LOS ANGELES, June 24 (Xinhua) — Eldest children are more likely to be more intelligent than their younger siblings, according to a new study.
Eldest children have IQs 2 to 3 points greater than younger siblings’, and the reason is not genetics, but the way their parents treat them, according to the study published in the latest issue of the journal Science.
Researchers at the University of Oslo collected data from 240,000 Norwegian men and found that firstborns had an average IQ of 103.2, about 2 points higher than second-born males and about 3 points higher than men born third.
Lead author Petter Kristensen, an epidemiologist at the University of Oslo and a second-oldest son, said he did not believe in the “birth-order effect” when he started his research, which was originally aimed at assessing the validity of IQ tests.
In the research, Kristensen and his colleagues required that all conscripts in the Norwegian army undergo an IQ test. Kristensen looked at test results of all conscripts ages 18 to 19 between 1985 and 2004.
His analysis found that firstborns had an average IQ of 103.2, about 2 points higher than second-born males and about 3 points higher than men born third.
Using the same data, the researchers sought to find an answer to the cause of this disparity. They looked at second- and third-born men who became the eldest in their families due to the death of one or two older siblings.
The researchers found that those men had IQs close to that of firstborns, with second-born men at 102.9 and third-borns at 102.6.
The findings suggested that the mechanism behind the birth-order effect is not biological but related to social interactions within families.
The researchers surmised that older children are showered with attention early in life and treated as leaders in the family. They are handed more responsibility after younger siblings are born and live with higher expectations from their parents.
Though the IQ disparity may not sound like a lot, experts said even a few IQ points could make a big difference over the course of a lifetime — and set firstborns on a trajectory for success.