Individual differences NATURE vs NURTURE and DEMOGRAPHICS

Assumptions made in twin and family studies

twin studies suggest personality is heritable

Trait Heritability Estimate

Extraversion 0.53

Neuroticism 0.41

Conscientiousness 0.44

Agreeableness 0.41

Openness 0.61

Jang, K.L., W.J. Livesley and P.A. Vernon (1996) Heritability of the Big Five personality dimensions and their facets. Journal of Personality 64: 577-91. 5

Twin and family studies that link heritability between MZ and DZ twins

• Heritability estimates in the range of 40% are common when resemblances between MZ twins is compared with resemblances between DZ twins (see also Johnson et al., 2008; van den Berg et al., 2014; Polderman et al., 2015; Vukasović and Bratko, 2015)

heritability estimates do not appear to vary by sex

heritability estimates and adoption studies

• Heritability estimates are typically slightly lower (~30%) in family/adoption studies where the resemblance between parent/biological child, or relatives separated by adoption, are compared (e.g. Bouchard and Loehlin, 2001; Rijsdijk and Sham, 2002)

what’s heritability

Heritability is a measure of how well differences in people’s genes account for differences in their traits.

Estimates of heritability

• Heritability denotes the proportion of variation in the characteristic that is associated with variation in genetic material.

• Heritability is a number between 0 and 1, like a correlation.

• Care needed when interpreting heritability estimates.

Candidate Gene Approach

• Late 1990s and early 2000s

• Hypothesis driven

• Constrained by prior knowledge

• Allows systematic scanning

Candidate genes approach: Extraversion

• Q: Variation in the DRD4 dopamine receptor gene associated with Novelty Seeking (≈ Extraversion)?

• It is a polymorphic gene (i.e. it occurs in several forms). This polymorphic region typically includes 2 to 11 repeats - 3 most common variants (DRD4 2R, DRD4 4R, DRD4 7R).

• DRD4 7R results in the expressed dopamine receptor having less affinity for dopamine binding.

• People with at least one 7-repeat allele have higher Novelty Seeking than other genotypes.

dopaimes’s D4 receptor gene variation- infidelity and sexual promiscuity

the wanderlust gene

candidate gene approach- neuroticsm and the serotonin transporter gene

Serotonin transporter gene (5- HTT) terminates the action of serotonin by facilitating its reuptake from the synapse.

• 5-HTTLPR: a polymorphism in the promoter region of the 5HTT gene.

• a 44bp deletion/insertion generated two alleles of 5- HTTLPR: Short (14-repeat) and Long (16-repeat).

• The short allele appears to be associated with decreased serotonergic function.

Candidate genes approach: Neuroticism genes related and conclusions

• Individuals with either one or two copies of the short 5- HTTLPR allele (so Short/Long or Short/Short) had higher Neuroticism scores that individuals homozygous for the long variant (Long/Long).

• Concluded that the 5-HTT polymorphism accounted for 3-4% of total variation (and 7-9% of inherited variance) in anxiety-related personality traits in individuals

The problem of non-replication

• By 2003, Munafo et al. identified 79 studies reporting associations between genes and personality traits.

• Most report at least one significant result, but results vary.

• Pooling the data, evidence is strongest for HTTLPR, some indications for DRD4.

• However, effects are small – a few percent of variance is explained; may also vary with sex and ethnicity.

• Hence, to reliably detect these associations you need thousands of participants.

• Even if they are real, the don’t explain much of the genetic basis of personality

Genome-Wide Association Studies (GWAS) Approach

• Instead of having a candidate gene in mind, you set markers across the whole genome.

• Should find all variants associated with phenotype of interest.

• Hypothesis-free

• Exploratory

• Lower power

• Large number of variants

GWAS and the problem of the missing heritability

• For personality, each GWAS finds some associations, but these initially explain <1% of the variance in personality, and usually did not replicate across studies.

• Problem of the missing heritability: Was described as “one of the great puzzles of current genetic research (Maher, 2008; Manolio et al., 2009)” (De Young and Clark, 2012).

have we overestimates heritability?

are identical twins really identical

were is the missing heritability

• We may have overestimated heritability?

• Multiple genes that all have a small effect (massive polygenicity):

• If scores of genes contribute to a given trait the single variant genes will only predict a very small amount of the variance in that trait. Essentially there may be many and multiple genes all predicting very small amounts of the variance.

• Gene-Gene interactions (GxG).

• Gene-Environment interactions (GxE).

correlation between depression and stressful life events

how frequency of an environmental exposure in a sample influences the ability to detect genetic effects and GxE interactions

epigenetic considerations

• The Epigenome (Epi = above) is a secondary layer of biochemical information that modify or mark the genome in a way that alters the instructions given by the DNA.

• Epigenetic factors, whilst not part of the DNA, impact on DNA and gene activation >> influence which genes are turned on and off at different times and places in the body.

• Whilst the genome remains largely static within an individual, the epigenome can be altered by the environment.

• Moreover, epigenetic changes can be passed from generation to generation via transgenerational epigenetic inheritance

Key points between genes and heritability

• There are candidate genes for involvement in personality variation, but their effects are small.

• GWAS studies had not found genetic basis of personality and raised the problem of the missing heritability.

• This is improving in recent years, and is aided by modern theoretical and methodological advances

• e.g. machine learning methods

• Massive polygenicity.

• G x G and G x E interactions/epigenetic factors may be important in personality.

Early experience and personality ”.

Childhood experience could explain variation in personality: Everyone agrees that heritability not 100%.

The statement above comes from measuring personality with broad, explicit self-rating scales; may not to be true with more specific or behavioural measures.

Belsky, Steinberg, and Draper’s (1991; Belsky 2012) theory of the development of reproductive strategies, also known as “psychosocial acceleration theory

The Belsky, Steinberg and Draper Hypothesis (1991)

• Individuals differ in sex and relationship behaviours, like fidelity, age at onset of sexual activity, sociosexuality, etc.

• What if early and promiscuous sexuality were an adaptive response to certain types of early experience?

• Unsupportive care from caregivers in first 5-7 years of life is a cue of harsh ecological conditions.

• Q: Does this cause a fast life history strategy (relative to peers who have experienced supportive care) as an adaptive response, to ensure reproductive fitness in an unpredictable/harsh environment.

what does Belsky, Steinberg and draper hypothesis predict?

>> A harsh development context is predicted to stimulate:

• earlier pubertal maturation and initiation of sexual activity,

• short-term and unstable pair-bonds, and

• limited parental investment as individuals sought to bear more children but not care for them intensively

evidence for Belsky, Steinberg and draper hypothesis and first pregnancy (Nettle et al, 2011)

(Nettle et al., 2011)

Prospective study of about 3000 women born in 1958.

Outcome was age at first pregnancy.

Predictors four measures of parental investment/stability in first 7 years of life: being breastfed, longest separation from mum, dad’s role, residential moves

. Belsky, Steinberg, Draper hypothesis predicts earlier first pregnancy the more adversities there are

RESULTS-

Menarche and sexual behaviour are different in girls from one-parent households

Childhood adversity and infidelity in adulthood (EPC: extra- pair copulations)

Retrospective Study (participants reflects on their childhoods to provide an estimate of early psychosocial stress).

natural experiments- periods and evacuees in Helsinki

Some children in Helsinki in 1940-4 were evacuated away from their families. It was effectively random who was evacuated and who not.

Puberty Prediction: Other findings

• Maltreated girls reached pubertal maturity 8 months earlier than non-maltreated girls (Costello et al., 2007).

• Harsh parenting at age 4.5 years predicted earlier menarche and, via this effect, indirectly fostered greater sexual risk-taking in adolescence (Belsky et al., 2007, 2010).

• Does not appear to apply to males (James et al., 2012).

Evidence of early experience on female behaviour and reproductive development in rhesus macaques

-Abusive birth mother, abusive rearing mother etc

-IV-abuse, mediator-responsiveness to stress, DV-infant handling

summary of the Belsky Steinberg draper hypothesis

The rationale and claims of the Belsky, Steinberg, Draper hypothesis.

Evidence supporting it (variety of human studies and an animal study that suggest that adopting a fast life reproductive strategy is at least partly link to early experience and not solely to genetic inheritance)

integrating the environmental and genetic architectures of aging and morality

combined environmental and genetic architectures of morality and age-related diseases

the puzzle of causality

-candidate genes are, at least, complete genes

-RBFOX1 is a RNA- binding protein that regulates splicing in neurons. It's been linked to a number of conditions, including Alzheimer's disease, autism spectrum disorders, bipolar disorder, and Tourette's syndrome

• Candidate genes are, at least, complete genes.

• SNPs are parts of genes, markers, modifiers, etc...

• But the basic mechanism of organismal biology requires genes

Fundamentals of “Evo Devo” biology

• We have about 20,000 genes that code for proteins.

• But there are (currently estimated) between 100,000 and over 1,000,000 unique types of protein.

• Alternative splicing

• ABCDE  ABD  ABCE

• Post-translational modification

• Protein folding

• Epigenetics

• ... and literally all of organismal biology

• Devolopment encompasses a lot of things!

• Deep homology

• Toolkit genes

• Internal regulatory networks

Developmental systems theory

• All biological processes operate by continually assembling new structures.

• Each such structure transcends the structures that made it. It will have its own systematic characteristics, information, functions and laws.

• Each such structure is nevertheless irreducible to any lower (or higher) level of structure, and can be described and explained only on its own terms.

• The major processes through which life as a whole operates, including evolution, heredity and the development of particular organisms, can only be accounted for by incorporating many more layers of structure and process than the conventional concepts of ‘gene’ and ‘environment’ normally allow for.

what does the Developmental systems theory mean for species

• A developmental system can be thought of as similar to “species”.

• So we are, each, developmental systems.

• Genetic effects are impossible to interpret outside of the developmental system.

• Genetics are inseparable from environment.

uncovering the complex genetics of human character

• Used a machine learning method for genome-wide association studies (GWAS) to uncover complex genotypic–phenotypic networks and environmental interactions.

• Identified “clusters of SNPs” within individuals.

• GxG interactions • Identified clusters of people with “distinct profiles of character traits”.

• Found 42 SNP sets that identified 727 gene loci and were significantly associated with one or more of the character profiles.

• “These gene sets modulate specific molecular processes in brain for intentional goal-setting, self-reflection, empathy, and episodic learning and memory.”

specific behaviours linked to behaviours

• “These gene sets modulate specific molecular processes in brain for intentional goal-setting, self-reflection, empathy, and episodic learning and memory.”

• Intentional goal setting

• Conscientiousness

• Self-reflection

• Neuroticism

• Empathy

• Agreeableness

• Episodic learning and memory

• Openness / intellect / IQ?

• Still missing ‘plasticity’ traits...

is character heredibility consistent across culture

• These appeared consistent across cultures and environments and explained nearly all the heritability expected for character in each sample (50 to 58%)

is personality heritability really missing?

“We postulate that personality heritability is not missing, but is distributed in multiple networks of interacting genetic and environmental variables that influence different people.”

what are the conclusions about nature and nurture

• Nature is at work.

• Nurture is at work.

• The balance depends on (particularl)

• ... what is being evaluated.

• ... what the circumstances are.

personality in retrospect

A demographic variable is

a characteristic such as age, gender, or race

• Can have impact on personality and/or cognitive measures

• Even though these would ideally not be influenced by these variables

• Many research participants are WEIRD: Western, Educated, Industrialized, Rich, and Democratic

• Also overrepresentation of WEIRD people clinically

Norming