NATURE NURTURE DEBATE

1
NATURE NURTURE DEBATE

• Nature behaviour determined by inherited
  factors
  
• Nurture influence of environmental
  factors
  
• Or
• HEREDITY vs ENVIRONMENT

2
HISTORY OF DEBATE

• Philosophers - Plato inborn/native to an
  individual referred to naturism
  
• - Locke opposing view empiricism. Mind
  is tabula rasa
  
• Empirical means discovering through our senses.
• Implication of debate if learned, we can do
  something about it. Dont
  
• have to adopt either end of debate. Clear that
  it is an interaction between
  
• the two.

3

• Phenylketonuria
• An example which demonstrates interaction.
• A condition in which proteins are not processed
  properly. Leaves poisons in
  
• the blood that causes brain damage.
• Diathesis stress model
• Anorexia MZ twins not 100 concordance
  therefore interaction
  
• Heritability
• A measure of the relationship between
• a) variance of a trait in whole population
• b) extent to which variance is due to genetic
  factors
  
• Expressed as a ratio
• H. Ratio Genetic variance
• Total variance

4

• Genotype Phenotype
• Genotype - genetic constitution
• (genetic potential for who you might
  become).
  
• Phenotype - observable characteristics, eg.
  hair is brown (genotype) but
  
  
• bleached by sun.
• Phenotype is blonde.
• IQ we cannot access genotype. Even at birth,
  we cannot access pure
  
• genotype, all wombs vary.
• Transgenerational effect poor diet in pregnancy
  foetus suffers.
  
• If the foetus is female, her eggs will be
  affected. May appear to be inherited
  
• but it is in fact environmental (e.g. famine two
  generations ago increased the
  
• incidence of diabetes now).

5

• Form of interaction
• Plomin identified three ways nature and nurture
  interact.
  
• Passive heredity environment
• Intelligent parents educate their kids and make
  their environment educational. Parents have
  intelligent genes. Parents genes are
  transmitted passively.
• Reactive heredity environment interaction
• Research shows that parents react differently to
  a beautiful/plain child. They find it easier to
  relate to a child with easy rather than difficult
  temperament. So childs inherited
  characteristics create a reaction in others which
  changes childs environment.
• Active heredity-environment interaction
• As a child interacts with their environment it
  is altered and this in turn affects behaviour of
  the child. This is reciprocal determinism.

6
RESEARCHING NATURE AND NURTURE

• Twin studies are not strictly experiments. They
  simply compare individuals with
  
• the same or difference genetic make-up.
• IDENTICAL MONOZYGOTIC (single egg)
• NON IDENTICAL DIZYGOTIC (two eggs)
• DZ twins are the same as siblings except that
  they share a more similar
  
• environment.
• Twin studies are NATURAL EXPERIMENTS because
• IV (genetic relatedness) is not directly
  controlled by E.
  
• Ps are not randomly allocated to conditions.
• However, MZ twins are different in small ways
  right from conception. So the
  
• Nature-Nurture debate can never by truly
  investigated.
  
• MZ twins are not identical because
• Cells mutate and many mutate differently in each
  zygote.
  
• Each twin sets up its own micro-environment.
  Reciprocal determinism states that we each have a
  part in creating our own environment and MZ twins
  will always react slightly differently.

7

• Twins reared apart
• Shields classic study 1962 on IQ.
• Twins reared together Twins reared apart
• Concordance 0.76 Concordance 0.77
• Suggests very little environmental influence.
• but
• Kamin noted that twins had spent time together,
  or were raised by relatives and
  
• went to same school.
• Adoption poses a similar problem. Adoption
  agencies try to find an adoptive
  
• home which is similar to natural home.
• Shared and Non-shared environments
• Harris proposed that shared environments are in
  fact very different. This
  
• accounts for big personality differences between
  siblings.
  
• 50 of adult characteristics are thought to be
  genetic
  
• so
• 50 is environmental. This must include peer
  influences and therefore not
  
• shared.

8
Resolving the controversy

• Gottesman Reaction range
• genotype
• Genetic make-up - limits potential
• Environmental opportunities - actual
  development
  
• phenotype
• Look at blue box p356 (green)
• Racial Differences
• Jensen 69 produced evidence to show that black
  Americans were 15 IQ points
  
• below white Americans. (But 20 of blacks have a
  higher IQ than the average
  
• American).
• but
• between group differences are environmental. We
  cannot be certain that the
  
• difference is genetic unless they share identical
  environments.

9

• Practical and Political Consequences
• The interactionist position
• If high IQ can be enhanced, then Operation
  Headstart programmes should be
  
• encouraged.
• UK Burts IQ studies stated that IQ was largely
  inherited. It was on his
  
• research that the 11 was established, so that
  high IQ children were taught
  
• apart from low IQ ones.
• but
• Self-fulfilling prophecy operates.