Genetics vs. Environment Their Role in Intelligence

Nature vs. Nurture in IQ “Is a person’s intelligence due more to genes or to environment?” Both genes & intelligence are crucial for any trait Environmental factors determines which genes get switched on. Example: nutrition affecting you reaching your genetic potential in height. Clearly, IQ is not the only psychological construct for which this debate applies, and instructors may wish to take a moment to name the other areas (i.e., personality, mental disorders, etc.) for which heritability is hotly debated.

Heredity and Environment Heritability Environment The variation within a group caused by genetic factors Thought to be about 50% Degree to which variation is due to environmental rather than genetic differences Environmental Factors can be early intervention, schooling and family life

Twin Studies & Family Influence Thomas Bouchard & the Minnesota Twins studies If trait genetic: closely related more similar than less closely related Many close relatives share environments too MSClip art Discussion here about the higher correlation between identical twins’ IQ scores than fraternal twins’ and whether siblings were reared together or apart and the genetic role then in intelligence

Twin Studies & Family Influence Thomas Bouchard & the Minnesota Twins studies Types of studies to separate effects monozygotic twins reared together monozygotic twins reared apart siblings/dizygotic reared together siblings/dizygotic reared apart adoptive siblings reared together MSClip art Discussion here about the higher correlation between identical twins’ IQ scores than fraternal twins’ and whether siblings were reared together or apart and the genetic role then in intelligence

Twin Studies figure scanned in from Gray's text, pg. 370, figure 10.7

Data Analysis-Genetic Factors The data show that both genetics and environment have an effect on IQ scores. The more closely two individuals are related genetically, the more similar their IQ scores: Identical twins reared together are more alike than are fraternal twins reared together.

Data Analysis-Environmental Factors Also show the importance of environmental influences: Identical twins reared together are more alike than are identical twins reared apart siblings who are reared together are more alike than are siblings reared in different homes.

Both genetics and environment have an effect on IQ scores

Adoption Studies Children's verbal ability scores became modestly more like their biological parents' scores. (Adapted from Plomin & DeFries, 1998.)

Group Differences in Intelligence Test Scores

Group Differences in Testing A number of studies show scoring differences between different racial, ethnic, and gender groups. Are these differences due to nature or to nurture? Studies suggest environment is playing a heavy role. Heredity and environment interact to produce intelligence in individuals.

Socioeconomic Differences A child’s ability is influenced by genetic factors and perhaps by the effects of the parents’ occupation and education on the home environment. Also, higher-income families may encourage a higher level of motivation to succeed.

Ethnic Differences There is variation in average IQ scores between ethnic groups, but MORE variation within groups. Research indicates that differences in IQ among ethnic groups may be due to differences in socioeconomic environment, parental education, nutrition, health care, and schools.

Why do Japanese and Chinese students perform better than Americans on intelligence and achievement tests? They score the same before school but once school starts they begin to show more gains. This due to: Spending more time in school More time doing homework Pressure and support from parents to achieve academically

Racial Difference in IQ Racial difference in average IQ among different racial groups can be measured More variation in IQ scores within a particular group than between groups

Racial Difference in IQ Stereotype Threat – When members of a particular group fear they are being thought of or evaluated according to a negative stereotype, fear that they may confirm the stereotype leading to self-doubt and anxiety resulting in poor performance.

Stereotype Threat—Race

Stereotype Threat—Gender

Effects of Discrimination on Intelligence The Burakumin people of Japan are severely discriminated against. Despite being genetically similar to Japanese people… Their IQ scores are 10 to 15 points lower than “normal” Japanese people.

Seed Analogy: Argument for Environment

Within and Between Group Differences Each corn field planted from same package of genetically diverse seeds One field is quite fertile, the other is not Within each field, differences due to genetics Between each field, differences due to environment (fertility) What can be concluded? Unless the environments of two racial groups are totally identical, it is impossible to estimate the overall genetic differences between the two groups.

Are IQ Tests Culturally Biased? Test will favor the people from the culture in which it was developed. Ex: If IQ test reflects white, middle-class cultural knowledge and values it could result in poor scores by minorities.

Are IQ Tests Culturally Biased? Factors like test-taking behavior, motivation, attitudes towards the test and previous experiences with tests can affect performance. Try some culturally biased tests yourself: Robert Williams IQ Test & the Dove Counterbalance Test Chitling Intelligence Test

Conditions that Can Raise IQ Scores

Conditions That Can Raise IQ Scores Enrichment programs such as Head Start can cause at least temporary gains in IQ scores. Spending time in projects such as Head Start may cause a child to be more motivated and have a better attitude toward school.