Nature versus Nurture in Intelligence

1. The upper level link of this information: Intelligence & Psychological Testing (An undergraduate psychology course about Individual Differences)

2. This source: Natrue versus Nurture in Intelligence

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Nature vs Nurture in Intelligence

Last updated: 10 Apr 2005

Overview Nature vs. Nurture - What do you think? Pendulum of opinion on Nature vs. Nurture through history Historical trends in the nature-nurture debate Evidence in favour of “nature” Evidence in favour of “nurture” The role of “interaction” What have we learnt about intelligence? Final quotes References

Overview The issue of what causes individual differences in intelligence goes beyond psychology, and involves moral, political, ethical, educational, social, physiological and statistical issues to name just a few. The issue of how differences in intelligence come about between individuals and groups is a topic of much fascination and controversy - it can arouse strong reactions and elicit personal beliefs and biases. This page outlines some of the main psychological concepts and evidence that relates to explaining individual differences in intelligence. As a student, it is your responsibility to develop a familiarity with the basic arguments, strengths, and weaknesses for and against the causal influences and correlates of intelligence.

Nature vs Nurture - What do you think? In looking for the causes of individual differences in intelligence, a major issue is the relative contribution of genetics and environment. 100% Genetics (Nature) 90% Gen. 80% Gen. 70% Gen. 60% Gen. 50-50 60% Env. 70% Env. 80% Env. 90% Env. 100% Environ. (Nurture) Rate the extent to which you believe nature and nature influence (cause) human intelligence. Warning! As you learn more about the theory and research on genetic and environmental influences on human intelligence, you may find that you change some of your beliefs and assumptions.

Pendulum of opinion on Nature vs. Nurture through history The zeitgeist (the intellectual and culture "flavor" of a time and place) has swung back and forth over time with regard to the amount of influence that nature vs. nature has on human intelligence. For example, in the late 1800's in the UK, as Darwinism took off, the role of genetically determined capability was considered very important. This was in constrast, for example, to the 1960's in the USA, when views were more in favor a "tabula rasa" (blank state) view of human intelligence - in other words, all people are capable of much more, if given conducive environmental conditions in which to reach their potential Currently the Zeitgeist is the Western psychological world is somewhere inbetween - both genetics and environment are seen as playing important roles. To be more precise, the modern view about nature vs nurture in intelligence is "interactionist". This view is well expressed by Ridley (1999, p.77): "Mother Nature has plainly not entrusted the determination of our intellectual capacities to the blind fate of a gene or genes; she gave us parents, learning, language, culture and education to program ourselves with."

Historical trends in the nature-nurture debate Late 19th century - early 20th century (Nature) From the mid to late 1800's through to the early 1900's opinions rested in the nature camp. This was consistent with the scientific discoveries of the role of inheritance and natural selection by Mendel and Darwin. The major contributor to the psychological argument was Francis Galton in his book "Hereditary Genius: Its Laws and Consequences” (1869). Galton had observed that the gifted individuals tended to come from families which had other gifted individuals. He went on to analyze biographical dictionaries and encyclopedias, and became convinced that talent in science, the professions, and the arts, ran in families. Galton took this observation one step further, to argue that it would be "quite practicable to produce a high gifted race of men by judicious marriages during several consecutive generations". This suggestion became know as eugenics, "the study of the agencies under social control that may improve or repair the racial qualities of future generations, either physically or mentally." Galton wanted to speed up the process of natural selection, stating that: "What Nature does blindly, slowly, and ruthlessly, man may do providently, quickly, and kindly”. Galton was convinced that "intelligence must be bred, not trained". Such arguments have had massive social consequences and have been used to support apartheid policies, sterilization programs, and other acts of withholding basic human rights from minority groups. Post WWI: 1920’s-1930’s After World War I, careful reanalysis of the mass of intelligence test data took place. This began to challenge the commonly held view that intelligence was directly, genetically linked to racial differences: e.g. blacks from Illinois had higher IQ scores than whites from 9 southern states - a finding difficult to reconcile with the simple idea that whites are intellectually superior to blacks. Evidence now seemed to support a closer link between social class and intelligence, rather than race and intelligence. As a result, a number of psychologists in the 1920s and 1930s shifted their position towards the environmental camp. The shift against 'nature' views was given momentum by the backlash against the social consequences of government policies: e.g. sterilization laws had been passed in 24 US States, resulting in 20, 000 people being sterilized against their will. 320, 000 people suffered the same fate in Germany. 1940’s-1990’s The backlash faded, and the pendulum swung back towards the middle. From the early 1940's, it seemed there was a rejection of simplistic nature or nurture views, with more common recognition of their complex interplay. Nevertheless, social prejudices and inequalities were still evident and growing. Thus, in the 1960's, the focus of the problem was shifted away from the individual as the cause of the problem, and centered on social determinants. Thhe pendulum swung towards the nurture/environmental end and away from the nature/genetic end. Efforts were made to arrest poor educational achievement through special schooling, and to alleviate poor living conditions through welfare. It became politically correct to minimize talk and discussion of the role of 'nature' in contributing to any individual differences, let alone intelligence. The evidence of differences in intelligence between socioeconomic groups and racial groups, however, did not go away. Recent trends – "The Bell Curve" controversy From time to time, there have been inflammatory articles which present and interpret evidence of IQ differences between groups (in particular Jensen, 1969). The most recent, and most major of these publications was Herrnstein and Murray's (1994) "The Bell Curve". This book provided momentum to swing the pendulum in the direction of 'nature', at least in the public's eye, but even more so, it generated massive debate and controversy in psychology, sociology, education, and politics, not to mention the media and household. The 800+ page book, written for laypersons, hit the best-seller lists in the U.S. "The work's main thesis is that an individual's intelligence - no less than 40% and no more than 80% of which is inherited genetically from his or her parents - has more effect than socioeconomic background on future life experiences." Manolakes (1997), p.235 In addition to the premise that measured intelligence (IQ) is largely genetically inherited, a second important premise was that IQ is correlated positively with a variety of measures of socioeconomic success in society, such as a prestigious job, high annual income, and high educational attainment; and is inversely correlated with criminality and other measures of social failure. It was suggested that SES successes (and failures) are largely genetically caused. Some sample controversial quotes from "The Bell Curve" “IQ has more effect on future life experiences than SES” “intervention efforts are largely a waste of time and money” “increasing population of 'lower caste' intelligences, lessening the nation's 'genetic capital” Reactions to The Bell Curve: The Bell Curve" re-ignited the nature-nurture debate. The public debate was (and is) divided. The politically left saw the authors as "un-American”;- "pseudo-scientific racists”;- and the book as "alien and repellent" The politically right saw the authors as: - "brave and respectable scholars,”;- whose book was "lucid" and "powerfully written" The part of The Bell Curve that captured public attention was on the differences in IQ between African and Caucasian Americans. Further to this were the suggestions made by Herrnstein and Murray about the implications of a predominantly genetically-inherited intelligence for public and social policy. Since IQ was largely seen as genetically determined, the authors expressed resistance to educational and environmental interventions. They argued that money spent in this way is wasted. The authors also argued that America is becoming a society of 'cognitive castes', with the lower caste including a large proportion of African-Americans. Hence their statement that the 'genetic capital' of society is being eroded because the less intelligence, lower class is reproducing at a greater rate than high IQ classes.