One finding of this technique, which is known as genome-wide complex-trait analysis, is that many of the same genetic factors seem to explain why people differ in intelligence in childhood and old age.

WSJ: Intelligence Changes Linked to Genes

Another finding is that people tend to retain a similar "rank order" in intelligence level between childhood and old age.

WSJ: Intelligence Changes Linked to Genes

The new study, published in the journal Nature, offers one of the first estimates of how much genes and the environment contribute to fluctuations in a person's intelligence between adolescence and old age.

WSJ: Intelligence Changes Linked to Genes