The eldest children in families tend to develop slightly higher I.Q.s than their younger siblings, researchers are reporting, based on a large study that could effectively settle more than a half-century of scientific debate about the relationship between I.Q. and birth order.
The difference in I.Q. between siblings was a result of family dynamics, not biological factors like changes in gestation caused by repeated pregnancies, the study found....
The new findings, which is to appear in the journal Science on Friday, are based on detailed records from 241,310 Norwegians, including some 64,000 pairs of brothers, allowing the researchers to carefully compare scores within families, as well as between families. The study found that eldest children scored about three points higher on I.Q. tests than their closest sibling.
Three points on an I.Q. test, experts said, amount to a slight edge that could be meaningful for someone teetering between an A and a B, for instance, or even possibly between admission to an elite liberal-arts college and the state university, some experts said. They said the results are likely prompt more intensive study into the family dynamics behind such differences....
“I consider this study the most important publication to come out in this field in 70 years; it’s a dream come true,” said Frank J. Sulloway, a psychologist at the Institute of Personality and Social Research at the University of California in Berkeley.
Dr. Sulloway, who wrote an editorial accompanying the study, added, “There was some room for doubt about this effect before, but that room has now been eliminated.”...
Social scientists have proposed several theories to explain how birth order might affect I.Q. scores. First-borns have their parents’ undivided attention as infants, and even if that attention is later divided evenly with a sibling or more, it means that over time they will have more cumulative adult attention, in theory enriching their vocabulary and reasoning abilities.
But this argument does not explain a consistent finding in children under 12: among these youngsters, later-born siblings actually tend to outscore the eldest on I.Q. tests. Researchers theorize that this precociousness may reflect how new children alter the family’s overall intellectual resource pool. Adding a young child may, in a sense, dumb down the family’s overall intellectual environment, as far as an older sibling is concerned; yet the younger sibling benefits from the maturity of both the parents and the older brother or sister. This dynamic may quickly cancel and reverse the older child’s head start with mom and dad....
Another potential explanation concerns how individual siblings find a niche in the family. Some studies find that both the older and younger siblings tend to describe the first-born as more disciplined, responsible, a better student. Studies suggest — and parents know from experience — that to distinguish themselves, younger siblings often develop other skills, like social charm, a good curveball, mastery of the electric bass, acting skills.
Needless to say, I sent copies to my (younger) brother asnd sister. My sister, the "baby" of the family, responded that she is the most lovable. Quite so.
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