When it comes to smarts, which is more important — nature or nurture, genetics or environment? Well, yes, it seems. New findings now suggest that half of all differences in intelligence between people appear rooted in the collective influence of many tiny genetic variations. That leaves plenty of influence open to other factors, the researchers said.
Past research had suggested that bright parents tend to have bright kids. However, the extent to which genetics contributes to intelligence, as opposed to other contributing factors such as environment, has been hotly debated.
No single gene variant has yet been identified as reliably linked with intelligence. Instead, scientists investigated the potential role of many common genetic variations on human intelligence.
A gene is a string of molecules known as nucleotides, much as a word is a sequence of letters. The recipe of nucleotides making up each gene is not always precise — for instance, the copy of a gene a person has might differ by one nucleotide from the copy of that same gene seen in someone else, much as the word "cat" differs from "car" by a single letter.
Researchers compared nearly 550,000 of these variations, known as single nucleotide polymorphisms (SNPs, or "snips") with the performance of more than 3,500 unrelated adults on a pair of tests of general intelligence — one on problem-solving skills, the other on acquired knowledge, such as vocabulary. Genetic variations could explain about half of all the differences seen in intelligence between people — that is, some combinations of these variants seem show up more in smart people.
"We have found gene signals associated with cognitive abilities," researcher Ian Deary, a psychologist at the University of Edinburgh in Scotland, told LiveScience.
Although the researchers found that genetic variations can affect intelligence, they cautioned they do not yet know which genes are important, or how much each contributes. "The likelihood is that there are very many genes contributing, each with a small effect," Deary predicted.
In addition, while the scientists focused on genetic contributions to intelligence, Deary cautioned their results also show "that the environment is important too."
"We are not saying that intelligence is 'fixed' or 'determined' in our genes," researcher Peter Visscher, a quantitative geneticist at the Queensland Institute of Medical Research in Australia, told LiveScience. "We are saying that about 50 percent of individual differences between people in intelligence is due to genetics. We are not saying that the environment is unimportant."
Future research could not only investigate what specific genes seem linked with intelligence, but how they might interact with the environment, as well as how these genes impact changes in cognitive skills with age Deary added. "We want to use these data to find out why some people's thinking skills age better than others," Deary said.
The scientists detailed their findings online Aug. 9 in the journal Molecular Psychiatry.