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Chapter 9

PSYA02H3 Chapter 9: Module 9.3 - Biological, Environmental, and Behavioural Influences on Intelligence (Textbook Notes)

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University of Toronto Scarborough
Steve Joordens

9.3 Biological, Environmental, and Behavioural Influences on Intelligence Biological Influences on Intelligence The Genetics of Intelligence: Twin and Adoption Studies o Studies of twins and adopted children allow researchers to estimate the genetic contribution to intelligence o The intelligence scores of identical twins correlate with each other at about 0.85 when they are raised in the same home, which is much higher than the correlation for fraternal twins The Heritability of Intelligence o The heritability of intelligence is estimated to be between 40 and 80 A heritability estimate describes how much of the differences between people in a sample can be accounted for by differences in their genes It means that a heritability estimate is not a single, fixed number; instead, it is a number that depends on the sample of people being studied Heritability estimates for different samples can be very different Behavioural Genomics o Intelligence scores can be attributed to genetic factors Behavioural genomics: Researchers use this technique to examines how specific genes interact with the environment to influence behaviours, including those related to intelligence Main focus of the behavioural genomics approach to intelligence is to identify genes that are related to cognitive abilities, such as learning and problem solving o Gene knockout (KO) studies: involve removing a specific gene and comparing the characteristics of animals with and without that gene Researchers discovered that removing one particular gene disrupted the ability of mice to learn spatial layouts o Transgenic animals: scientists insert genetic material into an animals genome (gene transplant) Environmental Influences on Intelligence Environmental conditions determine which genes get turned on for a given individual; thus, without the right circumstances, genes cant appropriately react the persons development Controlled experiments with animals show that growing up in physically and socially stimulating environments results in faster learning and enhanced brain development compared to growing up in a dull environment In this section, we review some of the major environmental factors that influence intelligence Birth Order o One highly debated environmental factors affecting intelligence is whether you were the oldest child in your family or whether you had older siblings A study of more than 240 000 people in Norway found that the IQs of first born children are about 3 points higher than those of second born children and 4 points higher than those of third born children Older siblings end up tutoring younger siblings, imparting the wisdom they have gained through experience on to their younger siblings Socioeconomic Status (SES)
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