The Nature-Nurture Debate - Article Example

The nature/nurture debate in intelligence Introduction This paper will examine the nature-nurture debate regarding the development of human intelligence. This topic has interested psychologists ever since the concept of intelligence was formalised and measurements of intelligence were devised. In this context, ‘nature’ refers to people’s innate, inherited or genetic potential, while ‘nurture’ refers to the influence of the social environment, education, culture and so on. The paper outlines the history of the field of intelligence testing and theory, and the contributions of individual psychologists are described and assessed. The current situation regarding the nature-nurture debate is mentioned, and an attempt will be made to show that both nature and nurture are important in the development of intelligence. The interaction between nature and nurture is what counts, and it is impossible to prove that either one is more important than the other. Construct measurement Intelligence is a construct, and constructs are abstract ideas which are used to explain an observed phenomenon (Rosenthal & Rosnow, 1991). A child who scores well on both mathematics and English tests might be inferred to have a high intelligence, based on the available evidence. However, intelligence, like any other construct, is not directly observable, as are physical qualities such as height, weight or hair colour. This means that whatever is being measured is not necessarily the construct in question (Rosenthal & Rosnow, 1991). It is possible that the test is assessing the child’s education rather than intelligence, or a combination of both. The history of the concept of intelligence Sir Francis Galton was the first scholar to suggest that intelligence is hereditary. His personal life probably shaped his viewpoint, since he was born into an affluent family and Charles Darwin was one of his cousins (Weiten, 1989; Bulmer, 2003). Galton studied family trees and saw that eminence and success seemed to run across generations within the same families. In 1869 Galton published the theory that this success was due to genetic superiority. However, what he failed to acknowledge was that these families were usually the wealthiest ones, where individuals were very well-educated and enjoyed social influence (Weiten, 1989). Galton conducted twin studies, using both genetically similar (identical) twins and non-identical twins, to tease out the influence of nature versus nurture (Bulmer, 2003). Galton became convinced that nature (genes) was the stronger of the two influences. He was so sure of his theory of genetic superiority that he went on to build the concept of eugenics, where he envisaged that only genetically ‘superior’ people should marry and breed, thus eventually improving the quality of the entire human race (Weiten, 1989). These days, eugenics are associated in many people’s minds with the Nazi atrocities of World War II, where Jews, disabled and intellectually handicapped people and other groups whom the Nazis deemed to be genetically inferior were ruthlessly exterminated on a mass basis. Galton also theorised that higher intelligence would be associated with superior sensory reaction times. He carried out research to test this hypothesis, and found that it was not true. These experiments had an unexpected spin-off in that they led Galton to develop the idea of statistical correlation, and showed that measuring mental ability might be possible (Weiten, 1989). Galton was also a pioneer in studying normal distributions (Bulmer, 2003), in which most members of a population possess an average amount of a trait or ability, with few people possessing either above- or below-average amounts (Rosenthal & Rosnow, 1991). Darwin himself did not agree with Galton’s ideas about the genetic superiority of some families, or with the principles of eugenics. But a new school of thinking emerged which was known as ‘Social Darwinism’, with Herbert Spencer as its main proponent (Hofstadter, 1941). Social Darwinism posited that the laws of the survival of the fittest, as described by Darwin with reference purely to plants and animals, apply for humans too. John Stuart Mill, a prominent philosopher, disagreed with Social Darwinism and argued that the environment exerts a greater influence than hereditary factors, and therefore no human being should be deprived economically and politically (Mill, 1991). Alfred Binet was influenced by Mill, and he was also influenced by Jean-Martin Charcot, another ‘hereditarianist’ (Indiana.edu). Binet furthered Galton’s work with intelligence testing, and in 1904 he was commissioned to create a test to identify intellectually handicapped children who would not benefit from mainstream education (Weiten, 1989). Unlike Galton, who had emphasised sensory acuity, Binet assumed that verbal reasoning ability and the ability to manipulate information were the best markers of intelligence. A child’s score was expressed in ‘mental age’. In 1905 Binet and Simon published an intelligence test which had good validity in that it predicted school success fairly well. It was soon in use across Europe and America. Binet revised the test twice before his death in 1911, and thereafter other psychologists continued with his work, notably Terman and Wechsler in the USA (Weiten, 1989). Wechsler developed adult intelligence tests (Weiten, 1989). Terman’s team at Stanford University modified Binet’s test and in 1916 the Stanford-Binet Intelligence Scale was published. Instead of giving a mental age, it yielded an intelligence quotient or IQ, calculated by dividing the mental age by the chronological age and multiplying by 100 (Weiten, 1989). This test became famous, and has long been the golden standard for assessing new intelligence tests. Like Galton, Terman felt that intelligence was largely inherited, and he researched gifted children (Weiten, 1989). Thus it can be seen that adherents of both the ‘nature’ and ‘nurture’ positions have made valuable contributions to the field of intelligence research. Robert Yerkes was an American psychologist who was influenced by Darwinism, although he was not a strict Social Darwinist, since he felt that eugenic engineering was necessary to improve the human race (Indiana.edu). In 1917, as president of the American Psychological Association (APA), Yerkes helped to develop screening instruments that were used to assess World War I soldiers. Terman was also involved in developing these tests (Indiana.edu). The Army Alpha was based on Binet’s tests in a modified form for adults, while the Army Beta was a non-verbal test that was used for illiterate men or non-English speakers (Indiana.edu; Sundberg, Taplin & Tyler, 1983). The final versions of the Army Alpha and Beta were published in early 1919, and by the end of the war they had been used to assess about 2 million men (Indiana.edu). The Army Alpha and Beta tests were a milestone for psychology, as this was the first time group intelligence tests were used, and the testing also raised public awareness and acceptance of psychometric testing. But the data began to highlight issues of racial difference in scores (Indiana.edu). Personality assessments, and Woodworth’s psychiatric screening test for army recruits, were also developed at this time (Weiten, 1989; Sundberg et al., 1983), and the nature-nurture debate spread to this field too. The view of intelligence and ability as fixed, inherited traits would never again go unchallenged. Charles Spearman was the next influential intelligence researcher, and he developed a theory which allowed for specific domains of intelligence as well as general core ability. He named the specific domains S1, S2, S3 and so on, with general ability being labelled ‘g’ (Weiten, 1989). Spearman made use of factor analysis, a statistical technique that analyses the relationships and clustering between the scores of numerous variables (Rosenthal & Rosnow, 1991). In the 1940s, L.L Thurstone built on Spearman’s theory but argued that there was far too much emphasis on g. He posited seven primary mental abilities, with potentially uneven distributions within one individual (Weiten, 1989). J.P Guilford followed this line of thinking and did away with the concept of g altogether, and divided intelligence in 150 separate abilities (Weiten, 1989). These theories attracted interest and support, but did not alter the nature of intelligence testing much, which continued to focus on assessing g. They also did not shed much light on the nature-nurture question, since they attempted to measure intelligence but did not explain how it had developed. In the mid twentieth century there was a case of fraudulent research in the field of intelligence testing. The fraudster was Sir Cyril Burt, who favoured Galton’s view of inherited intelligence (Weiten, 1989). Burt felt that impoverished people should be prevented ‘from propagating their species’ (Burt, cited in Weiten, p. 322), and his approach influenced British educational policy, which excluded the underprivileged classes from higher education. When critics began to question this approach, Burt fabricated and published the results of 53 twin studies in which he claimed to show that identical twins reared in different environments remained very highly correlated in their IQ scores; he reported a correlation of 0.88 (i.e. 88%). These bogus results were similar to the results of other legitimate researchers but the correlation was exaggerated. Burt’s fraud was only discovered after his death in the 1970s (Weiten, 1989), and it shows how strongly some psychologists feel about the nature-nurture question and the lengths to which they will go to defend their position. By now it was clear that both genes and environment (nature and nurture) shape IQ, and there was also no doubt about the fact that different racial or cultural groups do score differently. What was not yet clear was why these differences existed, and how much was due to cultural factors or educational disadvantage. In 1969 Arthur Jensen put forward the controversial argument that 80% of IQ differences result from genetic rather than cultural differences, with whites being superior in intelligence (Weiten, 19089). His mentor was Hans Eysenck, who also believed that intelligence had genetic determinants, although by the time Eysenck wrote his autobiography in 1990 he conceded that environment did also play a role (Indiana. Edu). Jensen’s 80% estimate was based on studies which were dominated by white subjects, which makes them questionable (Weiten, 1989). Leon Kamin, who was the first person to uncover Burt’s fraudulent data, argued that even if the genetic factor in intelligence is high, the differences in IQ scores between whites and blacks could still be due to environmental influences (Weiten, 1989). He used the analogy of two sacks which are filled with the same kind of corn seed, with naturally occurring variations in the quality of the individual seeds. One of the sacks is emptied over a fertile field and the other over a barren field. Naturally, the corn that grows in the barren field will be inferior, even though the original seed is of the same general quality in the two sacks. In both the fertile and barren fields, which represent the influence of the environment, there will be a range in the quality of the individual plants, which represents the influence of genes (Weiten, 1989). Jane Mecer similarly argued that IQ tests measure both mental ability and assimilation into the mainstream culture (Weiten, 1989). Currently, intelligence research is focusing more on cognitive processes rather than on presumably fixed traits. Less emphasis is placed on IQ tests today than previously, with achievement or outcome-based tests often being preferred. Robert Sternberg has proposed a widely used cognitive model for understanding intelligence, in which knowledge acquisition is seen as important (Weiten, 1989). Conclusion The heatedness of the debate and instances such as Burt’s fraud indicate how much is at stake regarding intelligence. Those who believe that intelligence is inherited are usually members of affluent and educated classes, such as Sirs Galton and Burt, who may fear that sharing resources with the masses would not be to their own or their families’ advantage. If they can prove that enriching the education of underprivileged children would not improve those children’s IQ, they would be happy to do so. In contrast, those who believe that everyone should be given a fair chance in life are likely to consider themselves morally correct, and what is at stake for them is their own moral conscience and the desire to uplift humanity. These people are likely to argue that intelligence is not genetic but depends on a good education. It is easy enough to see how both sides of this debate could be quite firmly opposed to the opposite viewpoint. Regarding the interaction between heredity and environmental influences, the debate continues, but there is general consensus that both are important. Numerous twin studies, enrichment and deprivation studies, and multicultural educational research testify to this fact (Weiten, 1989). What is not yet fully understood is exactly how heredity and environment interact to shape intelligence. One theory, known as the reaction-range model, suggests that while genes set a range within which an individual may develop, the environment determines one’s specific placement in this range—in other words whether one’s ability falls at the upper or lower end of the range (Weiten, 1989). However, there is no way to measure this genetically determined range, as it is a construct. This leaves the debate about the precise input of ‘nature’ versus ‘nurture’ unresolved. We cannot say that either the environmentalists or the hereditarianists got it right, or got it wrong, as both views have merit. The only uncertainty that remains is the exact proportion of each influence, and whether or how much that proportion can vary across individuals. References Bulmer, M.(2003). Francis Galton: Pioneer of Heredity and Biometry, Johns Hopkins University Press Hofstadter, Richard. William Graham Sumner, Social Darwinist The New England Quarterly, Vol. 14, No. 3. (Sep., 1941), pp. 457-477. Indiana University website, biographies accessed from at ‘Human Intelligence: biographical profiles’ on 12 January 2008: http://www.indiana.edu/~intell/yerkes.shtml http://www.indiana.edu/~intell/binet.shtml http://www.indiana.edu/~intell/eysenck.shtml http://www.indiana.edu/~intell/terman.shtml http://www.indiana.edu/~intell/charcot.shtml Mill, J.S. (1991) “On Liberty” J.S. Mill - On Liberty in Focus. (eds.) Gray J. & G.W. Smith. London: Routledge. Rosenthal, R. & Rosnow, R.L. (1991). Essentials of behavioral research: methods and data analysis (2nd ed). USA: McGraw Hill Sundberg, N.D., Taplin, J.R.& Tyler, L.E. (1983) Introduction to Clinical Psychology. New Jersey: Prentice-Hall Weiten, W. (1989). Psychology: Themes and variations. 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