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Genetics vs. EnvironmentTheir 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 traitEnvironmental factors determines which genes get switched on. Example: nutrition affecting you reaching your genetic potential in height.

+Heredity and Environment

The variation within a group caused by genetic factorsThought 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

Heritability Environment

+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

+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

+Twin Studies

+ Data Analysis-Genetic FactorsThe 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 StudiesChildren'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 T

est 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.