Jun 25 2007
Scientists in Norway have confirmed after carrying out a large study that the order people are born in within a family may influence how smart they are.
The possibility of a connection between birth order and IQ levels is a factor which has been suspected for some time but until now the reasons were unclear.
According to a team at the University of Oslo, the eldest child is normally the one with the highest IQ and this they believe is the result of family up bringing rather than any biological difference.
In their study the researchers used data on birth order, status of earlier born siblings and whether they had died early in infancy, and IQ scores for nearly 250,000 male 18 and 19 year old Norwegian military conscripts who were drafted between 1985 and 2004.
They found on average around a 3 points higher IQ in the eldest brother when compared to the second son, and an average 1.1 point higher level in the second son when compared to the third.
Similar findings on the same subject, made in earlier studies were criticised on the basis that the families were all in different situations and the results were as a result subjective.
To avoid issues of biological effect and the differences complained about before Kristensen and his colleagues looked at brothers raised in the same families who had had lost their first born or first and/or second born children in the first year of their lives.
They say this demonstrated that it was how the boys were raised rather than the biological factor in birth order that made the difference.
The team also found that the differences in IQ were larger in brothers from smaller families and when the mothers were more highly educated but this factor disappeared as the age gaps between the brothers diminished.
Dr. Kristensen an epidemiologist at the National Institute of Occupational Health at the University, suggests as a rule the eldest child has greater expectations placed upon them and they take up the responsibility of looking after and watching out for their younger siblings and he says the same could apply to girls.
Dr. Kristensen is himself a second born and says these results went against his intuition because other studies show that first borns often suffer from poorer health.
He says parents should not be too concerned about the findings as having a high IQ and knowing how to use it are different attributes and though a child might score a few points lower in their IQ they well have other assets such as curiosity, imagination and what is called "emotional intelligence" that helps them use their IQ much more effectively.
The study is published in the journal Science.