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Intelligence: Heredity-Environment Debate Resolved?

According to neuro and cognitive scientists, different intellectual abilities are based on neural circuits that require environmental stimulation for development -- and are open to change.

However, intelligence researchers argue that there is a general factor of intelligence ("G") that is highly heritable and defines intelligence as an overall innate ability to perform well on different measures of intelligence -- which are not open to change.

This debate is reviewed in an analysis of 124 studies of the underlying basis of intelligence in the January issue of Psychological Review published by the American Psychological Association.

Psychologist Dennis Garlick, Ph.D., of the University of Sydney in Australia, submits that the neural plasticity model of intelligence better explains how intelligence is developed. This model suggests that intelligence is created when neural connections in the brain are changed in response to environmental cues.

According to Garlick, recent advances in neuroscience and cognitive science have suggested that different intellectual abilities require different neural connections in the brain and that the only mechanism that allows the brain to grow such connections would be an adaptation mechanism that responds to environmental input.

Should the general measure of intelligence ("G") be discarded? Not necessarily, says the author. These findings are not inconsistent with the notion of a general measure of intelligence and may in fact provide a foundation for such a general measure because if people differ in their ability to adapt their neural connections in response to the environment, a general factor of intelligence would result.

According to Garlick, reasoning capacities are a function of the connections of the neural system, connections that develop during childhood as the neural system adapts to the environment. However, Garlick also notes that the capacity of the nervous system to change the connections in response to environmental cues stops at maturity. This corresponds to the observation that reasoning capacities are observed to no longer increase after time.

Does one have to be a child Einstein to be an adult Einstein? Yes, if the developing brain has the ability to make the right connections, according to this theory.

"You could present a person with an IQ of 200 with the appropriate phenomena when they are 20 years old, after the critical learning period, and they would not have the capacity to adapt their brains to the new phenomena," Garlick writes. "This is also used to explain why children can learn other things easier as well, such as language."

"The issue of the cause of intelligence has been one of the great controversies of modern psychology, with a fierce debate between two opposing camps," said Garlick. "Those who argue for environmental factors and those who argue for innate factors. The model described in the paper provides a resolution to the debate and shows that both sides have been seen, at least partially, correct. It also allows recent advances in the neuro and cognitive sciences to increase our understanding of human intelligence."

The author suggests that the neural plasticity model can be applied to improving the educational outcome of underachieving children. Garlick's analysis suggests that people of low IQ perform poorly because their brains do not adapt well to environmental stimulation.

Educational methods could therefore be designed to help produce the appropriate changes in the neural connections that are necessary for learning. These designs should be guided by work on artificial neural systems that has shown that networks with low learning rates are more likely to successfully master a problem when the complexity between input and output is reduced and the network is taught in stages.

(Reference: "Understanding the Nature of the General Factor of Intelligence: The Role of Individual Differences in Neural Plasticity as an Explanatory Mechanism," Dennis Garlick, Ph.D., University of Sydney, Australia; Psychological Review, Vol 109, No. 1.)

(Editor's Note: Full text of the article will be available at this URL after January 31.)

[Contact: Dennis Garlick PhD, Pam Willenz]






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