WORLD / Health
Firstborn sons have higher IQs: Study
(China Daily)
Updated: 2007-06-23 06:58
WASHINGTON: Firstborn sons have higher IQs than their younger brothers,
and their social status within the family might explain why, researchers
said on Thursday.
A study that used the military draft records of 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 an average
of 1.1 points.
Men who had been raised as the eldest, whether they were born first,
second, or third, had IQs to match their firstborn peers.
The same was true for those raised or born second, Petter Kristensen and
colleagues at the University of Oslo reported 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," Kristensen's team wrote in Science.
Their studies confirmed what many scientists had suspected for more than
a century - that firstborns have an edge.
But attempts to prove the effect have been disputed, in part because the
circumstances of each family are different.
To compensate for this, Kristensen's team studied brothers raised in the
same families.
And some scientists argue that birth order IQ differences arise in the
womb, while others point to family interactions.
To distill potential biological effects from social effects, Kristensen's
team dug up the young men's family birth records and found families whose
firstborn or first and second-born children had died before the age of
one year.
That was when they discovered that it was not birth order so much as
growing up as the eldest of the children in a family that made the
difference.
Agencies
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