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In what ways do nature – nurture interact?

The most common way to understanding the contribution of nature and nurture is by looking at twin studies. Monozygotic (identical) twins share exactly the same genetic makeup. Dizygotic (fraternal or non-identical) twins share 50% of the genes, just like ordinary brothers and sisters. The degree of similarity between monozygotic twins than dizygotic twins is often taken as an indication of genetic influence.

Twin studies have been conducted looking at intelligence, temperament and mental illnesses such as schizophrenia and have demonstrated a clear genetic influence in each case (Gottesman, 1991).

However, can you think what else should be considered when rating, i.e. the intelligence of monozygotic twins?

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Also think about how height is genetic, but what about the fact that Americans and Europeans have increased in height by over 5cm’s between 1920 – 1970. How could you explain this?

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Problems with measuring intelligence using IQ tests may be inaccurate. For example, they only measure certain aspects of intelligence, and practice at them will improve performance which could indicate a higher level of intelligence than someone who had never completed an IQ test before. Therefore these IQ tests lack reliability and sometimes validity too. Individuals will not get the same results each time – they will get better thus unreliable. The IQ test lacks validity as someone may not be good at maths but may excel artistically – does this mean they have a low IQ?

The use of twin studies, particularly monozygotic twins is also useful when understanding how much behaviour is due to the environment. Identical twins reared together are assumed to have the same upbringing, or do they?

1. Reactive ‘gene – environment’ correlations (or how people affect their environment)

Aggressive children tend to evoke aggressive responses and therefore experience aggressive environments. The same goes for children with a sunny disposition. So the genetic influences that produce aggression in a child therefore interacts with their environment to affect it, hence the use of the term ‘reactive’.

An example of a static ‘gene-environment’ correlation could be how an individuals biological make-up e.g. gender, affects how people respond to them. This is a fixed characteristic hence the term static (Rutter and Rutter 1992).

2. Shared and non-shared environments

Often the environment people live in is correlated to a personal characteristic, e.g. how low socio-economic class is associated with a higher incidence of schizophrenia. Within a family, siblings have a shared environment, yet they are rarely very similar in psychological characteristics. This may suggest that non-shared environments or experiences are most important in the development of psychological characteristics.

Even within the same family children have non-shared experiences, e.g. maybe one is treated more strictly that the others, the youngest could always be viewed as being spoiled or the middle could always feel like they are left out. Dunn and Plomin (1990) argue that the only way family influences could affect behaviour is if each child experiences events differently. They call these differences in how family members are treated ‘relative differences’.

Plomin and Thompson (1987) suggest that providing a child is brought up in a good enough, supportive, non-abusive or neglectful environment the actual family has little impact on the individuals personality or intellect (Gross, 2003). These different experiences within a family are called micro-environments – a very specific environment to that individual.

3. How we construct our environment

“Different people, at different developmental stages, interpret and act upon their environments in different ways that create different experiences for each person. In this view, human experiences are a construction of reality, not a property of a physical world that imparts the same experiences to everyone who encounters it” (Gross, 2003).

Scarr (1992) proposed that nothing is real; realities are the product of how things get represented and reacted to. What this means is that how we perceive events, how we understand what is happening around us, makes us see the world in a particular way.

Consider the following:

What is real? A beer glass is full or half empty

You start a new job – it’s challenging or it’s frightening

You win the lotto - £50 Yeah! Or, not so great?

4. Vulnerability

Horowitz (1987) developed a model of how an individual and their environment interact and how this can affect development. He believes a highly facilitative environment where the child has loving and responsive parents provides them with a rich, stimulating and facilitative upbringing. When different levels of facilitativeness are combined with a child’s initial vulnerabilities – there is an interaction effect.

For example a resilient child (i.e. one with many protective factors and a few vulnerabilities) may do quite well in a poor environment but a non-resilient child will only do well in a highly facilitative environment as in a poor environment they would suffer.

In support of this interactionist/vulnerability theory is the thirty year longitudinal study by Werner et al (1955). 700 children from Hawaii were followed from the ages of 2 yrs, 10yrs, 18yrs and 31-32yrs. Werner became interested in the number of children who despite problems in the early stages of development such as - pregnancy problems, general impoverished lifestyles, divorce, little education, alcoholic or mentally disturbed parents – still went on to develop healthy personalities, stable careers and strong interpersonal relationships.

As infants these resilient children were typically described as active, affectionate, cuddly, easy going and even tempered with no eating difficulties or sleeping habits that would distress their carers. These are all temperamental characteristics that elicit positive responses from both family members and strangers. There were also environmental differences between the resilient and non resilient children, such as smaller family size, at least 2 years between themselves and the next child, and close attachment to at least one carer (relative or babysitter).

How much do nature and nurture each contribute?

Jones ’93 cited in Gross 2003 suggests that nearly all inherited characteristics involve gene and environment acting together and it is impossible to sort them out into compartments. People see characteristics i.e. intelligence, as a ‘cake’ and then try to slice it to show how much gene and how much environment was involved. In fact the two are so closely blended that trying to separate them is more like trying to unbake the cake.

Schizophrenia and the nature nurture debate

The DSM IV criteria describes schizophrenia as having two or more of the following symptoms for 6 months + leading to a deterioration in social and work life.

• Hallucinations – mostly auditory

• Delusions – bizarre beliefs and thoughts about the world

• Disorganised speech

• Catatonic behaviour – repetitive movements or gestures

• Negative symptoms – flat, unresponsive

Using the handout – Explanatory theories of schizophrenia complete the table below:

|What evidence is there for nature? |What evidence is there for nurture? |

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Can we conclude schizophrenia is due to nature?

1. The concordance rate in all MZ studies are always less than ______% (_____% would be the rate if it was purely down to genes, therefore there must be other ____________ involved. For example____________________________________________________________________________________.

Finally twin studies often show a wide variation in results, e.g. Fisher (1973) found a concordance rate of only 24% in MZ twins reared apart.

|Other problems include? – think gene environment interaction |

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2. Schizophrenia is a name given to a group of disorders which may have quite different symptoms. Only some types of schizophrenia may have a genetic link.

3. By focusing on genetics, one can be criticised for adopting a _______________ approach. This is when we try and explain an aspect of human behaviour by looking at only ______ single factor and in this case ___________.

Perhaps it is better to utilise the __________ - __________ model which states that when considering why certain people develop schizophrenia, it is important that we do not only consider their ____________ vulnerability to a disorder (diathesis) but we must also consider ____________ stressors. Therefore if a person is biologically predisposed to develop the disorder if they have a good _____________ they will not do so.

Can we conclude that schizophrenia is due to nurture? NO!!!

Families are analysed _______________________ (looking back, long after mental disorders have surfaced); Faulty communication patterns may be the result of living with schizophrenia rather than the cause.

There is difficulty in explaining why schizophrenia develops in some but not all children within the _________ family as it is expected that communication systems would be similar between all members of the family.

Diathesis stress model - need to consider both ___________ and the ___________.

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