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Intelligence is not just genetic02 November 2013, by Alexandra Gowling
The common opinion that one’s intelligence is due largely to genetic inheritance and cannot be improved has been shown to be incorrect.
Dutch researchers at VU University Amsterdam, the University of Amsterdam and Tilburg University have found that both a people’s genes and their environment play important roles.
They are proposing that the high heritability of intelligence stems from a dynamic interplay between genes and environment that occur throughout the course of a person’s development.
The interplay results in individual differences in knowledge and skills, from which differences in intelligence arise.
This is where education, culture and society comes in, as they enable genetic effects to arise. The greater the environmental influences, the greater the genetic effects.
Contradicting mainstream theories
In order to test mainstream theories, the researchers listed predictions from mainstream intelligence theories and then collected the results of thousands of intelligence test scores from all over the world.
The comparison showed that on essential aspects, the empirical results were the opposite of the predictions.
Knowledge that was culture-dependent, such as spelling and general knowledge, rated the highest among all abilities tested by intelligence tests, higher than less culture-dependent abilities such as memory, spatial ability and reasoning.
This does not follow mainstream theories of intelligence, in which intelligence is interpreted as a biological trait.
Nature vs. nurture
Scientists know that nature, as in genes, and nurture, as in environmental influences, both affect intelligence. Yet genes are generally considered to be more important, because in adulthood, individual differences in intelligence are about 80 per cent heritable. Therefore, as the theory went, the remaining 20 per cent must come from environmental influences.
Yet, as biological psychologist at VU University Kees-Jan Kan said, "Current theories of intelligence do not explain our findings."
"We need to get rid of the reasoning that because intelligence is highly heritable, it cannot really be moulded by environmental factors. This invalid reasoning has been pointed out before, but our research clearly indicates that empirical findings ask for a different interpretation of intelligence.
"Differences in vocabulary are the most heritable, but that does not imply that vocabulary is no changed by environment. Simply educate people in a different language or raise them in a different culture and their vocabulary develops radically differently."
The researchers concluded that there is a problem where heritability estimates have been based on a model in which genetic and environmental influences are independent from another, because those influences do go together.