The idea of intelligence being genetically inherited jars a lot of smart people.
The Smarts among us like to imagine they are largely responsible for creating their own intelligence, perhaps with the help of caring parents and experienced teachers. And parents tend to over-estimate the contribution their own activities make in increasing the intelligence of their children.
For a long, long time, however, twin studies have shown that around half of intelligence is genetically inherited. And now a new study published on Tuesday in the journal Molecular Psychiatry establishes this without a doubt.
"It has been getting clearer and clearer that any genetic contribution to traits on which people differ—like height and weight—comes about from large numbers of gene differences, each with very small effects," said Prof Ian Deary of the University of Edinburgh, who led the research on intelligence. "We thought that was one possibility for cognitive ability differences, and our results are compatible with that."
To test his idea, researchers looked at more than half a million locations in the genetic code of 3,511 unrelated adults. Each of these sites is where people are known to have single-letter variations in their DNA, called single nucleotide polymorphisms (SNPs). These variations were correlated with the individuals' performance in two types of psychometric tests that are established in assessing intelligence: one test measuring recalled knowledge (via vocabulary) and the second measuring problem-solving skills.
They found that 40% of the variation in knowledge (called "crystallised intelligence" by the researchers) and 51% of the variation in problem-solving skills ("fluid-type intelligence") between individuals could be accounted for by the differences in DNA.
The results are published on Tuesday in the journal Molecular Psychiatry.
Of course, this doesn't mean that having caring parents, good teachers and working hard doesn't matter. They probably do matter. But just not as much as a lot of people think.
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