Boys at the top of the pecking order  either by birth or because their older brothers died score higher on IQ tests than their younger brothers. Norwegian researchers now report that it's a matter of what they call social rank in the family that gives the first born the highest scores or, if the first born had died young, the next oldest. Kristensen and Bjerkedal studied the IQ test results of 241,310 Norwegian men drafted  into the armed forces between 1967 and 1976. All were aged 18 or 19 at the time. The average IQ of first-born men was 103.2, they found second-born men averaged 101.2, but second-born men whose older brother died young scored 102.9. And for third-borns, the average was 100.0. But if both older brothers died young,the third-born score rose to 102.6. The findings provide "evidence that the relation between birth order and IQ score is dependent on the social rank in the family and not birth order as such." they concluded.  _ since at least 1874,when Sir Francis Galton reported that men in noticeable positions tended to be firstborns more often than would have been statistically   expected. Since then, several studies have reported higher intelligence scores for firstborns, while other analyses have questioned those findings and the methods of those reports. "These two researchers prove that how study participants  were raised, not how they were born, is what actually influences their IQs," said Sulloway, an American professor, who was not part of the research team. "The elder child pulls ahead," he said, "perhaps as a result of learning gained through the process of tutoring younger brothers and sisters". "The older child benefits by having to organize and express its thoughts to tutor youngsters", he said, "while the later born children may have no one to tutor." According to Norwegain researchers' finding, which of the following is linked to boys' IQ?
Birth order Position in the family Parents' social rank Educational experience