Nature versus nurture: it's one of the great debates in human society. Are we the product of our environment, or does our genetic make-up determine how we turn out? A new study published in the journal 'Nature' suggests that nearly a quarter of the changes in a person's intelligence level over the course of a lifetime may be due to genes, rather than environmental factors.
According to S. Duke Han, an assistant professor in the department of behavioural sciences and a clinical neuropsychologist at Rush University Medical Center in Chicago, the study is unique and revealing: "What this is saying is something many researchers have accepted for a long time, that intelligence seems to be very much influenced by genetic makeup but also environmental factors," Han said.
Usually studies like this have to rely on comparisons between people who are related, such as identical or fraternal twins. This study is different. It uses information from a Scottish database containing intelligence tests from a group of unrelated people, first at age 11, then at 65, 70 or 79, and therefore allows the researchers to compare people who are not related by blood at early and late stages in their lives. Participants also shared DNA samples so that researchers could examine their genetics.
The findings were interesting: people with similar DNA tended to have similar changes in intelligence from youth to age. Also, many people who scored high on the test at age 11 also did so when they re-took the test later in life - although not everyone. Ian Deary, lead author of the study, told the Wall Street Journal that although it lacks statistical power in some crucial aspects, the study is valuable because "it is very rare to have an estimate of the genetic contribution to lifetime cognitive change." He also clarified, "these results suggest that genes contribute to our understanding of why some people's brains have aged better than others, but the environment is probably the larger influence on lifetime changes," Deary said.
Other studies have found that a person's intelligence level, as measured by an IQ test, isn't fixed at birth. In fact, a person's IQ can rise or fall as the person ages - a teenagers IQ can increase or decline by as many as 20 points in only a few years. And scientists have made progress in figuring out which environmental factors may affect intelligence. Some cognitive training has shown to increase IQ scores after just a few weeks, although the increases are small and tend to fade after a few months.
This is not the first time scientists and thinkers have investigated the relationship between intelligence and genetics. Here are some other articles on the subject:
AllPsych Journal: 'I.Q. - Genetics or Environment'
Discover Magazine: 'When genes matter for intelligence'
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