Critically Evaluate The Influences Of Nature And Nurture With Regard To The Concept Of Intelligence.

AS and A Level Psychology

Critically Evaluate The Influences Of Nature And Nurture With Regard To The Concept Of Intelligence

Stephen Hoyland

Furness College

Channelside

Barrow-in-Furness

Cumbria LA14 2PJ

Introduction

Is intelligence fixed, or is it shaped by factors in a person’s social environment? In other words, is it something that is set at conception as the product of breeding or is it something more complex linked to the overall function of the environment, or even a mixture of the two? The controversies surrounding the nature of human intelligence are long standing and have produced many varied studies.

According to the psychologists who lean towards the nativist (nature) idea of intelligence we are born with certain capacities to perceive our environment in certain ways, these capacities are often incomplete or immature when first born and develop gradually throughout childhood. These particular psychologists believe learning plays only a minor role in the development of an individual’s intellect.

The empiricists (nurture), on the other hand, maintain that we are born as blank slates and that our knowledge and abilities are acquired through a process of differing experiences and are therefore learned.

Theories of intelligence

The issue of the role of heredity or environment in shaping our eventual intelligence began to appear as long ago as the seventeenth century when a philosopher named John Locke (1632-1704) produced data on the subject of empiricism. Locke’s ‘tubula rasa’ or blank slate approach perceived that our minds are blank at birth and throughout our lives we combine external stimuli, forming chains of association, and as we mature these chains become more complex. This would give the individual the ability to perform single, complete units of interaction that were composed of many simple learned associations combined together.

This view differed from that of many philosophers of the time and also from the developing group of new psychologists. One such person who had very different ideas towards intelligence was Francis Galton, a committed eugenicist.

In his book Hereditary Genius (1884) he argued that from his studies of eminent Victorians intelligence clearly ran in the family and was therefore inherited. He went even further with his studies into inherited intelligence and behaviour and observed that the ‘lower classes’ were breeding at an alarming rate and to prevent the resulting lowering of intelligence these people should be prevented from breeding to keep the society racially ‘pure’ and prevent it from becoming ‘mongrelised’.

As the scientific study of intelligence continued to progress the introduction of standardized testing was introduced.

Alfred Binet developed the first recognised intelligent test in 1905. Binet reasoned that the age of a child had direct links to what could be expected in the way of intelligence development, e.g. a child of two could not be expected to recite the days of the week but it would be reasonable to expect this of a child of eight.

Binet, along with his colleague Theodore Simon, collected a series of such developmental tasks and produced a specific test, which matched these ...

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As the scientific study of intelligence continued to progress the introduction of standardized testing was introduced.

Binet, along with his colleague Theodore Simon, collected a series of such developmental tasks and produced a specific test, which matched these tasks to specific age groups. From this they devised a technique to evaluate the individual in question and place a single numerical figure on how they matched up to their peers, this became known as the intelligence quote or IQ.

The debate regarding the nature of intelligence expanded to include discussions about whether there is one specific factor in intelligence or perhaps two factors working in tandem. Spearman’s two-factor theory incorporates a ‘g’ factor or general ability and a ‘s’ factor or specific ability. Spearman performed something called factor analysis to try and determine the performance of children in a variety of differing tasks. These tasks were used to analyse, by score, the child’s ability in intelligence tests that might tap a varied range of abilities e.g spelling, arithmetic, punctuation, grammar and reasoning. The assumption is that the more similar the scores in two or more of these tests, i.e. the greater the correlation, the more likely the test are tapping the same ability e.g. the ‘general’ ability. But if some of the children do best on test one and worse on test two and another group of children vice-versa then it could be said that distinct abilities are being tested.

Research into the issues of intelligence

The nature-nurture issue in intelligence, along with the theoretical viewpoints, has allowed psychologists to carry out a wide and varied amount of research on this subject. This research has, as would be expected, thrown up a great deal of differing results which give weight to one side or other of the debate on the development of intelligence but in a growing number of cases actually show the combining of the two subjects, nature and nurture.

McGurk, (1975) stated that there are four intelligence related propositions that seem to lean towards the genetic theory, that is the belief that IQ differences are largely determined by genetic factors.

His first proposition related to genetic relationships between two individuals, the closer the genetic relationship the greater the concordance between them with respect to intelligence.

This proposition relates specifically to twins, monozygotic MZs, identical, and dizygotic DZs, non-identical.

Studies by Erlenmeyer-Kimling and Jarvik (1963) later updated by Bouchard and McGue (1981) seemed to support this proposition. However as the studies were conducted on MZs living together do they take into the account the possibilities of the twins’ environments also increasing in similarity as they increase in genetic similarity? In order to counter this problem the IQ of MZs reared separately would need to be compared to the IQ of MZs reared together.

The best-known Studies into MZs reared separately, Newman et al (1937), Burt (1955, 1958, 1966), Shields (1962) and Juel-Nielsen (1965), show that they are still more alike than DZs reared together suggesting a strong genetic link. Twin studies have, however, attracted a great deal of criticisms. This criticism related to the fact that the MZs classified as separated were in some instances not separated until the age of seven, eight or nine and in other cases were raised in related branches of the parents families and even attended the same schools. Taking these criticisms into account and with the improvements of research techniques we still find impressive correlations in the study of twins.

McGurk’s second proposition states that, as genetic inheritance is a constant, there should be a high degree of continuity in IQ throughout an individual’s lifespan.

To determine whether or not an individuals IQ has remained constant over time there is a need to calculate the stability coefficient. Honzik et al (1948) found in their studies of over 250 Californian children aged between 2 and 18, testing them at regular intervals, a strong correlation and very little fluctuation. However different research has produced a very different set of results, the Fels Longitudinal Study of Development (McCall, 1973) studied 140 middle-class children ranging in age from 2 ½ to 17 years old. This study showed an average change in IQ of 28 points and even in the case of the most ‘stable’ individuals a change, on average, of ten points was noticed; about 15% of the participants shifted 50 points or more, in either direction, and there was one increase of 74 points. Rebok (1987) warns that caution is needed when drawing conclusions in regard to later-life IQ from earlier data as intelligence is not as fixed as the original theories presumed.

His third proposition indicates that the IQ correlation between biological parents and their offspring should be stronger than any IQ correlation with adoptive parents.

Research into this third proposition needed comparisons to be made between the IQ correlation of children and their foster parents and the IQ correlation of children and their biological parents. Early studies by Burks, 1928 Leahy, 1935 and Skodak and Skeels 1949 did find correlation differences between children and their adopted parents and that of children and their biological parents, 0.15 between adoptive parents and adopted children and 0.48 between biological parents and their offspring. These studies were, however, criticised due to the way in which the two different family groups were matched; the adopted children came from families with a poor background and were being placed with families of a higher socio-economic status who had also been carefully screened by adoption agencies. Later studies (McGurk 1975) showed environment to have a marked effect on the level of IQ of the adopted children, the adopted environment raises the child’s IQ above what it probably would have been had the child remained with their biological parents. This study also came under debate when it was found if the environment remains constant between both adoptive and biological parents and children the IQ’s of the adopted children tended to be much nearer their biological parents (Schiff et al 1978).

The fourth proposition predicts that any attempt to deliberately increase or nurture the levels of intelligence should have little or no effect.

In the United States in the early 1960s there was a growing movement to try and close the educational gap between white middle class children and children from socially disadvantaged backgrounds. Two books that contributed to this movement, J McVicker Hunt’s Intelligence and Experience (1961) and Blooms Stability and Change in Human Characteristics (1964), both stated that intelligence was not a fixed attribute and intellectual ability could be increased by outside circumstances.

The first of these programmes introduced by the United States government was known as Operation Headstart. The programme aimed at pre-school children did show early increases in the children’s IQ but these increases were short-lived and the overall educational gains were shown to be minimal. This particular programme came under a lot of criticism, but after further study of the results it was shown that there was in fact a plateauing effect and there was improvements in the beneficiaries cognitive abilities (Brown and Grotberg 1981).

More recent studies on 111 Romanian children adopted into English families within the first two years of their lives (Rutter et al 1998), the children came from impoverished backgrounds suffering both psychologically and physically, compared to a sample of English adoptees showed a considerable catch up, both physically and cognitively, by the age of four years. This catch up was significantly improved if the adoption had taken place before the children were six months old.

Nature, Nurture or Both?

From the evidence produced in relation to the four propositions, which supported the genetic theory, it can be seen that the environment does play an important part in the development of intelligence. But how much? The balance between these two factors has produced conflicting results in its own right with Jensen (1969) claiming hereditability to be 80% whereas Bouchard and Segal (1988) said the figure was more likely to be around 50-60%. The differing research and study results documented do give an insight into perhaps how not only there is a need to have a positive environmental input but also the need to be aware of the actual effects hereditability has on the issue of intelligence.

The complexities of the nature and nurture positions could possibly suggest the need to perhaps reframe the debate on the nature of intelligence, perhaps a more useful question could be: how is intelligence influenced by both heredity and the environment? One possible response to this question was offered by Gardner (1983) who offered the multiple intelligence theory, stating that multiple intelligence is neutral on the issue of heritability, and emphasized the importance of environmental interactions. Although Gardner did not doubt that genetics do play an important part in intelligence, he stressed the interaction between genetic and environmental factors as pre-eminent.