Firstborn sons have higher IQs than their younger brothers, and their social status within the family may explain why, researchers reported on Thursday.
A study that used military draft records for more than 240,000 Norwegian men found that firstborns had an edge of 2.3 IQ points on their next oldest brothers, who in turn beat brothers born third by 1.1 points on average.
Men who had been raised as the eldest, whether they were born first, second, or third, had IQs to match their first-born peers. The same was true for those raised or born second, Petter Kristensen and colleagues at the University of Oslo report in the journals Science and Intelligence.
“This study provides 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,” Mr. Kristensen’s team wrote in Science.
Their studies confirmed what many scientists had suspected for more than a century — that firstborns have an edge.
I believe that your first born does so well because you have more time to spend with them. After additional children arrive you have to split your time amongst everyone which reduces the quality time they all get.