Investigating the genetic basis of behaviour

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Investigating the genetic basis of behaviour

  • Lesson 1 Objectives
  • To know the difference between nature and nurture
  • To know the terms genotype and phenotype
  • To understand why psychologists debate genetic influences on behaviour

Nature or Nurture?

  • Watch this

Nature Nurture

  • Influences that occur outside the individual could be
  • Pre-natal environment
  • Diet
  • Pollution
  • Family/peers
  • Media

The Current view

  • It is impossible to view human characteristics and behaviour as purely biological or environmental
  • Each individual human has a genotype – this is the genetic composition
  • Each person has a phenotype which is what the individual becomes when their genes interact with the environment.

Why is it a debate?

  • It isn’t really because there is wide acceptance that genes and the environment interact.
  • Our environment can affect our genes
  • Genes can affect our environment
  • Psychologists disagree over the extent of genetic vs environmental influences e.g they may agree that IQ is down to both genes and environment but they disagree on how much of it genes and how much is environment.
  • ESSAY TIP 1 – Controversial Question
  • How much of behaviour is determined by genes and how much by environment?

Why is this a big question?

  • A belief that intelligence is genetic could lead to practice of eugenics – selective breeding of humans.
  • Likewise a belief that behaviour is purely down to environment may lead to harsh regimes based on conditioning people.
  • See textbook for examples!

The Application of Psychological knowledge

  • If we think a behaviour is mostly genetic, we would treat it differently than if we thought it was environmental (or learned)
  • For example think about….
  • Intelligence
  • Criminality
  • Homosexuality


  • Complete gap fill and questions 1-3 on your handout.

Objectives Lesson 2

The Role of Genes in Human Behaviour

  • NO – I said GENES

Twin Studies, adoption studies and correlation

  • How they contribute to our understanding of the debate

Twin and adoption studies look to see how much of our INDIVIDUAL DIFFERENCES are due to genes

  • For example they want to know the reason why I like oranges and you don’t. Is it more nature than nurture or vice versa.
  • The extent to which this DIFFERENCE is due to genetic make-up is called a
  • Heritability Estimate.


  • When we say we compare twins or children with parents we mean on a measurable variable and because we are psychologists this will be something to do with behaviour for example
  • Intelligence
  • Aggression
  • Introversion/extroversion
  • Sense of humour
  • Mental illnesses such as depression or schizophrenia
  • Whatever it is you need some kind of test to give both parties that will give a number representing a behaviour

Twin studies

  • With twin studies there are 2 methods
  • 1.comparing Monozygotic twins with Dyzygotic twins
  • Eg
  • MZ 0.86
  • DZ 0.46
  • What does this indicate? .
  • 2.Comparing Monozygotic twins reared together with monozygotic twins reared apart
  • Eg
  • Together 0.86
  • Apart 0.74
  • What does this indicate?

Adoption studies

  • With adoption studies we tend to compare the adopted child with the biological mother and the adoptive mother to see which correlation coefficient is highest
  • Eg
  • Child and adoptive mother 0.42
  • Child and biological mother 0.72
  • Answer questions 4 and 5 on your handout
  • Mental Illness
  • Joseph (2004) the concordance rates for Schizophrenia is 40% for MZ twins and 7% for DZ twins.
  • However Tienari et al (1994) provide evidence of the diathesis stress model which encompasses both genes and environment.

Further Evaluation

  • Do twins, siblings and adopted and biological children always share the same environment?
  • What do you think ??

So how do we explain the fact that MZ twins reared together do not always show perfect concordance rates ?

The Human Genome Examples of the effects of genes on human behaviour

  • Intelligence
  • Chorney et al (1998) have identified individual genes associated with a high IQ through gene mapping.
  • However Turkheimer (2003) states socio-economic status is more important when accounting for variance in IQ scores.
  • Mate preference
  • Evolutionary studies like that of Buss (1989) suggests that adaptive behaviours are passed on in our genes e.g women preferring ambition and industriousness
  • However, Buss also found cultural variances and exceptions – 22% of women did not prefer ambition and industriousness.


  • Answer questions 6-8 on your handout.

Objectives Lesson 3

  • To be able to describe and evaluate 3 pieces research into environmental influences on behaviour
  • To understand the term ‘neural plasticity’
  • Aggression Social Learning Theory
  • Bandura’s classic bobo doll study illustrates the importance of vicarious reinforcement and the environment on our behaviour
  • However Coccaro et al (1997) suggest 50% of variance in aggressive tendencies is due to genes.
  • Neural plasticity
  • This is the ability of the brain (as in it’s physical structure) to change according to experiences and environmental factors
  • For example in Maguire et al 2000 the hippocampi of London Taxi drivers were found to be larger.
  • Evaluation ?

Research Study

  • Blakemore and Cooper (1970)
  • See page 70 of textbook
  • What is the key message of this study?
  • Evaluation ??
  • Answer question 9-12 on your handout.

Objectives Lesson 4

  • To understand how genes and the environment can interact with each other.
  • To prepare an essay plan for the question
  • Discuss the influence of genetic factors on human behaviour (22)

Nurture affects nature!

  • Look at pg 72 of your textbook
  • Look at the picture of identical twins separated at birth
  • Environmental factors such as stress or poor diet can switch on certain genes which are then passed on to the next generation. This is called epigenetics

Nature affects Nurture

  • Do parents treat all their young children exactly the same way? Why? Why not?
  • Reactive influence - Genetic factors like temperament can create a microenvironment.
  • e.g an aggressive child may be treated with more aggression.

Nature affects Nurture

  • Passive Influence - Genetically determined behaviour of parents might influence environment.
  • e.g mental disorder of parent may cause environment which triggers disorder in child.
  • Active influence Genes may influence actively selected parts of unshared environments in siblings – niche picking e.g Child with high IQ seeks challenging books, sporty child prefers outdoor activities – this has the effect of increasing the genetic characteristic.


  • Many examples demonstrate the interaction between genes and environment.
  • Another good example is Phenylketonuria- this prevents the amino acid phenylalanine being metabolised causing brain damage.
  • However if this is detected at birth it can be prevented through diet. So is it due to nature or nurture?


  • Complete the gap fill on your handout and then start work on your essay plan.

Key word check

  • Epigenetics
  • Reactive influence
  • Passive Influence
  • Active influence
  • Microenvironment
  • Niche-picking
  • Watch this
  • Bear in mind the debate!

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