Ch.3 - Hereditary Influences on Behaviour

Question 1

What is ‘behavioural genetics’?

Answer 1

The scientific study of how genotype interacts with environment to determine behavioural attributes such as intelligence, personality, and mental health

Question 2

Are behavioural geneticists strict hereditarians?

Answer 2

No. They recognize that environmental variables also play a role in development.

Question 3

What are two approaches which behavioural geneticists use to assess hereditary contributions to behaviour?

Answer 3

Selective breeding and family studies

Question 4

What is ‘heritability’?

Answer 4

The amount of variability in a trait that is attributable to hereditary factors

Question 5

What is a ‘selective breeding experiment’?

Answer 5

A method of studying genetic influences by determining whether traits can be bred in animals through selective mating

Question 6

What is an example of a selective breeding experiment?

Answer 6

R.C. Tryon’s study suggested that maze-learning ability in rats is influenced by genetic makeup by selectively breeding ‘maze-bright’ rats and ‘maze-dull’ rats separately, and the difference in ability became greater

Question 7

Why does human behavioural genetics rely on family studies?

Answer 7

No genetic manipulation involved

Question 8

How does kinship relate to similarity?

Answer 8

Similarity between individuals who live in the same environment should increase as a function of their kinship

Question 9

Name two common types of family/kinship studies.

Answer 9

Twin design and adoption design

Question 10

What is a twin design/study?

Answer 10

Study in which sets of twins that differ in zygosity (kinship) are compared to determine the heritability of an attribute
“Are pairs of identical twins reared together more similar to each other on various attributes than pairs of fraternal twins reared together?”

Question 11

What would the result of a twin study look like if the genes affect the attribute(s) in question? Why?

Answer 11

Identical twins should be more similar, because they share 100% of genes (kinship = 1.00) whereas fraternal twins only share 50% (kinship = 0.50).

Question 12

What is the ‘adoption design’?

Answer 12

Study in which adoptees are compared with their biological relatives and their adoptive relatives to estimate the heritability of attribute(s)
“Are adopted children similar to their biological parents, whose genes they share (kinship = 0.50) or their adoptive parents, whose environment they share?”

Question 13

What would the result of an adoption design study look like if the genes affect the attribute(s) in question?

Answer 13

If adoptees resemble their biological parents in intelligence/personality, then genes must be influential in determining these attributes

Question 14

Give an example as to how family studies can also be used to estimate the extent to which various abilities/behaviours are influenced by the environment.

Answer 14

Consider genetically unrelated children adopted to same home. Their degree of kinship with each other and their adoptive parents is 0.00. If they resemble each other or their adoptive parents in any attributes, these likely are due to environmental factors.

Question 15

What is a ‘concordance rate’?

Answer 15

The percentage of cases in which a particular attribute is present for one member of a twin pair if it is present for the other. Only used for traits which an individual does or does not display entirely (e.g. drug habit or clinical depression)

Question 16

What do behavioural geneticists use to examine continuous traits that can assume many values (e.g. height and intelligence)?

Answer 16

Correlation coefficients

Question 17

What is a ‘heritability coefficient’? How is it calculated?

Answer 17

A numerical estimate, ranging from 0.00 to +1.00, of the amount of variation in an attribute that is attributable to hereditary factors.
H = (r identical twins - r fraternal twins) x 2

Question 18

What is a ‘nonshared environmental influence (NSE)’? How is its influence calculated?

Answer 18

An environmental influence that people living together do not share and that should make these individuals different from one another.
NSE = 1 - r (identical twins reared together)

Question 19

What is a ‘shared environmental influence (SE)’? How is its influence calculated?

Answer 19

An environmental influence that people living together share and that makes these individuals similar to one another.
SE = 1.00 - (H + NSE)

Question 20

Can heritability coefficients tell us if we have inherited a trait?

Answer 20

No. Heritability refers to the extent to which differences among individuals with that attribute are related to differences in genes that they have inherited.

Question 21

Can heritability coefficients be applied to individuals?

Answer 21

No.

Question 22

How can heritability estimates relate to a child’s capacity to change?

Answer 22

It does not. These estimates are based on a population, not individuals.

Question 23

How does the influence of genes on intellectual ability change as we age?

Answer 23

As children mature, genes appear to contribute more to individual differences in IQs

Question 24

What is introversion/extroversion?

Answer 24

The opposite poles of a personality dimension: introverts are shy, anxious around others, and tend to withdraw from social situations; extroverts are highly sociable and enjoy being with others

Question 25

What level of heritability does introversion/extroversion show?

Answer 25

Moderate level (similar to IQ)

Question 26

What is ‘empathic concern’?

Answer 26

A measure of the extent to which an individual recognizes the needs of others and is concerned about their welfare

Question 27

How heritable is ‘empathic concern’?

Answer 27

Reasonably heritable. Differences can be seen in identical vs. fraternal twins.

Question 28

Does the home environment have a significant contribution to personality?

Answer 28

No. Aspects of the home environment that all family members share does not appear to contribute much to the development of personality

Question 29

Which aspects of environment do behavioural geneticists believe contribute most to personality?

Answer 29

Nonshared environmental influences

Question 30

What are some examples of nonshared environmental influences in a home?

Answer 30

• Parents often treat sons differently than daughters
• Parents often treat first-born children differently than others
• Older sibling habitually dominates a younger sibling

Question 31

How did Denise Daniels and her associates measure nonshared environmental influences?

Answer 31

Ask adolescent siblings if they have been treated differently or experienced important differences

Question 32

How important of a contributor are nonshared environmental influences to personality?

Answer 32

Very important - at least as important as genes

Question 33

Which traits are shared environmental influences important for?

Answer 33

Moral, religious, social, and political interests/values

Question 34

What is ‘schizophrenia’?

Answer 34

A serious form of mental illness characterized by disturbances in logical thinking, emotional expression, and interpersonal behaviour

Question 35

What are indicators that schizophrenia is genetically influenced?

Answer 35

• Higher concordance rate for identical twins than fraternal twins
• Children with schizophrenic biological parent are more likely to be schizophrenic themselves (even if adopted early in life)

Question 36

What are some abnormal behaviours/conditions that are influenced by heredity?

Answer 36

Alcoholism, criminality, depression, hyperactivity, bipolar disorder, and a number of neurotic disorders

Question 37

What is ‘bipolar disorder’?

Answer 37

A psychological disorder characterized by extreme fluctuations in mood

Question 38

What is ‘neurotic disorder’?

Answer 38

An irrational pattern of thinking or behaviour that a person may use to contend with stress or to avoid anxiety

Question 39

What is a very important contributor to mental illnesses and behaviour disorders? How do you know?

Answer 39

Environment must be very important because identical twins are usually discordant/not alike

Question 40

Do individuals inherit behavioural disorders?

Answer 40

No - they inherit predispositions to develop certain illnesses/deviant patterns of behaviour. Usually takes many stressful experiences to trigger a mental illness

Question 41

What must we do to possibly prevent the onset of most genetically influenced disorders?

Answer 41

1 - Learn more about the environmental triggers that precipitate these disturbances while
2 - Striving to develop interventions/therapeutic techniques that will help high-risk individuals maintain emotional stability in the face of environmental stress

Question 42

What is ‘canalization’?

Answer 42

Genetic restriction of phenotype to a small number of developmental outcomes; a highly canalized attribute is one for which genes channel development along predetermined pathways, so that the environment has little effect on the phenotype that emerges

Question 43

Who coined the term ‘canalization’?

Answer 43

Conrad Waddington

Question 44

What is an example of a highly canalized human attribute?

Answer 44

Babbling in infancy

Question 45

What are some examples of potent environmental influences that can limit/canalize development?

Answer 45

• Gilbert Gottlieb found that duckling embryos exposed to chicken calls preferred chicken calls to that of their own mothers
• Early environments in which nutrition and social stimulation are inadequate can permanently stunt children’s growth and impair their intellectual development

Question 46

Name three things that the canalization principle illustrates.

Answer 46

1 - There are multiple pathways along which an individual might develop
2 - Nature and nurture combine to determine these pathways
3 - Either genes or environment may limit the extent to which the other factor can influence development

Question 47

What does Gottesman say about canalization?

Answer 47

Genes typically do not rigidly canalize behaviour. Instead, an individual genotype establishes a range of possible responses to different kinds of life experiences (‘range of reaction’).
Because people differ genetically, no two individuals should respond in the same way to any particular environment

Question 48

What is the ‘range-of-reaction principle’?

Answer 48

The idea that genotype sets limits on the range of possible phenotypes that a person might display in response to different environments

Question 49

What are three ways in which genes can influence the kinds of environments that we are likely to experience?
Who suggested these?

Answer 49

Passive Genotype/Environment Correlations, Evocative Genotype/Environment Correlations, and Active Genotype/Environment Correlations.
Scarr and McCartney

Question 50

Describe ‘Passive Genotype/Environment Correlations’?

Answer 50

The notion that the rearing environments that biological parents provide are influenced by the parents’ own genes, and hence are correlated with the child’s own genotype. E.g. athletic families

Question 51

Describe ‘Evocative Genotype/Environment Correlations’?

Answer 51

The notion that our heritable attributes affect others’ behaviour toward us and thus influence the social environment in which development takes place. E.g. smiley babies have more positive interactions

Question 52

Describe ‘Active Genotype/Environment Correlations’?

Answer 52

The notion that our genotypes affect the types of environments that we prefer and seek out. E.g. extrovert goes out

Question 53

How do Genotype/Environment Correlations influence development?

Answer 53

• Early on, Passive correlations are most significant (depend on parents)
• Active correlations exert more influence around school-age on
• Evocative correlations are always important

Question 54

What are the two reasons that identical twins bear a close behavioural resemblance throughout childhood/adolescence?

Answer 54

1 - Identical twins evoke similar reactions from other people
2 - Genotypes predispose them to prefer and select very similar environments