BLOA 2.2

GENETICS AND

BEHAVIOUR

From Gene to Brain to Experience to Behavior

ENVIRONMENT

BEHAVIOURAL GENETICS – WHAT DOES THIS MEAN?

Humans share 93% of their genes with the rhesus macaque monkey and about 99% with rats – but what about the rest?

GENETICS AND ENVIRONMENT

THE CHALLENGE IS TO …

Discuss the extent to which genetics influence behaviour. Try and work out how much of a certain behaviour is inherited and how much is environmental.

? ?

WHAT IS INHERITED?

• Intelligence• Depression• Risk-taking

behaviour• Homosexuality• Problem solving

skills• Agoraphobia

Which of the

following do you

think might

be inherited? Why?

HUMAN CHARACTERISTICS WITH GENETIC COMPONENTS Physical: height, mass, obesity, voice

tone, blood pressure, tooth decay, athletic ability, age of death

Intellectual: memory, age of language acquisition, reading difficulties

Emotional/disorders: shyness, extroversion, emotionality, neuroticism, schizophrenia, anxiety, alcoholism

INTERACTION BETWEEN INHERITANCE AND ENVIRONMENT

Genetics (inherited)

Environment (experienced)

Behaviour

Diathesis-stress m

odel

THE DIATHESIS-STRESS MODEL Is used to explain the origin of depression This model argues that depression may

be a result of the interaction of a “genetic vulnerability” and traumatic environmental stimuli in early childhood.

Not everyone who experiences a traumatic childhood or has someone in the family who becomes depressed, will be depressed, therefore there in no single cause-and-effect relationship between genes and behaviour

GENETIC RESEARCH

Are in large extent based on correlational studies – twin studies, family studies and adoption studies.

CORRELATION STUDIES – WHO DO RESEARCHERS STUDY?

Twin studies

• MZ twins• DZ twins

Family studies

• (Grand)parents

• Siblings

Adoption

studies

• Adopted family

• Biological family

TECHNIQUESComparing Monozygotic

twins (MZ) with Dyzygotic twins (DZ). Since MZ twins have identical DNA, there

should be a higher concordance rate .

Comparing MZ twins reared together vs. MZ twins reared

apart. Why might this be better than the first

technique?

Using correlational research to establish a genetic argument for the origin of human behaviour

Twin studie

s

• Monozygotic (identical)

• Dizygotic (fraternal)

• Concordant trait• Both members of

a twin pair share a trait

• Discordant trait• A twin pair does

not share a trait

GENETIC RESEARCH Is to a large extent based on

correlational studiesWhat is that?

CORRELATIONCorrelations show the relationship between two variables. There is no manipulation of an IV, so cause and

effect are not established.

A correlation of +1.0 means as x increases, y increases. -1.0 means

that x increases, y decreases.

In twin research, we expect to find a higher correlational than when comparing a child to someone

outside of the family.

STRENGTHS OF TWIN STUDIES

Twin studies have produced a great deal of data in support of biological roots of disorders; this has helped psychologists to stress prevention for those who are vulnerable to such disorders.

There is a high cross-cultural reliability of concordance levels.

LIMITATIONS OF TWIN STUDIES MZ twins are rarely separated at birth

and raised in a totally different environment, yet this is really necessary to substantiate claims. MZ twins reared together share many of the same experiences. DZ twins reared together may not share the same experiences due to levels of attractiveness or temperament.

ADOPTION STUDIES

Adoption studies tend to compare the adopted child with the biological mother and the adoptive mother to determine which has the higher concordance rate for a given behaviour.Why might adoption studies at times be preferrable to twin studies?

STRENGTHS OF ADOPTION STUDIES

Adoption studies allow researchers to isolate variables. If a biological mother has no contact since birth and still matches for a specific trait - for example, the adopted child’s IQ is better than the adoptive mother and in concordance with the birth mother - this is strong evidence that genes play a significant role in the development of this trait.

LIMITATIONS OF ADOPTION STUDIES Selective placement is a problem.

Babies tend to placed with families similar in background to the natural parents.

Adopted children – as well as twins - are not representative of all children.

The act of being given up for adoption may affect the child’s behaviour.

FAMILY STUDIES A more representative sample of the

general population. A child inherits half of its genes from the

father and half from the mother Sibling will share 50% with each other Grandparents will share 25% with their

grandparents First cousins will share 12,5% with each

other

FAMILY STUDIES These different degrees of genetic

relatedness are compared with behaviour.

For example: if one study intelligence and believe that IQ has a lot to do with the genes, there should be a strong correlation in IQ between children and their mother and fathers, but a weak

correlation in IQ with their second cousins and if any with strangers

WHAT IS INTELLIGENCE?

SO, what did you get on your SATs? Jane said she got a 2350…that means she’s

really smart, right?Does it?

Is it the ability to use reason and logic? Is it the ability to write and speak clearly? Is it limited to one’s performance in school? Is it behavior in social situations? How about knowing when you’re wrong?

Not that simple, right?

There are many psychological theories about intelligence

INTELLIGENT RESEARCH

• Beginning of 20th century – a great interest in the role of genetics and behaviour

• Alfred Binnet – developed first intelligence test in order to improve the French education system

• Is intelligence inherited or is it the result of environmental stimuli?

Central argument is that human intelligence is substantially Influenced by both inherited and environmental factors andis a better predictor of many Personal dynamics, including financial income, job performance, chance ofunwanted pregnancy, and involvement in crime than are an individual's parental socioeconomic status, or education level. 

Give me a dozen healthy infants, and my own

specified world to bring them up in and I'll

guarantee to take any one at random and train him

to become any type of specialist I might select –

doctor, lawyer, artist, merchant-chief and, yes, even

beggar-man and thief, regardless of his talents,

penchants, tendencies, abilities, vocations, and race

of his ancestors.

John B. Watson

INTELLIGENCE – ONGOING DEBATE What is it? How can it be measured? Charles Spearman – theorized that there

is a general intelligence factor, which he called the “g” factor.

Modern intelligence testing attempts to assess this “g”

But the question is: where does “g” come from?

CHARLES SPEARMAN “G” FACTOR

Spearman defined ‘g’ as: “the innate ability to perceive relationships and educe co-relationships”

Don’t test facts and subject knowledge Test spatial ability, reasoning, divergent thinking, and verbal fluency

TEST BIAS?Tests do discriminate.

But some argue that there sole purpose is to discriminate.

We have to look at the type of discrimination.

GENETIC AND ENVIRONMENTAL INFLUENCES ON INTELLIGENCE

No other topic in psychology is so passionately followed as the one that asks

the question, “Is intelligence due to genetics or environment?”

RESEARCH ON INTELLIGENCE Bouchard and McGue (1981) reviewed

111 studies of IQ correlations between siblings

It was META-ANALYSIS (statistical synthesis of the data from a set of comparable studies)

Results: the closer the kinship, the higher the correlation for IQ

MINNESOTA TWIN STUDYBOUCHARD ET AL. 1990

• Aim of the study: researchers seek to identify the genetic and environmental influences on the development of psychological traits.

• Longitudinal study of 11-17 year-old twins, started in 1979. Involved a week-long of medical and psychological assessment of identical and fraternal twins separated in early life.

• This is the most cross-cultural stydy with participants from all over the world.

METHOD & COLLECTING DATA• Medical Assessment:

- Psychiatric interview- Medical life history- Standard blood test- Detailed dental & periodontal exams

• Psychological Assessment:-Academic ability-Personality & Interests-Family & Social relationships-Mental & Physical health-Psychological Measurements

50 hours of testing and

interviews

CONCORDANCE RATES OF INTELIGENCE

Same person tested twice 87%

Identical tins reared together 86%

Identical twins reared apart 76%Fraternal twins reared together 55%

Biological siblings reared together 47%

Researchers determined a heritability estimate of 70% - that is 70% intelligence can be attributed to genetic inheritance

FINDINGS (EXAMPLES)Separated as infants, twins Gerald (Jerry Levey) and Mark Newman grew up to share characteristics ranging from their firefighting avocation to taste in beer.• Neither of them knew of the others existence• When they first met, they saw their reflection in the other

person.• Grew same mustache, wore the same glasses.• Both worked in supermarkets for a while.• Both volunteer fire fighters.• Both men are bachelors and are attracted to the same kind of women.• Both brought up in the Jewish faith but neither is particularly religious.• Both men drink only Budweiser Beer. ( They even hold the can in the

same way• Quote - “we kept making the same remarks at the same time and

using the same gestures. It was spooky...He is he and I am I, and we are one.”

MINNESOTA TWIN STUDY (BOUCHARD ET AL. 1990)• Pros:– Mean age was 41 years old (most twin studies

are about adolescents)– Most cross-cultural study to date

• Cons:– Ethical concerns in reunited twins– Equal environment assumption (just because

twins lived together doesn’t mean they had the same experiences growing up)

– Used media coverage to recruit participants– Frequency of contact between twins prior to

study could not be controlled

THE BOUCHARD STUDY SUFFERS FROM THE EQUAL ENVIRONMENT FALLACY

The Bouchard study suffers from the equal environment fallacy –

a parent preferred one twin over the other,

they were in different classes in school, they have different peer groups based

on extracurricular interests.

BUT…..(AND THAT’S A BIG “BUT”)

“Twin research is flawed, provocative, and fascinating, and it topples some of our most cherished notions…such as our beliefs that parenting styles make an irrevocable difference, that we can mould our children, that we are free agents piecing together our destinies.”

From Roderick Angle’s “Nature’s Clone” in Psychology today, July 1, 1997

MINNESOTA TWIN STUDYAlthough the original longitudinal study is now finished, the Minnesota Center for Twin & Family Research is still conducting studies.See https://mctfr.psych.umn.edu/aboutus/index.html for updates.

ADOPTION STUDY Wahlstein (1997) – well- controlled adoption

studies in France He found that transfering an infant from a

family with low socio – economic status to a home where parents have a high socio – economic status improved childhood IQ

scores by 12-16 points

ADOPTION STUDIES• Scarr and Weinberg (1977) & Horn et al.

(1979)• Studied parents with both biological and

adopted children• So same environment – any differences should

be due to… what?

– Same upbringing and environment, but different biology

– Parents were white and middle class– Children were from lower-class with low-IQ biological

parents• No significant difference in IQ correlations

GENETIC INFLUENCESStudies of twins, family members, and

adopted children together support the idea that there is a significant genetic

contribution to intelligence.

HERITABILITY IN IQ LEVELS

Plomin and Petrill (1997) Correlations between parents and child IQs

change over time It is possible that our genetic disposition

pushes us towards environments that accentuate that disposition, thus leading to increased heritability throughout the lifespan

Socio-economic class is an important environmental factor (i.e. poverty)

HAINER ET AL. (1988)

PET Scan Individuals with high IQ had a lower

metabolic rate when solving a reasoning problem

No change in metabolic rate with a data recall problem

Higher IQs use less energy to think Called the less effort hypothesis

FLYNN EFFECTIn the past 60 years, intelligence scores have risen steadily by an average of 27

points. This phenomenon is known as the Flynn effect.

AVERAGE MEAN SCORES ON STANDARD IQ TESTS GO UP BY ABOUT 3 POINTS EVERY DECADE

Better at cracking the test? Real increase in intelligence? Better nutrition, schooling, childhoods,

technology?

PSYCHOLOGY Evolutionary explanation of

behaviour

EVOLUTIONARY PSYCHOLOGY Is determined on one idea that as genes

mutate, those that are advantageous are passed down through a process of natural selection.

Natural selection cannot select for a behaviour.-can only select mechanisms that produce behaviour

CHARLES DARWIN “FATHER OF THE EVOLUTIONARY THEORY” Theory of natural

selection

Animals-evolution Primates- insight into

human behaviour

Mate selection Love of mother Self-preservation

PROFESSOR TETSURO MATSUZAWA 2007

Study challenges the belief of many people, including a number of scientists, that "humans are superior to chimpanzees in all cognitive functions," said researcher Tetsuro Matsuzawa of Kyoto University.Video: http://news.nationalgeographic.com/news/2007/12/071204-chimps-video-ap.html

One memory test included three five-year-old chimps who were taught the order of Arabic numerals 1 through 9, and a dozen human volunteers.

FESSLER (2006) / DISGUST Study of emotions Dan Fessler (USC) Disgust-enabled ancestors to survive long

enough to produce offspring, who in turn passed the same sensitivities to us.

Nausea experienced by pregnant women (1st trimester)4c xz

FESSLER CONT. Fessler hypothesized that the nausea

response helps to compensate for the suppressed immune system.

Fessler gathered 496 healthy pregnant women(ages 18-50) to rank how disgusting they found 32 disgusting scenarios

• Walking barefoot and stepping on earthworm

• Sticking fish hook through their finger • Maggots on a piece of meant in an

outdoor waste bin

BEFORE EXPERIMENT Fessler asked questions to help determine

whether they were experiencing morning sickness.

First trimester scored the highest

More effective when involving food Food-borne The sensitivity lowers the risk of disease

and infection decreases in consistent with the view of disgust as a form of protection against disease.

CURTIS ET AL. (2004) Patterns in disgust responses Online survey; 20 images Level of disgust? 7 pairs in which one was infectious or

potentially harmful to the immune system vs. non-infectuous

77,000 participants from 165 countries Findings affirmed that most disgusted when

could affect us Supports idea that disgust is a key to

successful reproduction

The original survey can be found at www.bbc.co.uk/sciencehurnanbody/mind/surveys/disgust

THINGS TO CONSIDER…

Difificult to test empirically some evolution-based therefore researchers may be forced to be bias when making affirmations.

Little is known about the behaviour of early Homo sapiens, so statements about humans “used to be” are hypothetical

Evolutionary arguments often underestimate the role of cultural influences in shaping behaviour

ETHICAL CONSIDERATIONS; GENETIC HERITAGE AND PEOPLE’S LIFE.

One may not like to share about their past

Affected to find out things they didn’t want to know about their ancestors

Confidentiality and privacy

SO GENES ARE THE CAUSE OF OUR BEAHVIOUR?

Not exactly!!

It allows us to trace back our actions and their motives.

Genes can take the blame ;)

CRITICAL THINKING ABOUT BEHAVIOURAL GENETICS Selective placement: adoption agencies try and place children

in families that are similar to their own. Therefore the environment for a twin raised in an adoptive family and a twin raised in the biological family may be very similar. This is the same with adopted children, when compared with their biological and adoptive parents – the environmental factor is difficult to determine. (See p 28-29 of the Psychology e-text)

Twin studies: even if raised apart, identical twins have common age, common sex, similar appearance, similar socioeconomic and cultural environment (usually, see above), and a common prenatal environment.

Increasing heritability: correlations between parent and child IQs change over time, becoming stronger as the child ages. (See Plomin and Petrill, 1997, p 56 in your Course Companion). What could this mean?

In the Course Companion it is stated that “poverty - not genetic inferiority – is key to understanding differences in intelligence” (p56). What could this mean?

WANT TO TEST YOUR OWN IQ? (AND DEVELOP YOUR CRITICAL THINKING).Here are 3 links to online IQ tests. Try and take all 3 tests in the same day. Ignore the results, except to compare them. If they are different, how do you explain this? Have you become more/less intelligent in just one day? If they are the same, is this sufficient to say that you have this “IQ”?http://www.free-iqtest.net/ www.learnmyself.com http://www.iqleague.com (Note that these are all free. The second asks for your email address, but you can make one up).