Rare mutations contribute to individual differences in personality and IQ.
Never has the nature vs. nurture question been more hotly debated than over the question of intelligence. To what degree are individual differences in IQ due to environment or heredity? Traditionally, the heritability of intelligence—the extent to which differences in intelligence are due to differences in genes—has been calculated by testing the intelligence of closely related individuals, such as twins, and comparing the results to tests of unrelated people. It has been much harder to examine the human genome directly in order to determine the extent to which genetic variation is associated with IQ differences.
However, our understanding of the genetics of intelligence is progressing quickly. Less than 10 years ago, a few studies had found gene variants associated with intelligence in certain population samples, but the results could not be replicated when the same tests were done on other populations. Today, on the basis of a survey of thousands of genes, we can assign someone a score that correlates moderately with performance on standardized tests which line up extremely well with IQ scores.
The genetics of personality has progressed less quickly than that of intelligence, but is also advancing, and a paper released this month takes us one step closer to solving two problems that still plague both fields.
First, there is the issue of “missing heritability.” This refers to a…