Lecture 10

Biological Basis of Personality

• Where
• do personality traits come from?
• Two kinds of influence:
• Environmental:
• Shared
• environments - the family (shared and non-shared)
• Non-shared
• environments – include peers and school
• Biological:
• Evolutionary
• Theory of Personality.
• Genetics
• and personality
• Temperament
• and Personality.
• ---Hans Eysenck - The Ascending Reticular Activating
• System (ARAS).
• ---Gray’s and Cloninger’s
• biological models of personality
• Brain
• anatomy, biochemistry and personality
• Criticism
• of
• western thinking….not linked to the
• physical understanding
• of being human.
• Separation
• between mind and body.
• Variation
• in our biology's
• might
• be where the differences lie.
• Only
• in last 20 years
• has this been looked at more closely. …

Biology and Personality

• Does not represent one cohesive,, theoretical approach.
• Collection of approaches.
• These approaches seek out of origin of human personality and behaviour, looking for links between personality and biology.
• Three main areas:
• Evolutionary theory- personality
• dispositions arise from our evolutionary history and biological makeup
• (temperament) .
• Genetics and personality- how
• much of personality is genetically determined.
• Biological theories, brain anatomy and biochemistry- .personality
• dispositions are the product of a complex biological system.

Evolutionary theory and personality

• Provides theoretical platform that underlies human personality.
• Genotype: genetic makeup of individual. At birth, everyone starts with a unique
• genotype; some inbuilt instincts, a temperament and a pre-wired capacity to
• learn certain kinds of behaviours.
• Phenotype: an individual’s observable appearance and
• behaviour that arises out of the interaction of their genotype with the
• environment.
• Biological, environmental,
• behavioural and social shaping processes interact
• with the individual's genotype and create the unique psychological
• characteristics of the individual.
• Focus not on individuals but on patterns of behaviour common to all- 'human behaviour'
• Basic assumptions:
• certain behaviours exist due to evolutionary history of human species-helpful/necessary for survival
• the more a behaviour helps us survive and reproduce, more likely it is to occur in subsequent generations.
• Differences observed, can be understood a consequence of process of evolution throwing up personality variations- most adaptive of which survive and procreate.
• Different personalities may be adaptive in different ways.

Evolutionary theory and the five-factor model of personality

• David Buss- well known theorist (1991) - framework for understanding central concepts of (5 factor model) personality in three was:
• Providing understanding of major goals of humans,
• Describing psychological mechanisms and strategies that exist for reaching the goals and overcoming obstacles.
• Identifying individual differences in behaviours that humans use to reach such goals and to overcome obstacles to these goals.
• This model describes main dimensions of behaviour humans need to develop/adapt to environment, and to achieve their primary goals of survival and reproduction.
• This models has been investigated various species: including
• chimpanzees, cheetahs, hyenas, dogs, cats, pigs, guppies, octopuses and
• rhinoceros (Gosling & John, 1999; Gosling, 2001)
• Extraversion,
• neuroticism and agreeableness are found in most studies,
• Openness
• is found in the large minority of studies (chimpanzees exhibited openness and
• monkeys, hyenas and pigs showed curiosity).
• Conscientiousness is only found among chimpanzees.
• Core personality dimensions found amongst animals similar to five factor model (Gosling & John, 1999)

Evolutionary theory and personality

• Evolutionary theory provides useful framework/heuristic (set of rules and principles) which link effects of biology and environment
• to
• understand common variability (personality dimensions) in human behaviour
• (Buss, 1991).
• But....
• useful for explaining general personality traits, does not account for individual differences in behaviour.
• Many behavioural and personality
• phenomena may be the result of humans flexibly responding to circumstances,
• particularly the social structure, rather than evolutionary processes.
• Evolutionary theorists are speculating
• backwards across a number of generations. Such speculations cannot be directly
• empirically tested.
• Ideas about the nature and use of
• society’s goals to ensure the survival and reproduction of the species are
• difficult to test.

Genetics and personality

• Behavioural
• geneticists examine
• degree
• to which variation in the phenotype (observable traits of a
• person) can be attributed to variation in the genotype (underlying genetic
• structure) - ‘trait genetics’.
• Controversial - historical association
• with the eugenic movement and a more recent association with the idea of
• cloning.
• About
• 99% of human genes are identical from one individual to another. Behavioural
• genetics concentrates on the approximate 1% of genes that do vary.
• basic methodology
• is to compare similarities and differences in personality between populations
• of individuals who are and are not genetically related.
• Behavioural geneticists employ three
• primary research methods: family studies, studies, twin studies and adoption
• studies (Plomin,
• 2004).
• Basic
• assumption
• of behavioural genetics:
• personality traits
• are influenced by genes:
• -Traits more
• highly correlated across closer genetic relatives than across more distant
• genetic relatives.
• -Traits ought to be more highly correlated
• across pairs of identical monozygotic twins (MZ) who share 100% of their genes
• than across pairs of fraternal dizygotic twins (DZ) who share 50% of their
• genes.
• -Adoption studies – no genetic
• heritability between adoptive parents and their children.
• A
• statistic called the heritability coefficient is computed to reflect the
• genetic influence on traits.
• -Twin studies - heritability estimates for
• most personality traits are around 40-50%.
• -Non-twin studies/adoption studies -
• heritability estimates for most traits are around 20-30%.
• -Most
• likely explanation of difference
• is that effects
• of genes are interactive and multiplicative rather than additive.

Heritability of broad traits

• Numerous large twin studies
• taken place/ still taking
• place using data from twin registries in various countries.
• examples include:
• 12,898 adult twin pairs in Sweden (Floderus-Myrhed et al., 1980)
• 7,144 adult twin pairs in Finland (Rose
• et al., 1988)
• nompared DZ and MZ twins - evidence for a
• genetic component for extraversion-introversion (around 40-50%).
• Pederson et. al, (1988) also used a twin
• sample but included 95 MZ and 220 DZ twins reared apart. Also found strong
• genetic component for extraversion-introversion.
• Loehlin
• (1989) summarises results across studies for Eysenck’s measures of extraversion
• and neuroticism.

Heritability of the ‘Big Five’ and the ‘Big Three’ personality factors

• Several studies have compared the
• correlations between MZ twins and DZ twins for the five factor (e.g., Riemann
• et al., 1997) and three factor (e.g., Loehlin,
• 1989) models of personality.
• If MZ twins are more similar than
• DZ twins this is taken as evidence of heritability.
• ----Typically
• correlations between MZ twins for the five factors of personality are much
• larger than the correlations for DZ twins.
• ----Heritability
• estimates are derived by doubling the difference in correlations between MZ and
• DZ twins.

Folie 9

• 
• Bildunterschrift: Big varaiations, take one from other then multiply N.b. openess didn’t correalte with any part brain activity…
• 

Folie 10

• 
• Bildunterschrift: More studies, multiple genes involved
• Heritability estimates for the ‘Big Five’
• and the ‘Big Three’ personality factors
• -Overall, findings from many studies, twin and
• adoption, indicate:
• ---Personality influenced by genetic factors.
• ---There is a moderate heritability of
• personality from genetic factors, accounting for between 20 and 50 per cent of
• phenotypic variance (e.g., Saudino & Plomin (1996).
• ---Some studies indicate that genetic
• factors may explain as much as 40 – 50% of the variance in the main personality
• trait dimensions.
• Don’t
• know how it is linked but it is, the mind is an enigma still…

Genetics and personality