Sibling rivalry

A new study in Science reports that the eldest children in families tend to have slightly higher IQs than their younger siblings. The report (brought to my attention by, not surprisingly, my older sister) concluded that the small but significant difference (2.3 IQ points) was not a result of biology, but rather social upbringing.

From The New York Times:

Norwegian epidemiologists analyzed data on birth order, health status and I.Q. scores of 241,310 18- and 19-year-old men born from 1967 to 1976, using military records. After correcting for factors known to affect scores, including parents’ education level, birth weight and family size, the researchers found that eldest children scored an average of 103.2, about 3 percent higher than second children and 4 percent higher than the third-born children. The scientists then looked at I.Q. scores in 63,951 pairs of brothers and found the same results. Differences in household environments did not explain elder siblings’ higher scores.

To test whether the difference could be caused by biological factors, the researchers examined the scores of young men who had become the eldest in the household after an older sibling had died. Their scores came out the same, on average, as those of biological first-borns.

Blame your parents:

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.
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Older siblings [also] consolidate and organize their knowledge in their natural roles as tutors to junior. These lessons, in short, could benefit the teacher more than the student.

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.

I have failed to develop any such skills (although my Wii-curveball is improving), but all is not lost, little ones! There is a glistening, titillating silver lining to this cloud of inferiority:

Younger siblings often live more adventurous lives than eldest siblings. They are more likely to participate in dangerous sports than eldest children and more likely to travel to exotic places, studies find. They tend to be less conventional in general than first-borns, and some of the most provocative and influential figures in science spent their childhoods in the shadow of an older brother or sister (or two or three or four).

Charles Darwin, author of the revolutionary “Origin of Species,” was the fifth of six children. Nicolaus Copernicus, the Polish astronomer who determined that the Sun, not the Earth, was the center of the planetary system, grew up the youngest of four. René Descartes, the youngest of three, was a key figure in the scientific revolution of the 16th century.

First-borns have won more Nobel Prizes in science than younger siblings, but often by advancing current understanding, rather than overturning it, Dr. Sulloway argued. “It’s the difference between every-year or every-decade creativity and every-century creativity,” he said, “between creativity and radical innovation.”

Link to the NYT article.