Imagine you have two identical twins, who have been separated at birth and offered for adoption. One is taken to the home of a university scientist, who is able to pay for private education and tutoring as the child grows up. The home itself is a stimulating environment and she is offered every chance to stretch her mind.
Her sister, in contrast, grows up in a less well-off and less bookish household, and attends a struggling state school. She is happy and well-looked after, but overall her family have less resources for her continuing education.
Once they reach 18, the twins are both given an IQ test. Which sister would have the higher score?
Examining the fates of adopted siblings is just one of the ways that scientists can examine the factors influencing intelligence. They can also compare non-identical twins to regular siblings and strangers, for instance, to pick about the role of genes and the environment.
But no matter what technique they use, these studies all point to the same answer. By the time we reach adulthood, between 60 and 80% of the variation in IQ scores can be explained by our genes. And that is reflected in the brain’s anatomy: our genes can decide the strength of the connections between different neural regions, which then determines how quickly the brain can process information.
Although IQ does seem to predict our success at school, psychologists are now coming to realise that those tests may neglect many skills that are crucial in other areas of life.
All of which would seem to suggest that our intelligence (or at least, our potential to cultivate intelligent thinking) is largely determined before we are born. In reality, those differences may not be as meaningful as we once thought. For one thing, the IQ score examines just a narrow band of verbal, abstract reasoning and memory skills. Even the man who invented an early version of the test, Alfred Binet, warned against the "brutal pessimism" of using these tests to predict a child's fate later in life. Binet wanted to use his test to identify which children might need extra help at school – not to define their life’s achievements.
Although IQ does seem to predict our success at school, psychologists are now coming to realise that those tests may neglect many skills that are crucial in other areas of life. The psychologist Robert Sternberg at Cornell University, for instance, has examined forms of “practical” and “creative” intelligence that seem to bear little relation to traditional academic measures of success. This includes the ability to pick up “tacit knowledge” in the workplace, including the ability to manage other people, and “counter-factual thinking” – our capacity to think of alternative solutions to a problem. Crucially, these skills come from experience rather than a genetic gift.
There seems no doubt that some people will be born with certain predispositions and natural aptitudes, but whatever brain we end up with, we all have the capacity to improve the way we use it.
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Read more from David Robson here.