8.3.1 The Relative Importance of Heredity and Environment

What is the essence of this debate?

• This is probably the oldest debate in psychology and is based on the argument that it is either genes or environment that determine behaviour
• The nature side of the debate is based on the idea that heredity is key to human behaviour
• The nurture side of the debate is based on the idea that environmental influences such as family life, peers, education, culture are key to human behaviour
  
  

Can there only be one explanation for human behaviour? Which side do you favour?

• Behaviour is innate, a product of  genetic inheritance
• Behaviour can be understood by studying biological processes and structures such as hormones, neurotransmitters, regions of the brain
• Methodologies involved include brain scanning e.g. PET, MRI; concordance rates in twin studies; DNA analysis via urine or saliva samples 
• The extreme nature argument suggests that some behaviours are entirely biologically-based e.g. women are born to be carers whereas men are born to be providers
• Bowlby’s theory of attachment is an example of a pro-nature argument as he based his ideas on the work of ethologists such as Lorenz, concluding that attachment is an essential evolutionary mechanism needed for the survival of the species
  
  

The early work of ethologists supports the nature side of this debate but to what extent can we generalise from animal studies?

Arguments for nature

• Understanding genetic inheritance has helped to identify atypical chromosome patterns as seen in a condition such as Klinefelter’s syndrome, which is clear indication of a biological basis to behaviour
• The discovery of the nAChR nicotinic receptor in the brain is compelling evidence for a pro-nature explanation of nicotine addiction

Arguments against nature

• Using a purely nature-based approach can result in prejudiced, overly deterministic, possibly dangerous assumptions being made about people based on their gender, ethnicity, sexuality etc.
• Twin studies have failed to show 100% concordance between monozygotic (identical) twins which demonstrates that the environment also plays a role in behaviour, even for people who share exactly the same DNA
  
  

Identical (MZ) twins: an argument for or against the nature side of the debate?

• Behaviour is learned, a product of  environmental factors
• Behaviour can be understood by studying environmental influences such as upbringing, relationships, schooling etc.
• Methodologies involved include classical and operant conditioning; experiments on social roles such as the Stanford Prison experiment; field studies such as Schaffer and Emmerson (1964) 
• The extreme nurture view suggests that human beings are born as a ‘blank slate’ (the basis of hard determinism) which is ready to be ‘written on’ by life experiences
• The learning theory of gambling addiction is an example of a pro-nurture argument as it is based on the idea that the gambler is positively reinforced in their gambling behaviour and that this is strengthened every time they gamble, even if they lose money
  
  

Gambling may be a learned behaviour, strengthened by schedules of reinforcement

Arguments for nurture

• Behaviour can be shaped and changed by the environment as evidenced by the two-process model which states that phobias are learned via classical conditioning and reinforced via operant conditioning
• Theories such as the deprivation model of aggression demonstrate that the situation may prevail over individual personality traits thus it is the environment that produces aggression, not the person

Arguments against nurture

• Although twin studies do not show a 100% concordance rate they are still strong indicators that some behaviours may have a genetic basis e.g. Nan et al.’s (2012) found a 61%-80% concordance rate for obesity in a sample of 8000 MZ twins
• The nurture side of the debate cannot account for individual differences within children raised in the same family environment i.e. one child may become criminal while the other child does not; one child may develop a drug addiction while the other child does not
  
  

The prison environment may lead to aggression which would otherwise not have been seen from some individuals