L4 AB

Personality

Nature

•       Francis Galton (1822 –1911)

•       Hereditary Genius (1869)

•       Coined term "nature versus nurture“

•       … where every lad had a chance of showing his abilities, and, if highly gifted, was enabled to achieve a first-class education and entrance into professional life…

Nurture

•       JB Watson (1878 – 1958)

•       Psychology as the Behaviorist Views it (1913)

•       “Little Albert" experiment

•       “Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select – doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors”

(Behaviorism, 1930, p. 82)

Present Day

•       most agree that individual differences develop as a result of interaction  between environment & genetics

•       Can be discussed and analysed separately but do not operate independently

•       Where scientists still disagree, is the relative contribution

Assessing Heritability

•       Estimates of extent to which variation in scores on measures of interest is due to genetic factors

•       Proportion of shared variance between individuals - %

•       Heritability coefficient (h²) – between 0 and 1

Twin Studies methodology

•       MZ (monozygotic) twins: develop from same fertilised egg & are genetically identical

•       DZ (dizygotic) fraternal twins: develop from separate eggs & are as genetically similar as any other siblings - @ 50% genes

•       Research assumptions:

•       MZ genetically identical: differences are environmental

•       DZ differ genetically: if same environment, differences must be genetic

Twin Concordance

•       Concordance: presence of a given trait in both individuals in twin pair

•       Diane Arbus (Identical twins, Roselle, N.J. 1967)

•       Even when people look the same, their personalities may be different.

Rates for big 5

•       Jang et al (2002): MZ (N = 253) & DZ (N = 207) twins from Canada & MZ (526) & DZ (269) twins from Germany completed NEO-PI (Big 5):

So..

•       Jang et al suggest only @40-50% concordance even for MZ reared together in same family

•       Assumptions reflect ideal conditions for research: rarely met

•       Assume a shared environment: the only difference between MZ & DZ twins brought up together is genetic

Environmental Factors that differentially affect even MZ twins?

•       Friends

•       Relationships

•       Trauma

•       Social influences

•       Personal experiences

Same or different environment?

•       Shared genes do not guarantee shared experiences

•       Unique experience of each child must be considered (perception)

•       Even when twins together live together and with biological parents & siblings:

•        

Unshared environment

•       “Experiences in the family do not make siblings similar.  The only factors important to children‘s development are those that are experienced differently by children in the same family… in other words, environmental influences that affect development operate on an individual-by-individual basis, not on a family-by-family basis… what runs in families is DNA, not shared experience in the family. “

•       Dunn & Plomin (1990, p. 42-43), Also Plomin (2011)

•       Differences that siblings may experience

•       Sex

•       Birth order

•       Life events particular to child (e.g. illness)

•       Peer group experiences

•       Personality characteristics……

•       Differential parenting

•       MZ twins: parents may try to treat differently

•       DZ twins: may not experience exactly the same environment

•       Reiss, et al (e.g. 2005): differential parenting, interaction between genetics of child and of parent

Adoption Studies

•       MZ Twins raised apart: Identical genes/differing environments

•       Compare children, biological & adoptive parents

•       Between biological & adoptive environments

•       Families with both adopted & biological children

•       Are biological children similar/different to adopted siblings?

•       Which are more similar to parents?

•       Fewer adoption studies, smaller numbers of participants

•       Suggest less genetic influence than twin studies: e.g. Plomin & Caspi (1999) estimate:

•       Biological parents/children: 0.16 for E and 0.13 for N

•       Adoptive parents/children: 0.01 for E and 0.05 for N

•       Is H² overestimated in twin studies – or does adoption restrict measurement of environmental influences?

•       Children are often adopted by extended family

•       Or, by similar to birth families

•       Placement strategy of agencies

Jim Twins

•       Jim Lewis and Jim Springer

•       raised apart from age of 4 weeks.

•       reunited at the age of 39 in 1979

•       tension headaches,

•       nail biting,

•       smoked Salem cigarettes,

•       drove the same type of car

•       vacationed same beach in Florida.

•       childhood dogs named “Toy.”

•       married twice — Linda then Betty

Limitations of twin studies

•       How representative are twins of general population?

•       Placental & birth experiences

•       Runs in families

•       Older mothers (multiple eggs; IVF)

•       MZs closer to each other as children & as adults

•       Unshared environment

•       Some genes may not have 100% penetrance: different consequences in genetically identical individuals

•       Trait/characteristic may be polygenic, i.e. caused by more than one gene

So is personality inherited ?

•       Heritability studies with twins suggest interaction between genes & environment

•       Genetic component

•       Environmental triggers

•       Limitations

•       Are twins typical?

•       Controllability of environmental factors

•       Unshared environment

•       A final question - Does it matter?

Assortive mating

•       Couples tend to have traits in common

•       Do not mate with random people: Assortative mating

•       Key issue is we are selective

•       Typical relationship between partners IQ;

•        r = .40,

•       compared to @ r = .20 for weight, colour, personality.

•       Higher IQ parents have higher intelligence kids

•       Lower IQ parents tend to have more children

Family size and birth order

•       Belmont & Marolla (1973): larger family size – lower IQ (RPM) even when SES controlled for

•       First born (FB): IQ > than later born (LB)

•       Interaction with overall family size (effect strongest on larger families)

1. Admixture: Lower SES & IQ tend to have more children (e.g. Rodgers, 2001)

2. Resource dilution: Resources (time, energy, cash) are finite and diminish with number of children (e.g. Downey, 2001), FB gets 100% to begin with, SB gets 50%, TB only 33%

3.        Confluence: Intellectual development occurs within family context and this changes over time (e.g. Zajonc, 2001)

•       FB have time with 100% parental attention

•       Additional children limits attention paid to all

•       Older children may have to care for younger ones, take the lead, explain things to them

•       FB exposed to more adult language and ideas. LB hear speech from other children as well as parents

•       National Longitudinal Survey of youth (Rogers et al 2000)

•       US study of >11,000, age 14-22 years, and children born to them

o   No relationship family size and intelligence

•       Methodological debate – still ongoing

o   Much work has compared within families

o   NLYS between families – other factors may determine differences

                  (Michalski & Shackelford, 2001)

MZ separated at age 2

•       Born in Seoul, South Korea, in 1974

•       Separated at age 2 after one of them got lost at a market and was eventually adopted by American parents.

•       Reunited in 2020 (aged 36)

•       Twin in Korea described loving and harmonious home, while the one who lived in the U.S. regular conflict and the eventual divorce of her adoptive parents.

Personality:

•       US = individualist/SK = more collectivist values

•       Mental health and self-esteem the same

•       Both high on Conscientiousness - purposeful, well-organized, dutiful, and achievement-striving

Intelligence

•       SK twin 16 points higher than US twin (US: 84, SK: 100)

•       WAIS

•       Ravens matrices

•        

The bell curve controversy

Richard Herrnstein & Charles Murray (1994). The Bell Curve: intelligence and class structure in American life.

IQ will become the basis of class system – cognitive elite

•       US education/workplace dumbed down by lower IQ

•       Talented not reaching potential

•       No recommendations to improve intelligence/affirmative action

•       Instead – accept inequality

•       Resources go to supporting talented, rather than disadvantaged

However

•       Intelligence considered hierarchy of abilities, not just gf

•       May not be captured in IQ tests

•       IQ is heritable, but not completely.

•       Variance within population about 10 times greater than between races

•       Within race, no genes that all members have in common

Social Class

•       SES and IQ: estimates between r = .3 and r = .5 (higher SES-higher IQ)

•       45 IQ points between classes 1 and 5 (3 SD)

•       10 point even when SE factors controlled for (e.g. Mackintosh, 1998 based on UK longitudinal data)

Is socio-economic status (SES) determined by individual differences in IQ, or the cause of them?

•       Adoption studies:

•       Capron & Duyme (1989). IQ at age 14

•       Kendler et al (2015) adoptees raised apart:

•       similar results

•       Full and half-siblings

Gene x environment interaction effect on IQ

•       SES associated with differences in:

•       executive function, memory, emotional regulation and underlying brain areas

•       But variance is also accounted for by genetics

•       Inherited biological and psychological factors

•       Genetics cause SES differences through lowered educational and occupational performance

•       Interventions cannot change gf, but may support cognitive development

•       Lots of debate and controversy

•       Social policy based on assumption that ID are largely due to environmental factors

•       cycles of poverty, deprivation continue unless social intervention

•       We have a responsibility to intervene

•       Summary

•       Genetic heritability (partially)

•       Interaction with social factors

•       Birth order, family size and SES…..

•       Differences in IQ between ethnic groups exist, but social/cultural rather than genetic

Introduction to Nature-Nurture Debate

• Nature vs. Nurture: Investigates the extent to which genetics (nature) or environment (nurture) influences personality and intelligence.

• No categorical answers; evidence helps to make informed judgments.

• Emphasis on the significance of reading beyond lecture materials for exam preparation.

Key Themes of the Lecture

• Review of Previous Lectures: Discussion of personality traits, their stability, and intelligence.

• Focus on understanding nature-nurture interactions in shaping personality and intelligence.

Vote on Nature vs. Nurture

• Conducted a student vote on perceived influences on personality: genetics or environment.

• Majority favored environmental factors over genetics, aligning with previous cohort responses.

Historical Context of the Debate

• Francis Galton (1869): Coined the term "nature vs. nurture." Argued for genetic influences on intelligence; believed everyone had potential if given the right opportunities.

• J.B. Watson: Advocated for environmental influences on personality through experiments like Little Albert, demonstrating conditioning of fears.

Current Understanding

• Gene-Environment Interaction: Most psychologists agree on an interaction model, where genetic predispositions manifest through environmental triggers.

• Disagreement persists over the relative contributions of genetics vs. environment.

Heritability

• Definition: Heritability estimates the extent to which variation in a trait (like intelligence) is due to genetic factors.

• Expressed in percentage or coefficients (0-1 scale).

• Example estimates:

  • Height: 0.8 (80% genetic influence)

  • IQ: 0.4 (40% genetic influence)

  • Big Five Personality Traits: ranging around 0.4 to 0.5.

Twin and Adoption Studies

• Importance: Used to parse out genetic vs. environmental influences on personality and intelligence.

• Types of Twins:

  • Monozygotic (MZ) Twins: Genetically identical. Differences suggest environmental influences.

  • Dizygotic (DZ) Twins: Share about 50% of genes; differences can suggest genetic contributions.

• Concordance Rates: Reflect similarities in traits between twins, highlighting genetic influences.

Findings on the Big Five Personality Traits

• Studies show heritability coefficients for the Big Five traits:

  • Openness: 0.46

  • Other traits similar in heritability.

• Significant environmental factors remain unexplained in personality variance.

Limitations of Twin Studies

• Twin studies often assume shared environments, which may not reflect real-life experiences.

• Unshared Environments: Individual experiences within the same family significantly affect personality development.

Adoption Studies

• Complexity of environmental influences in adopted children; isolating genetic factors becomes challenging.

• Example of the Jim Twins: Raised apart yet exhibited converging life patterns, indicating strong hereditary influences despite different environments.

Bell Curve Controversy

• Herrnstein and Murray's "The Bell Curve":

  • Controversial arguments regarding IQ disparities among races and socio-economic classes.

  • Lack of nuance around the complexities of intelligence and the role of social factors.

Socioeconomic Status (SES) and IQ

• Studies suggest a correlation between SES and cognitive abilities, reinforcing the idea of interaction.

• Higher parental intelligence and better SES often correlate with higher child IQs.

• Potential Interventions: Nutritional support and educational interventions can help mitigate the effects of low SES on children's cognitive development.

Conclusion

• Intelligence and personality are influenced by an interplay of genetic and environmental factors.

• Discussions continue around social policies and interventions aimed at educational equity based on these understandings.