Intelligence: Heredity and Environment in IQ

Intelligence The role of heredity and environment in IQ Dr Shue Ling Chong [email protected] 1 Today’s questions What is intelligence and how is it measured Is intelligence a single construct? Does intelligence depend on heredity or the environment?...

Intelligence The role of heredity and environment in IQ Dr Shue Ling Chong [email protected] 1 Today’s questions What is intelligence and how is it measured Is intelligence a single construct? Does intelligence depend on heredity or the environment? Can intelligence change over the life-span? 2 Background IQ = Intelligence Quotient is an index of an individual’s intelligence score IQ tests: Verbal, non-Verbal Advantages of non-verbal tests: eliminate issues with language, verbal abilities, cultural differences. 3 Background- Key figures and the history of intelligence Francis Galton : reasoned that intelligence is a product of natural selection, thus must be genetically determined. Saw potential in theory of evolution for planned human betterment. Binet & Simon: developed 1st IQ tests to measure student abilities for education purposes 4 Background- Key figures and the history of intelligence Lewis Terman and Maud Merrill Devised the Stanford-Binet Scale Studied a sample of “gifted” children throughout their lives (longitudinal study) Highly intelligent individuals not weaklings and misfits but healthy and stable 5 Background- Key figures and the history of intelligence Lewis Terman: Military use (Alpha, Beta test) to assign soldiers to tasks appropriate to their abilities during WW1. Eugenics: promote selective breeding to cultivate desirable characteristics (intellectually and physically) 6  Background- Key figures and the history of intelligence Cyril Burt Advised the British government to use aptitude tests to determine which children will go on to grammar schools (eleven plus). His research on intelligence seemed to suggest that occupational levels and social class are determined by innate and hereditary levels of intelligence. Problems with his data and analysis- fabricated? 7  Background- The History of Intelligence Other issues Cultural bias in test construction and standardization procedures. Intelligence tests favour groups from more affluent backgrounds and discriminate against less privileged racial, ethnic, or social groups. 8 Raven’s Progressive Matrices 9 10 More recent IQ tests WISC (Wechsler Intelligence Scale for children) WASI (Wechsler Adult Scale for Intelligence) Include verbal and non-verbal tests (tap into both crystalised and fluid intelligence). 11  Basic concepts Genotype= genetic make up of an organism Phenotype= refers to the observable physical properties of an organism; these include the organism's appearance, development, and behaviour. Phenotype includes both genotype and environmental influences. We can only measure phenotype. Performance depends on many factors. Degree of genetic relatedness= Looking at people with various degrees of relatedness can give us an understanding of the genetic basis of a concept. 12 Normal Distribution 67% 96% 13  Basic concepts Atheoretical definition of intelligence = intelligence is what IQ tests measure No theory of intelligence that will determine what questions should be included in an IQ test. However: IQ tests highly correlate with each other and with other measures (e.g. WM, Academic performance, problem solving, reasoning, career and income) Correlation = Statistical test and term that examines the relationship between 2 or more variables 14  Is intelligence a single construct? Generalised intelligence single construct that influences all cognitive functioning demonstrated through correlations of performances on different tests measures include: ◦ Stanford-Binet ◦ Raven’s Progressive Standard matrices 15  Or is intelligence a multiple construct? Composed of fluid and crystallized intelligence. (Cattell, 1987) Fluid intelligence: Cognitive functioning component not influenced by the environment, fixed throughout lifetime Crystalised intelligence: Stored factual information, benefits from schooling can change throughout life span Supported by correlations between tests of FI. and CI. respectively Both interact in some ways Relatively stable FI. but increasing CI. across life span 16  Is intelligence determined by genes or the environment? Twin studies: are valuable to examine genetic characteristics. However hard to separate genetic and environmental factors Degree of genetic relatedness: examining individuals with varying levels of shared genes can help us pick apart genetic influences 17  Bouchard & McGue (1981) Science, 212, 1055-1059 Kind of pairing Number of Pairs Correlation Identical twins reared 4,672.86 together Identical twins reared 65.72 apart Fraternal twins reared 5,546.60 together Non-twin siblings reared 26,473.47 together Non-twin siblings reared 203.24 apart Adopted children 369.34 (Genetically unrelated) 18  ENVIRONMENTAL FACTORS The environment in the womb (mother’s health and habits can influence fetus development) The Family Environment An enriched and stimulating environment correlates with IQ 19  Elardo et al (1975): The quality of the family environment  When speaking to the children, the mother’s voice conveys positive feeling  Mother structures the child’s play periods  Mother reads stories at least 3 times weekly  Family provides learning equipment appropriate to the age of the child  Child gets out of house at least 4 times a week  Mother shouts at child relatively infrequently  Mother spontaneously vocalizes to the child relatively frequently 20  Elardo et al (1975): The quality of the family environment Children were observed at 6 months and 24 months. They were tested (IQ) at 3 years and 4 1/2 years. Results: Rating of family when child was aged 24 months correlated with IQ at 3 years:.70 Rating of family when child was aged 6 months correlated with IQ at 4 1/2 years:.44 21  Important considerations Covariance between inheritance and environment Intelligent children tend to have intelligent parents who provide an enriched environment Transactional process Intelligent children provoke an intelligent response that potentially feeds their development even further It isn’t possible to specify which part of performance is due to heredity and which is due to the environment Estimates of heritability are based on population data and these don’t necessarily apply neatly to individual cases 22  Popular conceptions about IQ. Which one is supported by evidence? Taking vitamins can make you smarter (boost executive functions) Cognitive (brain) training can make you smarter (or increase cognitive abilities) 1st born children are smarter than their younger siblings SOME evidence for all HOWEVER only 1 of these statements is substantially supported by evidence 23  IQ Diet and nutrition Study by Benton and Roberts (1988), involving diet supplements Study with 6 year-old children 50% took a vitamin supplement every day for 3 months 50% took a placebo IQ measured before and after the study Children in the experimental group had a greater IQ increase compared to control 24  IQ Diet and nutrition Benton (2001). Increase in IQ scores was observed only in children with really poor nutrition. Children that have a healthy lifestyle and rich diet did not benefit Considerations Eysenck and Schoenthaler (1997). Metanalysis: hard to draw conclusions as different studies use different populations, vitamins, IQ tests etc. 25  IQ and cognitive training Cognitive training is a multimillion business…How effective is it? Owen et al. (2010) 11. 430 participants Five cognitive domains: Reasoning, Memory, Planning, Visuospatial skills and Attention 6-week training period Results: participants became better at the cognitive tasks they trained on but these effects did not transfer or generalise to other tasks and to everyday cognition 26  IQ and Birth order Number of siblings and birth order Single or 1st born children smarter than their younger siblings. Why? Take a minute to think why that may be. Think about this in relation to the Developmental theories we have introduced (Piaget and Vygotsky). 27  IQ and Birth order Confluence Model (Zajonc 1976) First born children spend more time with intelligent adults As the number of sibling increases, children spend more time with each other Interactions between children not as intellectually stimulating as between a child and adults 28  IQ and Birth order Dilution Model (Blake, 1981) – Parental finite resources First or alone child spends significant time with adults, gets more attention As the number of siblings increases the time parents spend with each child decreases. Less stimulating environment 29  The Flynn effect IQ maybe 25 points higher for a test designed in 1930s (even fluid intelligence) Can’t be evolutionary Improvements in education, nutrition and supportive parenting styles 30  Conclusions  Studies with identical twins suggest that intelligence is highly heritable, and this effect persists across the lifespan.  Because of the transactional process, it is difficult to know how genetic factors exert their influence.  Certain environmental factors influence intelligence and some of these might be non-obvious.  It’s important to recognize the role of environmental factors in IQ tests performance. Historically this has led to biases and discrimination. 31