The nature-nurture debate

• What is the nature-nurture debate?

  The relative importance of heredity and environment in determining behaviour; the interactionist approach. 
• Heritability

  The heritability coefficient is a number from 0-1 which indicates the extent to which a characteristic has a genetic basis (a value of 1 means it is entirely genetically determined).
• Nature: innate and genetic influences, usually 0.5 heritability. 


  Early nativists argued that human characteristics are innate - the result of heredity. 

  The general figure for heritability of IQ is around 0.5 (Plomin). The fact this is not 1.0 suggests that genetics and environments are both important factors in IQ.
• Nurture: environmental influences (e.g. learning and experience pre- and postnatal).


  Empiricists (e.g. Locke) argued the mind is a blank slate at birth upon which experience writes - the behaviourist approach. 
• Nature-nurture debate - environmental influences


  Lerner has identified different levels of the environment:

  • Defined in narrow prenatal terms (e.g. the mother’s physical and psychological state during pregnancy).
  • Defined more generally through postnatal experiences (e.g. the social conditions the child grows up in).
• The relative importance of nature and nurture. 


  The nature-nurture debate is impossible to answer because environmental influences in a child’s life begin as soon as it is conceived (perhaps even earlier.)

  Practically and theoretically it makes little sense to try to separate nature and nurture (e.g. in twin studies it is harder to tell whether high concordance rates are the result of shared genetics or shared upbringing).
• Interactionism (e.g. attachment)


  The focus of the debate is no on the relative contribution of each influence.

  For example, the interactional approach to attachment sees the bond between infant and parent as a ‘two-way street’.

  • The child’s innate temperament influences how the parents behave towards them. 
  • The parents’ responses in turn affects the child's behaviour (Belsky and Bovine). 
• Interactionism in mental illness: the diathesis-stress model


  The diathesis-stress model suggests mental disorder is caused by a biological vulnerability (diathesis) which is only expressed when coupled with an environmental trigger (stressor). 

  For example, Tienari studied a group of Finnish adoptees and found that those most likely to develop schizophrenia had biological relatives with a history of the disorder (the vulnerability) and had relationships with their adoptive families described as ‘dysfunctional’ (the trigger). 
• What is epigenetics?


  Epigenetics is a change in genetic activity without changing the genetic code.
• Epigenetics is a change in genetic activity without changing the genetic code.


  Lifestyle and events we encounter (e.g. smoking, diet, pollution, poverty) leave epigenetic ‘marks’ on our DNA - these marks tell our bodies which genes to ignore and which to use, and may influence the genetic code of our children. 

  So, epigenetics introduces a third element into the nature-nurture debate - the experience of previous generations. 
• Nature-nurture debate - strength

  One strength is understanding the interaction may have real-world implications.

  Extreme beliefs in the influence of nature or nurture may have negative implications for how we view human behaviour. Nativists suggest genes determine behaviour and characteristics (‘anatomy is destiny’). This has led to controversy (e.g. linking race to eugenics policies, and advocating a model of society that manipulates its citizens). Recognising that human behaviour is both nature and nurture is a more reasonable way to approach the study and ‘management’ of human behaviour. 
• Nature-nurture debate - strength


  A further strength is evidence of the gene-environment interaction. Scarr and McCartney outlined three types of gene-environment interaction: passive, evocative, and active. The interaction is different for each type, e.g. in passive interaction parent’s genes influence how they treat their children (musically-gifted parents play to their children and encourage a love of music). Again, this points to a complex and multi-layered relationship between nature and nurture. 
• Nature-nurture debate - strength

  Another strength is understanding nature-nurture relates to other debates. A strong commitment to either a nature or nurture position corresponds to a belief in hard determinism. The nativist perspective suggests ‘anatomy is destiny’ while empiricists argue that interaction with the environment is all.  These equate to biological determinism and environmental determinism, showing how nature-nurture links to other debates. 
• Nature-nurture debate - limitation

  One limitation is the confounding factor of unshared environments. Research that tries to ‘tease out’ environmental influences is complicated by the facts that even siblings raised within the same family will not have identical upbringings. Dunn and Plomin suggest individual differences mean siblings may experience life events differently, as in age or temperament leads to a life event such as parental divorce having a different meaning to each sibling. This would explain the finding that even MZ twins reared together don't show perfect concordance rates.