Nature refers to inherited characteristics and nurture is the product of experience (environmental influences and learning). The philosopher John Locke claimed that at birth we are like a blank slate. We inherit nothing and all behaviour is acquired as a consequence of experience.
Nature and nurture interact rather than one or the other determining behaviour. The distinction made between genotype (inherited potential behaviour) and phenotype (observable behaviour) shows us that we can never actually access the genotype and therefore are always assessing nature and nurture jointly. For example, Nature—nurture influences are often researched using twin studies, and comparing monozygotic (identical) and dizygotic (non-identical) twins. However, we now realise that monozygotic twins are not exactly identical, partly because of small genetic differences and also because they create their own micro-environments (each child reacts to others in different ways; what they attend to and who they choose to interact with). The fact that twins who are reared apart often have similar environments further confounds the data.
Examples of the nature—nurture debate in psychology
Perception. To what extent is what we see—for example the perception of depth or visual illusions—an innate aspect of the physical visual system? Or are some aspects of perception learned and therefore different in different cultures? (see Deregowski)
Language. To what extent are humans “hardwired” to acquire language, or is their ability to use language based on exposure and imitation? If the latter is true, then it should be possible to train nonhuman animals, which don’t have the innate brain mechanisms, to use language. (see Gardner and Gardner)
Aggression. To what extent is violent behaviour an aspect of a person’s nature, or is it learned? For example we might propose that men are more aggressive than women because they are innately more aggressive or it may be that, in our society, men are taught to respond more aggressively than women (nurture). The question has important practical applications in the reduction of aggression. If it is down to nature, then drug therapies may offer the best means of prevention.
Gender development. Each individual’s chromosomes determine sex; gender identity and gender role behaviour are largely moulded by society though there is evidence that biology may play an important role.
Causes of mental illness. Recent research has found evidence of a genetic basis for many atypical disorders, however the diathesis-stress model suggests that a person’s genetic make-up will predispose them to certain disorders but environmental factors (stresses) actually trigger the expression of the disorder. The more susceptible an individual is, the fewer stresses are necessary. This means that neither nature nor nurture individually causes dysfunction. The disorder comes about as a result of the interaction of nature with nurture. (See Thigpen and Cleckley)
When psychologists explore the extent to which a characteristic is inherited they use a variety of measures.
The concordance rate expresses the extent to which two measures are in agreement. For example, if 20 twin pairs are studied and in 18 of them both had developed schizophrenia, this would produce a concordance rate of 18/20 or 90%, which is very high concordance. Alternatively one can correlate the IQ scores of two individuals, and the degree of correlation shows us how concordant they are.
Monozygotic (identical twins) have the same genes (100% concordance) whereas dizygotic (non-identical) twins and siblings are genetically 50% similar.
Where do the main approaches in psychology stand on nature—nurture?
The biological approach by definition takes a nature position.
The behaviourist approach is entirely on the side of nurture, though the potential for learning is innate.
The cognitive approach similarly makes no special claims for nature except in so far as the structure of the mental system is innate. Its development, however, is a response to experience.
The psychoanalytic approach combines both nature and nurture in the view that innate, sexual forces are modified by experience to produce adult personality.
The evolutionary approach is clearly nativist (nature).
The humanistic approach emphasises nurture but holds certain views about the nature of humankind—that it is positive, inclined towards psychological good health, and has the potential for self-actualisation.
The social constructionist approach is an example of the nurture approach. Social forces shape us.
Michael W.Eysenck & Cara Flanagan, 2001, Psychology for A2 level, Psychology Press, ISBN 1-84169-251-4 (Highly recommended text for broad overview of psychology, written in an easy to understand style)