Chapter 5: Biological Aspects of Personality

Evolutionary Psychology

• Posits that natural selection has led to the development of certain identifiable, genetically-based characteristics that affect personality and social behavior.

Natural selection: 

Some characteristics lead to increased reproductive success of the organism. Hence, greater probability of survival of the species.

Over successive generations, more adaptive characteristics are favored. Less adaptive characteristics are weeded-out.

Based on the theory of evolution by Charles Darwin.

Heritability: a measure of the proportion of variability of a trait, within a population, that is associated with genetic variability.

Typically estimated from studies of twins and family studies.

Most personality traits have substantial heritable components.

On average, about h = 0.50 for most traits.

That also suggests about 50% of variability in most traits is not heritable (i.e., due to other factors).

Learning.

Environment.

Temperament

Stable individual differences in emotional reactivity.

Typically apparent early in life, even in infancy.

Underlying differences in nervous system response to environmental stimuli.

Four basic dimensions of temperament.

Activity: active and in motion vs. passive.

Emotionality: easily aroused to anger, fear, or other emotions vs. more emotionally calm.

Sociability: tendency to approach and enjoy others vs. being withdrawn.

Aggression/Impulsivity: aggressive & cold vs. conscientious & friendly.

Eysenck’s CNS Model of Temperament 

Introversion-Extraversion:

Introverts: quiet, reserved, thoughtful.

Extraverts: active, sociable, outgoing.

Most people are somewhere in-between.

Combines elements of activity & sociability.

1960s: Hans Eysenck proposed that CNS differences account for introversion-extraversion.

Introverts: Have greater CNS arousal. Hence, they seek less stimulation.

Extraverts: Have less CNS arousal. Hence, they seek more stimulation.

Extroverts show less arousal on measures of electrodermal activity.

Electrical activity on surface of skin.

Extroverts show less CNS arousal on electroencephalograph (EEG).

Introverts slower to habituate to (get used to) sensory stimuli (e.g., loud noises).

More easily bothered by intense stimuli.

Gray’s Reinforcement Sensitivity Theory 

Jeffrey Gray (80s & 90s): Two bio-learning systems.

Behavioral Activation System (BAS):

Regulates person’s response to rewards & pleasurable stimuli.

Overactive BAS: Impulsive, reward-seeking, sensation-seeking. (Ex: more prone to drug addiction & overeating).

Behavioral Inhibition System (BIS):

Orients person to novel situations.

Responds to things that are punishing or aversive.

Overactive BIS: Anxious, alert, worrying.

Conceptualization:

Impulsive ppl more motivated by reward.

Anxious ppl more motivated by unknown or aversive stimuli.

Cloninger’s Tridimensional Model 

• C.R. Cloninger (1980s).

• Three biologically-based personality traits.

• Each related to functioning of a specific neurotransmitter (NT) in the central nervous system (CNS).

• Novelty seeking:

Related to tendencies to:

Become excited in response to novel stimuli.

Explore one’s environment.

Trying new things for thrill or excitement.

Inversely related to dopamine.

Related to the Behavioral Activation System (BAS).

Higher among substance abusers.

• Harm avoidance:

Tendency to worry and feel tense.

Related to the Behavioral Inhibition System (BIS).

Influenced by aversive stimuli and signals of punishment.

Low HA is related to impulsivity & aggression.

Positively related to serotonin.

Reward dependence:

Behavioral maintenance system.

Tendency to continue behavior that produces reward.

Tendency to be persistent or hard-working.

Inversely related to norepinephrine.

Criticism of the Biological Viewpoint