"The researchers say the difference is due to social, not biological, factors, as younger siblings have higher IQs if they are raised as an eldest child following the death of an older brother or sister. The findings could suggest better ways of parenting the youngest children in a family."

"Petter Kristensen, at the University of Oslo in Norway, and colleagues reviewed data collected from 18- and 19-year-old men drafted into the country's military between 1985 and 2004. These young men took intelligence tests as part of their compulsory military service."

"Researchers then looked at the Norwegian birth registry to determine whether these men had older or younger siblings. Medical records also indicated whether their siblings had died shortly after birth, or at a relatively early age."

"The analysis revealed that firstborn men have, on average, an IQ that is about 2.3 points higher than those who are second-born. The trend continues such that second born men have higher IQs than their third-born brothers, and so on."

"In the US, SAT exams in reading and mathematics have a combined total of 1600 points, and on these two sections a difference in IQ of 2.3 could mean a 30 point difference in scores, says Frank Sulloway, at the University of California, Berkeley, US. This can mean the difference between getting into a premier university or second-tier university in the US, he points out."

"A further review of about 600 families that included at least four children showed that the eldest sibling typically has an IQ that is 2.9 points higher than the fourth-born sibling ("

"Sulloway calculates that a 2.3 IQ score difference means that the eldest child has a 13% higher chance of having above-average intelligence than
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