There's good reason behind the eldest child superiority complex then?

If you are the eldest child in your family, you've probably known this for a long time. If you are not the eldest sibling, you've probably known for a long time that the eldest child thinks this.

But it turns out there's some cold, hard scientific evidence behind the eldest sibling superiority complex (or what some might just call plain arrogance).

A study published in the Proceedings of the National Academy of Sciences (PNAS) journal examined the long-standing question of whether a person's position among siblings has a lasting impact on their life course.

For decades, researchers have tried to establish whether someone's position in their sibling birth order has a lasting impact on their intelligence and personality.

And it turns out that when it comes to intelligence, it does.

The study found there was an observed effect of around 1.5 IQ points for each increase in birth-order position.

For people with one or two younger siblings, there was a marked difference in their IQ to that of the second-born child.

Meanwhile, for four-sibling families, the IQs of the first and second-born children were very similar, before a noticeable drop-off for the third and fourth-born children.

However, the birth order of siblings has seemingly no effect on personality traits such as extraversion, emotional stability, agreeableness, conscientiousness, or imagination.

This isn't the first time a study has found that first born children tend to have a higher IQ than their siblings.

Back in 2017, research from the University of Edinburgh concluded that eldest children demonstrated higher IQs from the age of one onwards.

The study, which involved 5,000 children who were monitored from their birth until they were 14-year-old, concluded this was down to the fact first born children usually received the complete attention of their parents in their formative years.