Psychology of Crime
September 26 , 2012
Week 3, Wednesday
Role of genetics on crime:
• criminality was inherited
• resemble primate in appearance and behaviour
• Born criminal had physical defects
• as well as in the way the walk, looked and behaved.
Sloping and protruding foreheads, unusual ear size, lower jaw is protruding from the face, symmetry is
not present between left and right sides, longer arms. Lombroso was the first to say that criminality is a
Estimating Influence of Heritability
family studies, twin studies and adoption studies.
Juke family study:
By richard L dugdale:
An investigation of the hereditary line of a family in New York (709 family members)
60 habitual thieves, 7 murderers, 50 prostitutes.
Concluded genetics, shared environment played role.
Problem with the study: not all the 709 family members were related by blood. They were married in
Dizygotic Twins: fraternal- two different eggs, only case where you can have a girl and boy.
Genetically as different as non-twin siblings.
Monozygotic: Identical twins
Same egg- split it two. Share same genes, DNA.
Degree to which related pairs of subjects demonstrate a particular behaviour or condition.
• % rate
• What's the percent of twins that both engage in crime, or both do not engage in crime.
Monozygotic vs. Dizygotic:
If genes influence crime, identical twins should have a higer concordance rate for having a criminal
history that fraternal twins.
B/C MZ twins share more genetic make-up. Twin Studies:
Lange 1929 Twin Study:
Compared criminality of MZ and DZ twins.
MZ = 77% criminality (13 pairs)
DZ = 12% criminality (17 pairs)
MZ = 55% similarity (339 pairs)
DZ = 17% (426 pairs)
Twin studies: Effect of environment
• Prenatal, family, home.
• Affects twins in the same way, makes twins more similar.
• Influences often decrease as child grows.
Non shared environments:
• Interests, activities, friendships.
• Makes twins dissimilar
• Influences often increase with age.
Identical twins may be more similar in criminality because they shared the same environments
(growing up, prenatal, home etc)
Example: FASD, crime models
Was it the shared environment? Or was it the genes that makes the rate so high with identical twins?
Deals with shared environment confound.
Compare concordance rates of:
• Children and their biological parents vs.
• Children with their adoptive parents.
Higher concordance rates between biological parents, and their adopted-away children indicates a
genetic influence on the trait/behaviour. (biological parents have