1. Psychology

2. Learning objective
New title: Biological explanations for criminal behaviour

3. Learning Outcomes Consider what we mean by ‘genes’
Find out some biological explanations for behaviour

4. Biological explanations for criminal behaviour
We all have genes. Let’s start at the beginning:
Genetic Similarity: We All Have the Same Genes
Each person has the same set of genes - about 20,000 in all.
The differences between people come from slight variations in these genes. For example, a person with red hair doesn't have the "red hair gene" while a person with brown hair has the "brown hair gene."
Instead, all people have genes for hair colour, and different versions of these genes dictate whether someone will be a redhead or a brunette.

5. Biological explanations for criminal behaviour
The Basics of DNA
Your body contains 50 trillion tiny cells, and almost every one of them contains the complete set of instructions for making you.
These instructions are encoded in your DNA. DNA is a long, ladder-shaped molecule. Each rung on the ladder is made up of a pair of interlocking units, called bases, that are designated by the four letters in the DNA alphabet - A, T, G and C. 'A' always pairs with 'T', and 'G' always pairs with 'C'.

6. Biological explanations for criminal behaviour
DNA is Organised Into Chromosomes
The long molecules of DNA in your cells are organised into pieces called chromosomes.
Humans have 23 pairs of chromosomes. Other organisms have different numbers of pairs - for example, chimpanzees have 24 pairs.
The number of chromosomes doesn't determine how complex an organism is - bananas have 11 pairs of chromosomes, while fruit flies have only 4

7. Biological explanations for criminal behaviour
Chromosomes: Boy or girl?
A newly fertilised egg usually has 46 chromosomes, arranged in 23 pairs. One pair of these chromosomes decides whether the embryo will grow into a boy or a girl: the sex chromosomes, X and Y – named after their shapes. A fertilised egg with two X- chromosomes will grow into a girl, and one with one X and one Y will grow into a boy.
The sperm cell has the deciding chromosome. It is from conception as to whether a person will become male XY or a female XX.

8. Biological explanations for criminal behaviour

9. Biological explanations for criminal behaviour
Chromosomes:
Sometimes, chromosomes are not so straight forward.
Some families carry genes which creates a difference in their off spring.
Haemophilia is one example of this:

10. Biological explanations for criminal behaviour
Chromosomes:
Adults and children with Downs syndrome are born with an additional chromosome on the 21st pair.

11. Biological explanations for criminal behaviour
Chromosomes:
Some people are born androgynous. This is when the genes have not dictated either a male gender or a female gender.
This is when the second X or the Y chromosome is missing.

12. Biological explanations for criminal behaviour
Chromosomes:
The XYY gene.
This has been linked to increased aggression and violence.
Why would a female not have the XYY chromosome?
We will look more in detail at this in a study by Theilgaard (1984)

13. Biological explanations for criminal behaviour
New title:
Methods to compare biological links to criminality.
Firstly, Summarised what we have covered about the chromosomes
hint:
Chromosomes are part of our DNA.
There are 23 pairs (46 single).
Differences occur: males vs females (explain)
Downs syndrome (explain)
Androgynous (explain)
XYY chromosomes (explain)

14. Biological explanations for criminal behaviour
Family studies
This is when psychologists compare the family trees of criminals and non-criminals.
What weakness’ are there with this? Consider SLT and what we learned about Bundy, Toores and Pittman.

15. Biological explanations for criminal behaviour
Adoption Studies
These are normally carried out through comparison case studies, such as adoption studies.
Mednick (1984) Examined 14,427 adopted children. He examined how many adopted children had criminal records, in comparison to their biological parents.
He found that adopted children with criminal records for property theft, also had biological fathers with criminal records, suggesting a possible genetic link.
Again, what are the weaknesses?

16. Biological explanations for criminal behaviour
Twin Studies
There are two types of twin – MZ (monozygotic / identical) and DZ (dizygotic / non-identical) who shared 100% and 50% of their genes respectively.
Christiansen (1977) examined 2586 pairs of twins in Denmark. He found a concordance rate of 52% for MZ and 22% for DZ. That is, if one MZ twin was a criminal, there was a 52% chance the other would be. This link was found for property crime not violent crimes.
What does the difference in % between MZ and DZ indicate?
What do twin studies suggestion about the role of nature vs. nurture for criminality?

17. Biological explanations for criminal behaviour
Type of research
Evidence for biological causes
Evidence against biological causes
Chromosome XYY
Family Studies
Adoption Studies
Twin Studies