Individual and cultural differences in intelligence

The essentials

Intelligence is shaped by both heredity and environment. Twin studies show that identical twins reared together have more similar intelligence scores than fraternal twins, pointing to genetic influence, while adopted children and children moved to enriched environments show gains, pointing to environmental influence. The current view is that intelligence results from a complex interaction of the two.

IQ scores in a large population follow a normal (bell-shaped) distribution with a mean of 100 and a standard deviation of about 15. Most people score between 90 and 110.

Key points

• IQ classification: above 130 very superior; 120–130 superior; 110–119 high average; 90–109 average; 80–89 low average; 70–79 borderline; below 70 intellectually disabled.
• About 2 per cent of people score above 130 and about 2 per cent below 70.
• Intellectual disability involves significantly below-average intellectual functioning together with deficits in adaptive behaviour, appearing during the developmental period (before 18 years).
• Giftedness is exceptional general ability shown in superior performance; talent refers to remarkable ability in a specific field.
• Culture provides the context in which intelligence develops. Western societies tend to value technological intelligence (attention, observation, analysis, speed, achievement orientation).
• The Indian view is closer to integral intelligence, giving importance to connection with the social and natural environment. The Indian concept of buddhi includes cognitive, social, emotional and entrepreneurial competence.
• Culture-fair tests try to reduce cultural bias, for example by using non-verbal tasks such as Raven's Progressive Matrices.

Exam tips

• Remember the four competencies of the Indian notion of intelligence and examples of each.
• Know that verbal tests favour children from the culture in which the test was made.

Common mistakes

• Assuming IQ alone defines intellectual disability; adaptive behaviour deficits must also be present.
• Thinking a culture-fair test is completely free of cultural influence; it only reduces such bias.