Biological Foundations of Personality

• Biological explanations for personality differences focus on three

levels.

1. one group of theorists uses evolutionary principles to explain why

particular traits exist in the human species (e.g., Buss, 1999).
2. Others seek the genetic bases for trait inheritance (Plomin, 1997).
3. And others search for differences in the functioning of the nervous
system (Heatherton et al., 2004; Pickering & Gray, 1999).
Evolutionary Perspective
• Evolutionary personality theory tries to explain where universal
personality traits came from
• Evolution usually explains similarities among humans, but this theory
also explains individual differences.
• The big 5 traits show up in almost all cultures, suggesting they are
universally human.
• According to David Buss (1999), these traits evolved because they
helped in:
• Physical survival
• Reproductive success
Lewis Goldberg (1981) said humans evolved to ask key questions when
meeting others:
1.Is the person dominant or submissive? → relates to Extraversion
2.Is the person friendly or hostile? → relates to Agreeableness
3.Is the person reliable? → relates to Conscientiousness
4.Is the person stable or unstable? → relates to Neuroticism
5.Is the person smart and adaptable? → relates to Openness
• → These basic survival questions match the Big Five, which is why
these traits are consistent across cultures.
How each trait helped humans survive and reproduce:

• Extraversion & Emotional Stability:

• Helped gain dominance, attract mates.
• Example: A confident, outgoing person could lead a group and attract more
partners.
• Agreeableness & Conscientiousness:
• Helped in group survival and raising children.
• Example: A dependable and kind person would be trusted, get support, and
raise children well.
• Openness to Experience:
• Helped with problem-solving, creativity, and adapting to changes.
• Example: Creative thinkers could invent tools or solve group problems,
increasing survival chances.
Strategic Pluralism: Why Differences are Good
• It’s the idea that different traits can be useful in different environments.
• So, variation is adaptive, and natural selection keeps multiple strategies.
➤ Examples of trade-offs in Big Five traits:
• Extraversion (Nettle, 2006):
• Benefits: More sexual partners, social success, support, fun, adventure.
• Example: An outgoing man may attract many mates and have lots of offspring.
• Costs: More risk of accidents, illness, or antisocial behavior (which can lead to punishment or death).
• For women: Might lead to impulsive, risky relationships.
• Agreeableness:
• Benefits: Peaceful relationships, social support.
• Costs: Can be exploited, or may not push for own goals.
• A little selfishness can be adaptive.
• Neuroticism:
• Usually seen as bad (anxiety, stress, illness).
• But also useful: Helps detect danger, avoid harm, and push for success.
• Example: A cautious person might avoid poisonous food or dangerous animals.
• → These trade-offs explain why people vary in personality. What works in one situation might not work in
another.
Genetics and Personality
• Twin studies are particularly informative for studying the role of genetic
factors because they compare the degree of personality resemblance
between monozygotic twins, who have identical genetic makeup, and
dizygotic twins, who do not (Lykken, 2006; Rowe, 1999).
• identical twins are more similar to each other than are fraternal twins,
suggesting a role for genetics.
• However, the issue is clouded by the possibility that identical twins may
also have more similar environments than fraternal twins because others
are inclined to treat them more similarly.
• The ideal solution to this problem would be to compare personality traits
in identical and fraternal twins who were raised together and those who
were separated early in life and raised apart.
• If the identical twins who were reared in different families were as similar
as those reared together, a more powerful argument could be made for the
role of genetic factors.
Minnesota Twin Study (Auke Tellegen & team)
• Famous study (includes the Jim twins—identical twins raised apart but super similar!)
• Researchers gave 14 personality trait tests to four twin groups:
• Identical twins raised together
• Identical twins raised apart
• Fraternal twins raised together
• Fraternal twins raised apart
Key Findings:
1.Genetic influence explained 40–50% of personality trait differences.
Example: If you’re very outgoing and your twin is too, that might be due to genes.
2.Family environment (shared) had very little effect.
Whether twins were raised together or apart didn’t change much—surprisingly, family
background (rich/poor, loving/strict) had little impact on personality similarity.
3.Unique environmental experiences matter a lot. ➤ Things like:
1. Different friends
2. Different teachers
3. Different challenges
These shape personality individually, even in the same family.
Personality and the nervous system
• Hans J. Eysenck (1916–1997), one of Britain’s leading psychologists,
maintained that normal personality can be understood in terms of
only two basic dimensions. These dimensions of Introversion
Extraversion and Stability-Instability (sometimes, as in the Big Five,
called Neuroticism) blend together to form all of the more specific
traits. Eysenck’s two “supertraits” are comparable to the Big Five
traits of Extraversion and Neuroticism.
• He suggested that the two basic dimensions intersect at right angles,
meaning that they are statistically independent, or uncorrelated.
• He linked Introversion-Extraversion and Stability-Instability to
differences in individuals’ normal patterns of arousal within the brain.
• He started with the notion that there is an optimal, or preferred, level
of biological arousal in the brain.
• Eysenck believed that extreme introverts are chronically overaroused;
their brains are too electrically active, so they try to minimize
stimulation and reduce arousal to get down to their optimal arousal
level, or comfort zone.
• In contrast, the brains of extreme extroverts are chronically under
aroused, so they need powerful or frequent stimulation to achieve an
optimal level of cortical arousal and excitation.
• The extrovert thus seeks social contact and physical arousal, likes
parties, takes chances, is assertive, and suffers boredom easily.
• Whereas Introversion-Extraversion reflects a person’s customary level of
arousal, Stability Instability represents the suddenness with which shifts in
arousal occur.
• Unstable people have hair trigger nervous systems that show large and
sudden shifts in arousal, whereas stable people show smaller and more
gradual shifts (Pickering & Gray, 1999).
• Eysenck also called this stability dimension Neuroticism because he found
that people with extremely unstable nervous systems are more likely to
experience emotional problems that require clinical attention.
• Studies show identical twins are more similar on these traits than fraternal
twins. Around 50% of personality variance is genetic (Loehlin et al.,
Plomin).
• Modern Research & Brain Imaging confirms Eysenck’s idea of biological
roots of personality.
• Different brain regions are active for different traits (Canli, 2004).
Temperament : Building blocks of Personality

• Temperament refers to individual differences in emotional and

behavioral styles that appear so early in life that they are assumed to
have a biological basis. Such temperamental factors as emotionality,
activity level, sociability, and impulsivity are visible even in infancy
(Buss & Plomin, 1975, 1984).
• It influences the subsequent development of personality. The fact
that these temperamental factors are more highly correlated in
identical than in fraternal twins suggests a genetic link (Buss &
Plomin, 1984).
• Recent research has focused on biological differences in inhibited and
uninhibited people.
• First identified by Jerome Kagan (1999) on the basis of behavioral
observations and biological function ing, inhibited infants and children are
shy, restrained in their behavior, and react to unfamiliar people and
situations with distress and avoidance. In contrast, uninhibited children
respond positively to new situations and people and seem to enjoy novelty.
• About 20 percent of infants are inhibited, and about 40 percent are
uninhibited.
• Kagan (1999) found that these temperamental patterns can be identified in
the first 4months of life and that they persist into later child hood in many
(but not all) children.
• These two groups of children also differ physiologically, with the inhibited
children showing higher levels of physiological arousal and stress-hormone
secretion in response to unfamiliar situations and people.
• Recent research sheds light on brain regions that contribute to inhibited
and uninhibited tendencies. One important region is the amygdala, the
structure in the limbic system that organizes fear responses.
• Kagan suggested that the amygdala was involved in the physiological
overreactivity he measured in inhibited children.
• In a more recent study, fMRI brain recordings were taken in young adults
who had been categorized as either highly inhibited or as uninhibited when
they were 2 years old (Schwartz et al., 2003).
• Of interest was how their amygdala would react to pictures of familiar and
unfamiliar human faces. those adults who had been uninhibited as children
showed relatively low amygdala reactivity to both familiar and novel faces,
whereas the formerly inhibited participants showed particularly high
reactivity to the novel faces. This study thereby demonstrated a negative
response to novel stimuli in inhibited people that extended from childhood
to adulthood, as well as a possible biological basis for this tendency.
Strengths of the Biological Perspective

1.Scientific Evidence (Twin & Adoption Studies)

1. Shows that genetics play a big role in traits like extraversion, neuroticism, etc.
2. Example: Identical twins are more similar in personality than fraternal twins.
2.Brain and Biological Basis
1. Links traits to specific brain structures and neurochemical activity.
2. Example: Eysenck linked extraversion to arousal levels in the brain cortex.
3.Consistency Across Cultures & Lifespan
1. Traits like temperament appear early and stay stable over time and across cultures.
2. Example: Inhibited/uninhibited traits seen in babies worldwide.
4.Objective Methods
1. Uses brain scans, physiological data, genetic testing — all measurable and
scientific.
Limitations of the Biological Perspective

1.Underestimates Environmental Influence

1. Ignores how much life experiences, culture, and upbringing shape personality.
2. Example: A shy child may become outgoing with the right support.
2.Too Deterministic
1. Suggests personality is pre-programmed by biology, leaving little room for change
or free will.
3.Simplifies Complex Behavior
1. Reduces personality to just genes and brain functions, ignoring emotions, goals, and
thoughts.
4.Hard to Prove Causation
1. Correlation ≠ causation. Just because brain differences are seen doesn’t mean they
cause the personality trait.