Dr. Frank SullowayDr. Frank Sulloway

In a recent study on birth order and intelligence, Norwegian researchers report that eldest children have higher I.Q.s than their younger siblings. Why would that be? There are as many guesses as there are scientists. “Virtually anyone who has a sibling is a birth-order theorist,” says Dr. Frank Sulloway, an expert on family dynamics at the University of California, Berkeley. Dr. Sulloway answered readers’ questions about the study and its implications; his answers appear below. [Editors’ note: questions are no longer being accepted.]