1. Theories of Biology
Raine, Bruner, Daly and Wilson
2. The theory of biology
• The basic assumption here is that criminals are
biologically different to non-criminals. In
particular, some bio-psychologists argue that
special structures inside the brain control our
social behaviour. People without these
structures may become criminals.
• However, these theories are often reductionist
and deterministic and can only explain certain
types of crime.
• It has been shown that males often commit
crimes more than females.
• It has been suggested that this could be due to
an evolutionary trait.
• Males who were aggressive, could fight, run and
take risks, etc, would survive more in times
when such behaviours were necessary, those
who were not aggressive died and so the
necessary genes were passed on.
Brain abnormalities in murderers
indicated by PET
• Earlier work by Raine indicated a relationship
between low levels of activity in the prefrontal
cortex and violent behaviour.
• This is an area of the bran behind the forehead
and is often described as being the ‘emergency
break on behaviour’, as it prevents us from
acting on violent or aggressive impulses.
• To investigate patterns of brain activity in
murders compared to a matched sample of non-
murders using PET scanning.
• An experimental group of 41 participants charged with
murder or manslaughter who had pleaded not guilty for
reasons of insanity- NGRI- but had been convicted.
• Mean age of 34.3.
• 39 men and 2 women.
• 23 had a history of brain damage, 6 had schizophrenia, 3
substance abuse, 2 affective disorders, 2 epilepsy, 3
learning difficulties and 2 with paranoid personality
• A control group of 41 people matched on sex and age,
mean of 31.7 years, and were similar in other ways- 6
• Participants were screened and showed no
history of psychiatric illnesses.
• No participants were currently on medication.
• The IV was whether a participant was a
murderer or not, and the DV was the measures
of brain activity and brain structure found using
the PET scanner.
9. What is a PET scan?
• A brain Positron Emission Tomography can is an
imaging test that uses a radioactive substance to
look for disease or injury in the brain. A small
amount of this material is given through the vein
on the inside of the elbow. It travels through the
blood and collects in organs and tissues. It helps
the radiographer to see certain areas more
• The PET scanner detects signals from the tracer
and a computer changes this into a 3D image.
• There was no difference
in task performance, but
significant differences in
the brain metabolism of
glucose in a number of
areas between murderers
Area of the brain Findings
Prefrontal cortex Lower glucose
activity- in some
Limbic system Different levels of
activity in the
• The study shows that murderers pleading NGRI
have significant differences in glucose
metabolism in certain areas of the brain
compared to the non-murderers.
• Reduced brain activity in certain areas may be
one of the many predispositions towards
• The areas identified as having abnormal activity
are associated with; a lack of fear, lower self-
control, increased aggression, impulsiveness,
problems controlling and expressing emotions.
• Ecological validity
– Used real criminals as well as a control group
– Can only be generalised to violent criminals
– Can be applied to trials
– Can help with rehabilitation after brain injuries
• Free will vs Determinism
– Brain structure determines criminality
• Nature vs Nurture
– Biology changes in the structure of the brain lead to
A study of violence in a family of
• Genes are the building blocks of DNA and tell our bodies
how to grow and develop.
• Our genes do not know anything about the laws and
constructs of society so criminality is not directly affected
by our genes. However, genes can give people
predispositions- a natural, built-in tendency to behave
in a certain way- for example taking risks, being
aggressive or selfish.
• These predispositions may lead to a person behaving in
a way that leads to criminal behaviours.
• To study a family where males were affected by
a syndrome of borderline mental retardation and
abnormal violent behaviours.
• A case study of a family from the Netherlands.
• 5 affected males were studied who showed
behaviours such as impulsive aggression, arson,
attempted rape and exhibitionism.
• Data was collected from the analysis of urine
samples collected over a 24 hour period.
• The tests showed disturbed monoamine
metabolism associated with a deficit of the
enzyme monoamine oxidase A.
• A mutation was identified in the X chromosome
of the gene responsible for the production of
• MAOA is involved in serotonin metabolism.
• An impaired metabolism of serotonin is likely to
be responsible for mental retardation and could
be linked to the aggressive behaviour.
– Small sample- only 5 boys from 1 family
– Could this just be an ‘odd’ family?- not like the rest
• Quantitative data
– Urine samples were taken which increases the
• Reductionism vs Holism
– Puts behaviours down to genes and mutations within
• Psychology as science
– Objective measures
22. Daly and Wilson
Investigation of gender-related
• In all cultures, young males appear more often
in crime statistics than any other group.
• Daly and Wilson noticed that young male
offenders have a short term horizon where
they want instant gratification. They also have a
short lifespan expectation die to the risky
behaviour that they engage in.
• To find out if homicide rates would vary as a
function of local life expectancy in Chicago.
• A correlational study using survey data from
police records, school records and local
demographic records in Chicago.
26. Why Chicago?
• Chicago is an unusual American city because it is
divided into 77 distinct community areas or
• These areas have fairly clear cut boundaries and their
own social and economic characteristics.
• The researchers took their data from a recent population
census and compared it to police and school records on
crime, delinquency and truancy.
• They focussed on the communities that had a low
average life expectancy for males aged 54-77 years.
• The results showed that life expectancy was a good
predictor of neighbourhood homicide rates.
• There was a negative correlation; the lower the life
expectancy, the higher the homicide rate.
• The correlational coefficient was -0.88, which is very
• Daly and Wilson suggest that young men in these areas
have the ‘short term horizon’ described earlier. They
want instant gratification rather than delayed pleasure
and expect to live short lives and discount the future.
• Another finding was a negative correlation
between truancy from school and life
expectancy. This could be explained by a short
term horizon again.
– The boys see little point in working hard at school
because they do not imagine long futures for
themselves and their parents don’t force them to
attend because they also operate on a short term
– The payoff is then that young males who skip school
and break the rules will have more potential friends,
compensating for them dying younger.
• Young men from disadvantaged neighbourhood
expect to live shorter lives, therefore are more
likely to engage in risky behaviours.
• These findings can be explained by social
factors such as poverty and inequality.
• Correlational study
– Does not show cause and effect
– Data gathered from police and school records
– Only used people from Chicago
• Reductionism vs Holism
– Biological explanations
• Free will vs Determinism
– Biology determines behaviours