What is Crime? What makes people commit crimes? Are there different causes for different crimes?

Why?

Biological explanations for criminality The first thing to ask yourself is: – How can I measure the biological influences associated with criminality?

Concordance rates What is a concordance rate? When we want to see if two variables are related, we conduct a correlation study. The statistical test for a correlation gives us a correlation coefficient, which tell us the likelihood of both variables happening together (i.e. how related they are). If we convert our correlation coefficient into a percentage (multiply by 100), this is our concordance rate. The higher the concordance rate is, the more chance that both variables will occur together. Example: if we do a test to see how often a child becomes a criminal if their mother is also a criminal and we get a concordance rate of 80%, it means that there is an 80% chance that a child with a criminal mother will also be a criminal. Measuring the biological link

How can we test if genes play a part in criminal behaviour? Who can we study? – Twin studies: monozygotic twins dizygotic twins – Adoption studies: – Family studies: looks at family trees  All 3 of these research techniques can give us an idea of whether it is our genes or our environment which is influencing criminality.  All 3 of them use concordance rates.

Twin Studies Monozygotic twins - Identical Share 100% of their genes The only thing that could be different between them is their environment e.g. they might become friends with different people at school etc. If it’s true that our genes are the only cause of criminality, then if one twin is a criminal then the other definitely will be. If only one twin is a criminal, then this would suggest that it isn’t just our genetics at work, maybe the environment has an influence too.

Twin Studies Dizygotic twins – Non-identical Share 50% of their genes – they share just as much of their genes than they do with a sibling not born on the same day If both twins are criminals, this would support the idea that criminality is caused by the environment

Twin Studies – an example Christiansen (1977) Found a 52% concordance rate in monozygotic twins 22% concordance rate in dizygotic twins This link was only found for property crime (e.g. theft), not violent crime What do these findings tell us?

Adoption Studies Share genes, but not environment Compare concordance rates between children and their biological parents with concordance rates between children and their adoptive parents If concordance rates are higher for the biological parents than adoptive ones, this would suggest a biological cause (the child is more like them even though he/she wasn’t raised by them) & vice versa Twin Studies Share genes and environment Compare concordance rates between one twin and another If concordance rates are higher for MZ than DZ twins, this would suggest a biological cause (the only difference between MZ & DZ is genes) & vice versa

Adoption Studies – an example Mednick (1984) Adopted children that had criminal records were more likely to have biological fathers that were also criminals, even though these fathers didn’t bring them up This was true even if 2 siblings were adopted to different families What do these findings tell us?

Evidence from both twin, adoption, and family studies show that people are more likely to turn to crime if they have family members who were also convicted of crime. This could therefore support the idea that there is a genetic basis for criminality. Could we explain this conclusion in any other way? (not using a bio explanation)

Biological explanations for criminality – How could our genes affect our likelihood to turn to crime?

Chromosomal abnormalities The sex chromosome pair determines whether you will become male or female – XX = female – XY = male This is because the Y chromosome carries information which tells the body to produce male sex hormones, like testosterone What do we already know about testosterone? Could we link this to criminality? How our genes affect criminality

Chromosomal abnormalities Sometimes, things can go wrong during pregnancy which can affect the genetic make-up of a baby, meaning it’s not inherited so doesn’t run in the family Some male babies can be born with an extra Y chromosome (XYY) This can affect the boy’s behaviour later in life in many ways. Researchers have found that XYY males are more likely to be violent and criminal You can see if someone has this abnormality by taking a blood sample For example, blood samples of some murderers have revealed them to have XYY – Richard Speck (murdered 8 student nurses) – Arthur Shawcross (murdered 11 women) How our genes affect criminality