2.2 Biological level of analysis
Genetics and behaviour
Learning Outcomes
• First four are the same as in 2.1
• New are:
• Discuss the extent to which genetics influence
behaviour
• Examine one evolutionary explanation of
behaviour
• Discuss ethical considerations in research into
genetic influences on behaviour
The developing child
http://www.learner.org/vod/vod_window.html?
pid=1502
This program traces the nature vs. nurture
debate, revealing how developmental
psychologists study the contributions of both
heredity and environment to child
development. With Dr. Renee Baillargeon of
the University of Illinois and Dr. Judy De
Loache of the University of Illinois
Is biology destiny?
Case Study
1. “A boy without a penis” handout
2. Money study on p. 37 same study
• Read and comment
• What is your response?
Behavioural genetics
• Deals with understanding how both genetics
and the environment contribute to individual
variations in human behaviour
• What is inherited may be one of the building
blocks for such complex behaviours
Behavioural genetics
• Psychologists argue that an individual may
have a genetic predisposition towards a
certain behaviour; however, without the
appropriate environmental stimuli, this
behaviour will not be manifested
• An example of this is: the origin of depression
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
Genes
• Humans have 24 distinct chromosomes, with
app.. 20 000- 25 000 genes
• Human genome project: mapping the genetic
make-up of the human species by identifying
those genes
• http://www.ornl.gov/sci/techresources/Huma
n_Genome/home.shtml
Genetic research
• Is to a large extent based on correlational
studies
What is that?
Twin studies, family studies and
adoption studies
• To study the possible correlation of genetic
heritance and behaviour
• But why?
Twin studies
• There are two types of twins: monozygotic
(MZ) and dizygotic (DZ)
• Monozygotic twins: are genetically identical
due to one fertilized egg that splits into two.
These twins are of
the same sex,
and look very much alike
Twin studies
Dizygotic twins are from two eggs.
• DZ twins are not any closer genetically than
brothers and sisters, that is, they will have
50% of their genes in common.
• They don’t have to be
of the same sex.
Twin studies
• The hypothesis is that the higher the genetic
relationship, the more similar the individuals
should be if the particular behavior being
studied is inherited.
• The correlation found is called the
concordance rate
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
Adoption studies
• Adopted or foster children generally share
none of their genes with their adoptive
parents, but 50% with their biological mother
and father.
Adoption studies
• Therefore, if the heritability of a behaviour is
high, the environment should have little part
to play
• And the adopted children should correlate
more strongly with the behaviour (e.g. IQ) of
their biological mother and father than their
adoptive parent.
Adoption studies
• Critique against using this method:
• Not representative of the general population
• Adoption agencies tend to use
selective placement when
finding homes
(as similar as possible)
Is Madonna a similar family?
To sum up
• These methods help the researchers to
determine the extent of genetic influence
• There is a clear correlation between several
behaviours and genetic heritance
• We are going to examine Intelligence