Twin Studies

Question 1

What are twin studies?

Answer 1

• support the idea that heritable traits may increase the risk of criminal behaviour

Question 2

What is it called when twins share a characteristic?

Answer 2

• concordance rate

Question 3

What are monozygotic twins?

Answer 3

• identical twins
• come from same fertilised egg
• share 100% DNA

Question 4

What are dizygotic twins?

Answer 4

• non-identical twins
• come from two separate eggs
  share 50% DNA

Question 5

Which twins show a higher concordance rate?

Answer 5

• monozygotic twins

Question 6

What does it mean if criminality is genetic for twins?

Answer 6

• if one MZ twin is a criminal, so should the other one

Question 7

What did Johannes Lange find out about twins?

Answer 7

• found that MZ twins showed much higher degree of concordance than DZ twins for criminal behaviour
• 10 of the 13 MZ twins had both served time in prison
• only 2 of the 17 DZ twins had such concordance

Question 8

What did Christiansen find out about twins?

Answer 8

• studied 3,586 twin pairs in Denmark
• 52% concordance rate between MZ twins
• there was a 22% concordance rate in DZ twins

Question 9

Strengths of twin studies

Answer 9

• supporting evidence for inheritance - Lange (1929) found that MZ twins showed a much higher degree of concordance than DZ twins for criminal behaviour
• supporting evidence from Christiansen (1977) found that MZ twins show a 52% concordance rate, whereas DZ twins only share 22%
• it is logical to study MZ twins + their genes are identical - so it makes sense to examine whether their offending is also identical

Question 10

Weaknesses of twin studies

Answer 10

• early research has been criticised for lack of control - there was no DNA test to check if the twins were actually MZ or DZ - so this was done purely based on appearance which is not very valid
• concordance rates are never 100% - which means that genetics can not be the only cause of criminal behaviour - studies show that concordance rates of 50% or less meaning that other factors must play a role
• it is impossible to isolate + measure the effects of genes separately from the effects of the environment as the environment can affect behaviour from the moment you are born + even before then