Adoption Studies Flashcards
What do twin studies compare the likelihood of?
Criminality between monozygotic (identical) and dizygotic (non-identical twins)
How many genes do monozygotic twins share?
100%
How many genes do dizygotic twins share?
50%
How many twins did Christiansen study?
3,586 twin pairs
Where did Christiansen study the twins?
Denmark
What was the concordance rate between monozygotic twins?
52%
What was the concordance rate between dizygotic twins?
22%
What does it prove if an adopted child portrays similar behaviour to biological parents?
That behaviour is genetic, and criminality is inherited.
Nature not nurture.
What does it prove if the adopted child portrays similar behaviour to adoptive parents?
That behaviour is learnt, and criminality is a result of upbringing.
Nurture not nature.
When was the Mednick study?
1967
How many criminal records did Mednick study?
Over 14,000 adopted sons records
What did he do with the records?
Compared them with the sons biological parents.
What did it mean for the son if his parent(s) had been convicted of a crime?
The son was more than twice as likely to be convicted of a crime themselves.
What did it mean for the son if his adoptive parent(s) were convicted of a crime?
It had far less an affect on the sons behaviour.
What chance did biological siblings have of both commuting a crime if they were both raised in the same environment?
30% chance.
What chance did adoptive siblings have of commuting a crime if they were raised in the same environment?
8% chance.
Who was Jefferey Landrigan?
A man who was abandoned at a daycare, adopted, and became a criminal.
What kind of environment was Landrigan adopted into?
A rich family, who gave him a good start in life.
What crimes did he commit?
Arrested for burglary at age 10
Murder at 20
What was discover about his family?
His father was a murderer and his grandfather was a their.
What does this prove?
That behaviour/criminality is inherited
Landrigan had a genetic predisposition to murder.
Three strengths of adoption studies
Only study to find a direct comparison between nature and nurture, they isolate the influence of the environment from those of genetics, and they are longitudinal studies - meaning the same child/children can be studied throughout their life.
Three weaknesses of adoption studies
Adoption process isn’t always random and children are often placed with parents like their families, adoption is a rare process so it’s a small sample to study (not representative), and it’s difficult to separate genetics from environment.