Dekortage writes
"Eldest children have higher IQs than their siblings, according to a recent study by Norwegian researchers. The study focused on men, particularly 'on teasing out the biological effects of birth order from the effects of social status,' but indicates that the senior boy in a family (either by being firstborn, or if an elder brother died) has an average IQ two or three points higher than younger brothers. As noted in the New York Times coverage, 'Experts say it can be a tipping point for some people — the difference between a high B average and a low A, for instance... that could mean the difference between admission to an elite private college and a less exclusive public one.'"