Biological Basis of Personality:Genetics and twins studies

123 pairs of identical twins and 127 pairs of fraternal twins

Measured on “Big Five” personality dimensions

Results suggest that personality differences in the population are 40 - 60% heritable.

The personality of adopted siblings No more alike than randomly selected persons Largely unrelated to adoptive parents

Doesn’t parenting style affect adult personality? Peers, not adults, exert the most influence on

personality (Rowe, 1994; Harris, 1998) But a minimum amount of parenting is critical for the

avoidance of antisocial behavior (Lykken, 2000)

Biological Basis:Genetics and adoption studies

Biological Basis: Specific genes for specific traits?

A gene that regulates a particular dopamine receptor is associated with novelty seeking One form of this gene produces deficiency in dopamine and

people seek out novel experiences to increase the release of dopamine, which is related to feelings of reward and pleasure

A gene that regulates serotonin is associated with neuroticism and agreeableness

However, typically, a personality trait will be a product of many genes and the presence of an environment appropriate for gene expression

Biological Basis: Temperaments in Infancy

Temperament A general tendency to feel or act in a certain way that is strongly linked

to biology If infants show such tendencies, these tendencies must be “hard-wired”

(i.e., must be biological) since the environment has not yet had a chance to exert its influence

Shyness (Kagan & Snidman, 1991) 15-20% of newborns (as young as 6 weeks) respond to new situations or

strange objects by becoming distressed (i.e., crying, etc.) At 4 years old, these children are described as shy by their parents Likely to be shy as a teenager More likely to be depressed as a young adult

The Neurophysiological Mechanisms of Extraversion

Extraversion Less than optimal levels of activity in the ascending reticular

activating system (part of the brain stem) Chronic underarousal leads extraverts to seek stimulation Extraverts work and perform better in noisy environments

The behavioral approach system (BAS) is stronger in extraverts

The BAS leads organisms to approach stimuli in search of rewards Extraverts have heightened dopamine activity in the reward center of

the brain (i.e., the nucleus accumbens, a part of the limbic system) Extraverts report high levels of energy, desire, and self-confidence

The Neurophysiological Mechanisms of Introversion

Introversion Greater than optimal levels of activity in the ascending

reticular activating system (part of the brain stem) Chronic overarousal leads introverts to avoid stimulation Introverts are more sensitive to stimulation, including pain

The behavioral inhibition system (BIS) is stronger in introverts

The BIS is sensitive to punishment and leads organisms to inhibit behavior that might lead to danger or pain

Introverts have heightened activity in the frontal lobes (which are known to inhibit socially inappropriate behavior) and in the amygdala (which processes stimuli related to punishment and fear)

Introverts are anxious about social situations because they fear negative outcomes

Personality Is Evolutionarily Adaptive

Natural selection has shaped the human genome over the course of evolution.

Adaptive personality traits were passed along to increasing numbers of individuals in future generations.

For example, It is easy to imagine how being competitive might lead a person to obtain great rewards and how being competitive would be passed on.

But if traits are adaptive, why are there such great individual differences among people?

Natural selection ought to make people more similar rather than more different. Individual differences may be the result of evolution having endowed us

with multiple strategies for survival The strategy an organism selects depends on the particular environment

For example, a competitive person in a cooperative society (or a cooperative person in a competitive society) would have a distinct advantage

Such diversity within a group may confer a selective advantage over groups that have less diversity

For example, it may be good for a group to have both competitive and cooperative members Competitive individuals often risk their physical well-being and hence do not survive, while

cooperative members do

Personality Consistency over Time

In general, personality is consistent over the lifespan

Where you rank relative to others on personality traits changes relatively little over time.

This supports the notion that traits are hard-wired

However, is personality more consistent at some points in the lifespan?

Evidence indicates that personality is least stable during childhood

Consistency increases with age

Personality Change over Time

Your rank order relative to others on the trait of conscientious changes relatively little over time

If you’re very conscientious relative to others when you’re 20 years old, the same will likely be true when you’re 50 years old

However, conscientiousness in everyone tends to increase over time

This is true in multiple cultures

Levels of personality (McAdam):Some change, some don’t

Dispositional traits (or basic tendencies) The Big Five Not likely to change in a particular individual over time

Personal concerns These, and the strategies we use to meet them, change according to

situation or developmental stage However, even though the particular concerns and strategies change,

the way they change corresponds to a person’s basic tendencies Thus, these changes are often called characteristic adaptations

Life stories These evolve over time to provide a person’s life with a sense of unity

and meaning For example, someone might see themselves as having a “rags to riches” life

story

Personality change: Brain injury and psychological medications

Phineas Gage Alzheimer’s disease

There is some evidence that personality changes are the first signs of early stage Alzheimer’s (Moran et al., 2004)

Prozac Antidepressant that works by increasing the activity of

serotonin When taken by individuals without depression, it can cause

personality changes, such as Increased social dominance and extraversion Decreased hostility and neuroticism

The self: Self-awareness

Self-concept Who you think you are. Influences your daily choices.

Self as “I” (knower) vs. self as “me” (known) The knower is you thinking, feeling, making decisions, etc. The known (the objectified self) is the knowledge you hold about your self; your

self-concept Self-awareness theory

The “I” thinking about the “me” We spend only about 8% of our time thinking about ourselves.

Objective self-awareness pushes us to act in accordance with our self-concept Self-discrepancy is the awareness that we are not acting in accord with our self-

concept This realization can generate negative emotions within ourselves See next slide

Self-Awareness Theory

Self-Conscious Persons

Self-focusing situations

Self-Awareness

Change Behavior to Match Standards

Self-Discrepancies

Escape from Self-Awareness

Escape from self-awareness is sometimesaccomplished through the consumption of alcohol. Thiscan also provide an excuse for future failures.

The self: Self-schema

Self-schema The cognitive component of our self-concept The working self-concept

The immediate (present moment) conception of our self This can change from situation to situation

That is, the working self concept is formed “on-line” Independent vs. interdependent self-construals

People that live in individualistic cultures tend to have independent self-construals

In an individualistic (typically Western or industrialized) culture, personal goals and preferences take priority over group allegiances.

People that live in collectivist cultures tend to have interdependent self-construals

In a collectivist (typically Eastern or agrarian) culture, cooperation and group harmony take priority over purely personal goals.

See the next two slides

The self: Self-esteem

Self-esteem The evaluative or emotional component of the self-concept

Am I worthwhile or worthless? Good or bad? Reflected appraisal

In large part, people view themselves as others view them. Sociometer theory

When a person behaves in ways that lead to rejection by their social group, their self-esteem will be reduced.

Terror management theory Exaggerations of personal importance reflect attempts to buffer anxiety about

inevitable death. Self-esteem is only weakly related to objective life outcomes.

Although people with high self-esteem do report more happiness. There are some downsides to having high self-esteem.

When some people with high self-esteem are challenged, they can become bullying, violent, or boastful.

The Self-Esteem Cycle

High Self-Esteem

Self-Credit

Success High Effort

Positive Expectations

Low self-esteem and negative self-evaluations are related to pessimistic explanatory styles, which in turn are related to negative consequences for the immune system.

The self: Positive illusions

People think of themselves in overly favorable terms The better-than-average effect.

Most people describe themselves as above average in almost every way. Self evaluative maintenance

Self-esteem is influenced by An individual’s performance How relevant that performance is to that individual’s self-concept How that performance compares to the performance of people that are

significant to that individual Social comparison

People with low self-esteem tend to make upward comparisons with others that are superior to them.

Self-serving bias People with high self-esteem take credit for success, blame failures on

outside factors, and attribute criticism to envy or prejudice.