Intelligence: Heritability and Environment Flashcards
(21 cards)
Genotype
genetic constitution of an individual that matters, one can know about genotype by observing DNA
includes alleles (responsible for generating individual differences)
different from human genome which contains DNA coding for proteins and junk DNA
what is a gene
a region of the DNA strands that codes for proteins
who proposed genotype-phenotype distinction
Johannsen 1911
What are behavioural geneticists
look at relationship between genes, environment and behaviour
what is the phenotype
observed quality/outward manifestation of an organism. Influenced by genotype and environment
what is heritability
statistical measure that expresses a proportion of the observed variability in a trait that is a direct result of genetic variability
assessment of extent that phenotype is passed on from parents to children from genes
proportion of variance in a phenotype that is accounted for by variance in genes (VarG), expressed as a proportion of total variance in population (VarP)
H^2=varG/VarP
OR
H^2=VarG/VarG+VarE
changeability of heritability
example:
when those with phenylketonuria consume food with phenylalanine, it accumulates in their system and they increase risk of intellectual disability, seizures, behavioural problems, mental disorder - BUT treated with strict diet without phenylalanine
BUT if you reduce environmental variance, there is proportionally more genetic variance so higher heritability
Methods of Assessing Heritability
family studies/twin studies/adoption studies
Twin studies for intelligence
Riemann, Angleitna and Strelau (1997) show that correlation between monozygotic twins reared together for five factors of personality range from 0.42 to 0.56 whereas correlations between DZ twins are smaller and range from 0.13 to 0.35
similar to other research (twice the size)
what is the heritability estimate
heritability estimate (Falconers Formula) = ((correlation of MZ twins) - (corr of DZ twins)) x 2 expressed in percentages, so x200
how much of intelligence is genetics
intelligence is influenced by genetic factors - moderate heritability of personality from genetic factors, accounting between 20% and 50% of phenotypic variance
Adoption studies show children are more similar to their biological than adoptive parents in respect to personality
BUT children in same family turn out very different
Ridley et al = put together all family/twin/adoption studies showing IQ concordance rates AND Eysenck used this data to find estimation of heritability of intelligence as 69% - recent estimates are 40 to 80% (50% commonly accepted)
Polderman et al = 49% also average heritability estimated for all traits studied
Consistent findings from behaviour geneticists on general heritability
Plomin et al 2016
summarised top 10 findings from behaviour geneticists
psychological traits show significant and substantial genetic influence
no traits are 100% heritable
heritability is caused by many genes of small effects
phenotypic correlations between psychological traits show significant and substantial genetic mediation
heritability of intelligence increases through development
age-to-age stability is mainly due to genetics
most measures of environment show significant genetic influence
most associations between environmental measures and psychological traits are significantly mediated genetically
most environmental effects are not shared by children growing up in same family
abnormal is normal
shared versus non-shared
Polderman et al = meta-analysis showing 69% of traits influenced by environment are due to non-shared environments, not shared
Concordance rates of Intelligence
Ridley (1999) = put together all modern family, twins and adoption studies showing concordance rates of IQ for strangers and related people
Eysenck concluded from this data that estimation of intelligence heritability = 69% in general population
Recent estimates = 40-80% (50% commonly accepted)
Different Types of Genetic Variance
Additive genetic variance = genetic variation caused by individual’s genes inherited from parents
Dominant genetic variance = certain genes are expressed (dominant) and others aren’t (recessive)
Epistatic genetic variance = genes interact. certain inherited genes determine whether other genes we inherit will be expressed/supressed (process is called epistasis)
talking about only additive is called NARROW HERITABILITY
talking about all three types is BROAD HERITABILITY
Problems with Assessing Heritability
difficulty measuring dominant and epistatic genetic variance
no experimental control
families aren’t necessarily representative of normal population - ie twins are slightly less intelligent than non-twins maybe due to rivalry over nutrients in the womb AND adoptees are typically placed with stable families, reducing variance so inflating heritability estimates
Assortative mating can affect genetic variance and estimates of genetic heritability - people might mate with others similar to themselves (positive assortative mating) OR people completely different to themselves (negative assortative mating) - so increase and reduce range of variation/trait variance
some studies (Brace, 1996) show heritability varies across cultures
influences of intelligence
biological variables
family
school and education
culture
nutrition
Biological variables: Nutrition
Lynn nutrition and health care improvement are main factors responsible for Flynn effect (rapid rise in average IQ in most western countries in recent decades)
Malnutrition can impair brain function and IQ in the long-term (poor growth during infancy is negatively related to adolescent performance on cognitive and achievement tests)
iodine deficiency during pregnancy can lead to retardation (2 bil people affected by iodine deficiency, including 285 mil 6-12 year old children
40% of children aged 4 or under in developing countries have anaemia because of insufficient iron in diets)
longer breast-feeding is associated with higher verbal intelligence (2.3 to 6 IQ points of difference on a vocab intelligence between children)
vitamin-mineral supplements given to children were found to show increased non-verbal IQ scores (fluid intelligence)
fish oil supplement to pregnant and lactating mothers linked to increased cognitive ability
vitamin B12 and folate are important in cognitive function for old age
Flynn effect gains may be stronger among lower half of IQ distribution (supporting nutrition)
Biological variables: Lead and prenatal factors
negative correlation between environmental exposure to lead and mercury and children’s intelligence
prenatal factors
smoking and drinking during pregnancy is connected with health problems and brain damage of children - smoking 20 cigarettes per day or more during pregnancy was connected with worse IQ scores for children when 18-19 years old
BUT smoking and drinking also correlated with lower social class etc also and effects become lower when these other factors are controlled
most common condition with pregnant mum consuming alcohol is foetal alcohol syndrome where children are much smaller and have facial abnormalities and
Family Environment
shared and non-shared environments - twin and adoption studies suggest about 20% of individual differences in intelligence are due to non-shared environment
passive model = no nurture involved
child-effects model = genes make child intelligent, child makes parents talk intelligently to child
parents-effect model = genes make child intelligent and intelligent parents like talking to them so parents talk intelligently to it so intelligence raises even beyond what it would have been had genes alone been operating
social and economic status of family - correlation coefficient between 0.3 and 0.4
Gottfried meta-analysis to assess importance of many environmental factors in influencing children’s intelligence - best predictors of IQ scores were: provision of appropriate play materials, parental involvement and opportunities for variety in daily stimulation
educational intervention - IQ and academic performance intercorrelate about r=0.5 - children attending school regularly score higher on IQ tests
intervention called Heart Start in US (aimed at low-income children and their families) - programme worked in short-term, increasing IQ scores by a few points, but after a few years IQ gains are lost
birth order and family size - stemming from post-Freudian Adler - likely very small effects on intelligence and none on personality (Rohrer et al) - larger families contain children with lower intelligence than smaller families do - studies on first, second and third born find third-borns less smart but this may be because third-borns must come from larger families
why does birth order affect intelligence?
admixture hypothesis suggests something is mixed in with birth order that causes it ie lower SES
resource dilution model suggests, as more children join family, resources devoted to them by parents dwindle
confluence model suggests it is things like resource dilution or greater responsibility being assigned to first born or more exposure to parental language for first-born
parents are also older when they have later borns - sperms and eggs have accumulated more mutations (counter selective for IQ)
