Older siblings are considered more likely to be reliable, independent, and high achievers. Middle children are said to be somewhere rebellious, people-pleasing, and with large social circles, while youngest children are thought to be carefree, attention-seeking, and self-centered. Birth order stereotypes abound, but is there truth to them?

A study published Monday in the Proceedings of the National Academy of Sciences by German researchers appear to think so, concluding that the first-born tends to be smarter than younger siblings.

The team found that consistent with several earlier studies, oldest children scored higher on intelligence tests, with IQ and the person’s perception of his or her intelligence decreasing as the sibling rank goes down.

The team analyzed about 5,200 Americans, 4,500 British people, and 10,500 Germans to compare individuals within families and versus other sibling sets. The IQ and personality tests included questions on one’s birth order and IQ, self-reported intelligence, and big-five personality traits: agreeableness, consciousness, emotional stability, extroversion and imagination.

They evaluated significant and close age gaps and obtained similar results.

“It was surprising the results are so clear,” said Julia Rohrer, a study author and University of Leipzig psychology graduate student.

After IQ, birth order and character did not exhibit a strong connection between each other.

What could then be one reason for higher IQs among firstborns? Rohrer said it might be due to first-time parenting, therefore being prone to closely attending to the needs of the only child and stressing on the value of education.

It could also be a self-fulfilling prophecy: a specific kid reflects a birth order stereotype, so the other siblings tend to follow suit.

Another possible factor in the results, added the researchers, is the tutoring hypothesis, where a first-born can “tutor” younger siblings and explain the ways of the world.

Rohrer explained that teaching others requires “high cognitive demands,” with the children needing to draw from their own knowledge bank, structuring the information, and devising a way to explain it to the younger ones. This could boost the first-born’s own intelligence.

According to University of California Berkeley Professor Frank Sulloway, the researchers used very broad categories, possibly missing birth order effects. He said that the birth order effects on personality may also be “canceling themselves out at the collective trait level” — firstborns are deemed assertive (extroversion trait) while last-borns are expected to be sociable yet less talkative.

Sulloway argued that the two extroversion aspect traits, namely high assertiveness and low sociability, cancel each other out.

Photo: David Goehring | Flickr

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