Scientists have investigated this question for more than a century, and the answer is clear: the differences between people on intelligence tests are substantially the result of genetic differences.
Any one person’s intelligence might be blown off course from its genetic potential by, for example, an illness in childhood. Intelligence, more appropriately called general cognitive ability, reflects someone’s performance across a broad range of varying tests. Researchers are now looking for the genes that contribute to intelligence. Recent studies of hundreds of thousands of individuals have found genes that explain about 5 percent of the differences among people in intelligence.
Another particularly interesting recent finding is that the genetic influence on measured intelligence appears to increase over time, from about 20 percent in infancy to 40 percent in childhood to 60 percent in adulthood.
Scientists might use DNA to try to map out the developmental pathways linking genes, intelligence, the brain and the mind.