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  » Types of Intelligence

  » Intelligence, Heredity, and Environment
        Evidence for Nature
        Evidence for Nurture
        Comments on Research

  » Neuropsychological Testing
        Normal Intelligence
        Abnormal Examination             and Brain Trauma

  » Spectroscopy Data

  » Disorders related to Intelligence

  »  Gender Differences
       Self-Estimated              Intelligence
       Anatomical Differences
       Gray vs. White Matter

  » Artificial Intelligence
        A Timeline of AI
        Ancient History of AI
        Modern History of AI
        The Future of AI

  » Age and Intelligence
        Areas of Function
        Effects of Lesions

  » References

Historical Trends in the Nature vs. Nurture Debate

Late 19th century - early 20th century (Nature)

From the mid to late 1800's through to the early 1900's opinions favored the nature camp. This was consistent with the scientific discoveries of the role of inheritance and natural selection by Mendel and Darwin. As we saw, the major contributor to the psychological argument of intelligence was Francis Galton with his book "Hereditary Genius: Its Laws and Consequences” (1869).

Primarily, 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, influenced by his research and findings, took this observation one step further and argued that it would be "quite practicable to produce a high gifted race of men by judicious marriages during several consecutive generations". (Bynum, 2002) Today, this suggestion is known as eugenics, which is defined by scientific dictionaries as, ‘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”. (Bynum, 2002)

After World War I: 1920s-1930s

After World War I, careful reanalysis of the mass of intelligence test data took place. This new research began to challenge the commonly held view that intelligence was genetically linked to racial differences. Evidence now seemed to support a closer link between social class and intelligence, rather than race and intelligence. This caused a shift of the ‘dominant’ opinion towards the ‘nurture’ camp, and as a result, a great number of psychologists in the 1920s and 1930s changed sides, becoming environmentalists about ‘intelligence’.


The reaction in the favor of environmental factors affecting intelligence faded shortly, and common belief shifted 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 interaction.

In fact, during 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. The dominant side was once again the nurture/environmental camp. Efforts were made to stop poor educational achievement through special schooling, and to diminish poor living conditions through welfare, because it was thought that intelligence and mental abilities were almost solely determined by the learning individuals acquire from their environment.

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.


Nature vs. Nurture Debate: Contemporary Literature

From time to time, there have been inflammatory articles which present and interpret evidence of IQ differences between groups, and today we all come across such articles in science magazines. The most recent, and most major of these publications was Herrnstein and Murray's "The Bell Curve" (1994). This book provided momentum in favor of the 'nature' side, at least in the public's eye, but even more so, it generated massive debate and controversy in psychology, sociology, education, and politics. 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.

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 socioeconomic successes (and failures) are also largely genetically caused. In a nutshell, this work of Herrnstein and Murray supported a somewhat hereditarian explanation of intelligence and definitely influenced many contemporary experts to shift their opinions toward the nature side of the argument.