Now, now, children, there’s to be no more squabbling over who’s the smartest, because a new study has settled that question.

Oldest siblings tend to have the highest IQ, according to research by the University of Leipzig that looked at three studies involving 20,000 people. And there's more bad news for the non-firstborn: Each successive sibling in the family has a lower IQ score than the last.

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Don’t blame genetics just yet — the scientists say how kids are raised is the more likely cause. Researchers believe that younger siblings are generally given more freedom to do what they want, while firstborn kids are under more pressure to achieve. 

"One theory is that following children ‘dilute’ the resources of their parents,” says study co-author Julie Rohrer. "While the firstborn gets full parental attention, at least for some months or years, late-borns will have to share from the beginning.”

The fact that they usually pass on their knowledge to their siblings could also explain the increase in IQ. "Teaching other people has high cognitive demands — the children need to recall their own knowledge, structure it and think of a good way to explain it to younger siblings, which could provide a boost to intelligence for some firstborns,” the researcher adds.

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The scientists, after analyzing the results of IQ and personality tests, noticed a clear drop in intelligence, while a similar effect was noted on self-reported intellect.

However, contrary to popular belief, they found no birth order effects on extraversion, emotional stability, agreeableness, conscientiousness or imagination, which they theorize means that the development of personality isn’t necessarily determined by a sibling’s role within the family.