of our fears in the modern world are
irrational (but evolved for good reason).
• We have little fear of the things that are
actually dangerous.
• Which of the following is the most dangerous?
– Terrorism
– Rattlesnakes
– Driving a car
Environment of Evolutionary
Adaptedness (EEA)
• EEA is the environment our ancestors lived in
for about seven million years (hunting and
gathering in difficult environments).
• Agriculture is only about 10,000 years old.
• Many of the genes underlying our behavior
may not be suited to our lives today.
Eg. Our love of sugar and fatty meats.
Natural Selection & Personality
• Most of the biological and psychological traits
that exist in the human species today exist
because they have been adaptive to survival and
reproductive success.
For example, Extraversion is good for attracting
mates. Agreeableness is good for group harmony.
So why haven’t introversion and disagreeableness
been eliminated in the human species?
Why Are There Individual Differences
in Personality Traits?
• Differences in personality traits may reflect
differences in adaptive strategies that are
specialized for domain-specific problems.
• Example: negotiation of status hierarchy.
– Extraverts offer friendship and benefits.
– Conscientious people use hard work and
persistence.
– People who have low Agreeableness tend to use
deceit and manipulation.
• In evolutionary terms, in negotiating
dominance hierarchies, low Agreeableness
may be adaptively superior to high
Agreeableness.
• Individual differences in Agreeableness may
be seen as strategies to cooperate or act
selfishly, both of which are evolutionarily
adaptive and therefore likely to endure.
• Genetically based personality differences may
be adaptive to different environments and
contexts.
Eg. Introversion may be superior in structured
low-risk settings, while extraversion may be superior
in social situations where initiative and risk are
required.
The Five Factors As Adaptations
Humans have evolved special sensitivity to
variations in
– The ability to bond with others (Extraversion)
– The willingness to cooperate (Agreeableness)
– The tendency to be reliable and ethical
(Conscientiousness)
– The capacity to be a creative problem solver
(Openness to experience)
– The ability to handle stress (low Neuroticism)
Does a Baby Have a Personality?
• If personality is strongly influenced by genes,
does that mean a person is born with a certain
personality?
• Parents often describe individual differences
between their children (eg. in energy,
interacting with strangers, shyness, etc.).
Temperament
• Temperaments are individual differences in
behavior that appear early in life.
• There is no way to test a baby for personality.
• But it is possible to use ratings by parents,
observing reactions to novel stimuli etc.
Three Types of Temperaments
• Difficult babies.
• Easy babies.
• Slow-to-warm-up babies.
Three Dimensions of Temperament
• Emotionality
How easily the baby gets distressed
• Activity
Pace and power of motor movements
• Sociability
Responsiveness to other people
Temperaments & Personalities
• These dimensions may be precursors to the
adult personality structure (eg. FFM).
– Emotionality = Neuroticism?
– Activity/sociability = Extraversion?
– Task persistence = Conscientiousness?
– Adaptability = Agreeableness & Emot. Stability?
• Longitudinal studies have found a clear link
between childhood differences in
temperament and later differences in adult
personality.
Eg. Difficult babies had difficulties in adjusting
in adulthood, and easy-going babies found it
easier to adjust in later years.
Personality is fairly stable from birth to
adulthood.
Stability vs. Change
• The concept of personality rests on the idea of
stability over time and across situations.
• Research shows a high degree of stability in
personality across the life span.
Eg.A person who scores high on Extraversion at
age 30 is highly likely (83% chance) to score high on
Extraversion at age 50 or older.
Stability with Aging
• Stability increases as people get older.
• According to Costa & McCrae, “by age 30,
personality is essentially fixed.”
• Although there is some change in personality
after age 30, change is less likely to occur as
you get older.
• As people get older their environments tend
to become more stable. Their preferences for
food, friends, careers, and hobbies are not
likely to change dramatically.
• Couples who have similar personality profiles
experience less personality change than
couples who are less similar to each other.
• To change your personality, marry someone
who has your opposite personality profile.
Stability
• There is considerable stability in personality.
• There are many sources for this stability.
• Stability is high in older people but not
necessarily in younger people.
• Significant personality change can occur even
during late adulthood (but it is unlikely).
Changes in the Five Factors
• As people get older they become more
emotionally stable, more conscientious, and
more agreeable, and less extraverted and less
open to experience.
• As people get older they become calmer, less
confrontational, less risk-averse, more
reserved, and less open-minded.
• Thus, change does occur with age, but most
people change in the same ways.
Bibliography
Ahmetoglu, G. & Chamorro-Premuzic, T.
(2013). Personality 101. NY: Springer.
Dawkins, R. (1995). River out of Eden. NY: Basic
Books.
Ellis, A. & Abrams, M. (2009). Personality
theories. Thousand Oaks, CA: Sage.
McAdams, D. (2006). A new big five. American
Psychologist, 61(3).