Elder siblings are likely to be more intelligent than their younger brothers and sisters, a major new study has found.
The findings, published in the Proceedings of the National Academy of Sciences journal, suggest first-borns develop quicker because they can ‘tutor’ younger siblings as they explain how the world works.
The study also contradicts widely held beliefs that first-borns are often perfectionists and last-borns rebellious.
Through analysing data from more than 20,000 adults across Germany, the US and Britain, psychologists from the University of Mainz and Leipzig University also found that personality traits such as extraversion, emotional stability, agreeableness, conscientiousness and imagination were not affected by birth-order position.
Professor Stefan Schmukle, from Leipzig University, said they “found no substantial effects of birth order on any of the personality dimensions we examined”.
“This does not only contradict prominent psychological theories, but also goes against the intuition of many people,” he added.
After first-borns reported in the study they were more likely to have a richer vocabulary, researchers confirmed a small decline in intelligence for younger siblings.
“This effect on intelligence replicates very well in large samples, but it is barely meaningful on the individual level, because it is extremely small,” said Professor Schmukle.
“And even though mean scores on intelligence decline, in four out of 10 cases, the later-born is still smarter than his or her older sibling," he said.
Julia Rohrer of Leipzig University said first-borns may be more intelligent because they taught their younger siblings about the world, according to Health Day.
“A first-born can ‘tutor’ their younger siblings, explaining how the world works and so on. 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 – which could be a boost to intelligence for some firstborns," she said.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies