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Class notes Unit 2 2.1 Biological theories Criminology
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Biological theories UNIT 2 2.1Genetic theory-
If a crime is inborn, like Lombroso states, this would mean that it is presumably passed down
from parent to child
The Cambridge Study in delinquent development
This is a prospective longitudinal survey of crime and delinquency in 411 males mostly born in
1953. The study starts when the males are between the ages of 6-10 on why they might be a
criminal later in life. The factors include:
• Antisocial behaviour (playing up in school)
• ADHD and other hyperactive disorders
• Low intelligence
• Family criminality
• Family poverty
• Bad parenting
Twin studies
Genetic theories have used studies of identical (monozygotic [MZ] ) twins as a way to test their
theory of criminality. MZ twins share the same genes as they came from the same egg.
Christiansen study-
This study was of 3586 twin pairs in Denmark. There was a 52% concordance rate between MZ
twins (when one twin has a conviction there’s a 52% chance the other twin also has a conviction)
whereas non identical twins (DZ) has a concordance rate of only 22%.
Johannes Lange-
They studied 30 pairs of twins who were the same sex. 17 of these pairs were DZ twins and 13
were MZ twins. They found that at least one of a pair was known to have committed a crime. They
also found that 10/13 of the pairs of MZ twins were both criminals whereas only 2/17 of the pairs
of the DZ twins were both criminals.
Strengths of Twin Studies Weaknesses of Twin Studies
• Because MZ twins are genetically identical it • If genes were the only cause of criminality,
is logical to examine whether their identical twins which are
offending behaviour is also identical 100% concordance but studies only show
• Twin studies that have been done, do give around half or less.
some support to genetic explanations. • Higher concordance rates between identical
twins may be due to sharing the same
homeschool et cetera. The shared
environment, school etc. are also share
similarities in their criminal behaviour, not
just identical genes.
• Parents often treat identical twins more alike
than they do not identical twins. Also,
identical twins may feel closer than non-
identical twins do so wondering may be
influenced by the others
criminality. Environmental factors may also
produce similarities in behaviour.
• It is impossible to isolate and measure the
effect of genes separately from
environmental effects
, Biological theories UNIT 2 2.1
Adoption Studies-
Researchers have also used adoption studies to test for a genetic cause of crime. These studies
compare adopted children both to their biological birth parents and to their adopted parents. The
thinking behind adoption studies is that an adopted child (especially if adopted soon after
birth) shares the same environment as their adoptive parents, but the same genes as their
biological parents. If we find that the adoptees behaviour in regard to criminality is more similar
to their birth parents’ behaviour, this would support a genetic explanation.
Evidence
Mednick et al examined data on over 14,000 adopted sons in Denmark from 1924 to 1947. They
found that sons were more likely to have a criminal record if a birth parent also had a record (a
concordance rate of 20%). This supports a genetic explanation. By contrast, they found that a
smaller proportion (14.7%) had a criminal record if their adoptive parent had one.
Hutching and Mendick compared adoptees with and without criminal records. They found that
adoptees with criminal records were more likely to have biological parents with criminal records
than adoptees whose birth parents did not have criminal records.
Strengths of Adoption Studies Weaknesses of Adoption Studies
• Adoption studies overcome the problem • Gottfredson & Hirschi argue the adoption
faced by twin studies, where biologically studies show genes have little effect on
identical twins are brought up in the same criminality
household, which makes it impossible to • Adopted children are often placed an
separate out the influence of genes from environment similar to those of their birth
environment. family, with families of the same class and
• The research design is logical, in theory it ethnicity, in the same locality etc. Similar
allows us to see the relative importance of environments may produce similar behaviour.
nature versus nurture. • Many children are not adopted immediately
• Findings of adoption studies do give some after birth but remain with their biological
support to genetic explanations. They show family for some time. The early environment
adoptees are more likely to have criminal may be the true cause of their criminality.
records if the biological parents had criminal
records too.
Jacobs XXY Study
Abnormality of the sex chromosomes is another possible genetic cause of
criminality. Chromosomes are made of DNA and protein, and they are found in the nucleus of our
cells. Each chromosome contains many genes. Chromosomes carry all the genetic information
that we inherit from our parents.
Normally, we have 46 chromosomes, arranged in 23 pairs (half from each parent). One
pair consists of our sex chromosomes and determines whether we are male or female.
Our mother’s two female chromosomes are known as XX and our father’s two male chromosomes
are XY.
Because we inherit one chromosome from each parents, we will have either:
• Two Xs: one from each parent. If we have XX we will be female.
• Or an X from our mother and a Y from our father. If we have XY we will be male. It is the Y that
makes it male
However, sometimes there are abnormalities. One is an extra Y (male) chromosome. The is known
as XYY syndrome and has been labelled the ‘super male syndrome’. Men with XYY tend to be very
tall and well build and of a lower intelligence. Jacob et al claim that men with XYY syndrome are
more aggressive and potentially more violent.
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