If you're the eldest of several siblings, you could have a small IQ point advantage.
Credit: iStockphoto
PERTH: Being the eldest sibling in a family may boost your IQ, according to a new study, which adds to evidence that social rank affects intelligence.
The research suggests that children raised as the eldest in the family – irrespective of actual birth order – had higher IQ scores than those who were second or lower in position in their family.
"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," said authors Petter Kristensen, from the National Institute of Occupational Health and Tor Bjerkedal, from the Institute of Epidemiology, both in Oslo, Norway.
Sibling rivalry
To gather data, the pair studied almost a quarter of a million Norwegian armed services conscripts aged 18 and 19, looking at figures on birth order, family situation and IQ status.
They found that the eldest child in the family had an average IQ of 2.3 points higher than their younger siblings – even if they had elder siblings who had passed away. For example, second born children who were raised as the eldest after a sibling died, had IQ scores comparable to other first borns, and higher than second borns in other families.
The findings are detailed today in the U.S. journal Science.
The link between intelligence and birth order has been controversial since it was first suggested, as far back as 1874. In recent years several theories have been proposed for the difference, including social interactions in the family, or biological factors in the womb. Some experts have even questioned whether the trend is real or down to errors in the data.
According to Kristensen, the social interaction hypothesis takes into account factors such as how attention and resources are shared within a family.
"The parents have a limited amount of resources and time for their children, this may favour the elder because they have some time when there are fewer children to share those resources," Kristensen told Cosmos Online.
Several point advantage
He said that while their data is not comprehensive enough to give direct support to the social interaction theory, "the results give fairly clear evidence against other [the other] explanations."
The 2.3 point IQ difference is actually fairly significant, commented psychologist Frank Sulloway of the University of California in Berkeley, in an accompanying commentary also published in Science
"[That kind of difference] can have far greater consequences than most people imagine," he said. "In medicine, new therapeutic benefits of this magnitude often make front-page headlines."
Kristensen says that while the IQ difference may be quite significant on a population level, at the individual level it is unlikely to cause much of a difference.
