1. Researchers study genetic factors related to aggressive behavior using twin and adoption studies to separate genetic and environmental influences. Twin studies compare rates of aggression in monozygotic (identical) twins who share all genes versus dizygotic (fraternal) twins who share about 50% of genes. 2. Meta-analyses of twin and adoption studies suggest genetics can account for around 50% of the variability in aggressive behavior, though the environment also plays a role. 3. While early research linked traits like the XYY genotype to increased aggression, later studies found no single genetic characteristic was associated with aggression, suggesting the initial genetic views of aggression were overemphasized.

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10 minutes

2. Genetic Factors in Aggressive
Behaviour

3. How do researchers study genetic
Draw on your factors?
research methods Twin Studies
knowledge - Monozygotic twins share all of
their genes where as dizygotic
Adoption Studies twins share only about 50%
- Researchers compare the
degree of similarity for
-Separate the effects of genes
aggression to look for a
from that of the environment
concordance rate.
-If there’s a +ve correlation in
- If the concordance rate is
aggressive behaviour in
higher in MZ twins it suggests
adopted children and their
the behaviour has a genetic
biological parents it suggests
component
the behaviour has a genetic
component

4. Genetics and Aggression
Studies often find that aggressive children have aggressive parents
Miles & Carey (1997)
Carried out meta-analysis of 24 twin and adoption studies
Results suggested a strong genetic influence that could account
for as much as 50% of the variance in aggression

5. Genetics and Aggression
Studies often find that aggressive children have aggressive parents
Other research focussed on the genes themselves and tried to
identify important characteristics of genes that might cause these
aggressive tendencies – much of this research has focused on
chromosomes
Sandberg (1961) first identified the 47 XYY karotype. Whilst
most normal individuals have 46 chromosomes (23 from each
parent), it’s possible for a male to have an extra Y sex
chromosome, making the XYY

6. Genetics and Aggression
Studies often find that aggressive children have aggressive parents
The research of Court-Brown (1965-1967) found that those
with XYY would be ‘best hospitalised due to an increased
likelihood of aggressive behaviour’
This was requested based upon common knowledge of traits
associated with each of the sexes.
Many textbooks and media depictions of the time adopted this
view contributing the widely held belief that XYY males are more
aggressive

7. Genetic theory Evaluation
Alternative Approach
Focussing so heavily on genetics ignores the
behavioural approach
Fails to account for the role of the environment
e.g. Bandura’s Bobo doll study demonstrated
that children were more likely to exhibit
aggressive behaviour when observed by a
rewarded adult role model
This suggests that environment and SLT may at
least play a part in aggression.

8. Genetic theory Evaluation
In addition to this:
A replication of Bandura’s
research using twins found
no difference in correlations
between MZ and DZ twins
- Suggesting that aggression
may be more a product of
the environment

9. Genetic theory Evaluation
Alternative Approach
Nature Vs. Nurture
Aronson (1999) reported on non-violent the
Focussing so heavily on genetics ignores
behavioural approach
societies
This suggests thatfor the role of the environment
Fails to account learning is more important that
e.g. Bandura’s Bobo doll study demonstrated
biology when explaining aggression
This is critical as were if therelikelybiological
that children even more are to exhibit
influences Aronson’s researchobserved by a
aggressive behaviour when shows that the
environment can role model
rewarded adult override them
If aggression is that environment and SLT may at
This suggests biological then it would not be
least playspecific in implying aggression is learned
culturally a part – aggression.

10. Genetic theory Evaluation
Nature Vs. Nurture
McGue et al (1992) correlation of MZ and
DZ twins
+0.43 for MZ, +0.30 for DZ
Suggesting that genes play some part in
aggressive tendencies as MZ twins share more
DNA than DZ twins – suggesting genes play a
part

11. Genetic theory Evaluation
A03
In addition to this:
The reason MZ Bandura’s
A replication of twins are
more similar that DZfound
research using twins might
be due to environmental
no difference in correlations
factors – MZ twins are
between MZ and DZ twins
-more likely thatbe treated
Suggesting to aggression
may be more a product of
the same
the environment
They share nature and
nurture

12. Genetic theory Evaluation
Theilgaard (1984) researched Lagerspetz (1979) bred 25
the traits of XYY men compared generations of mice – in each
to XY men (including comparing generation the more aggressive
aggression levels). mice were made to breed,
It was found that no single similarly with the least aggressive
characteristic (except height) was mice.
associated with the XYY condition This resulted in 2 very different
Suggests that the initial view strains of mice
of XYY genotypes influencing
aggression may have been One group were super-aggressive
overemphasised and the other more docile