Are you a rebellious youngest child, a responsible first-born, or perhaps a people-pleasing middle child? Much has been said about how birth order affects personality and intelligence. Is there any truth to the stereotypes?

Oldest, youngest or middle: does birth order affect personality? Image credit amyelizabethquinn via Pixabay

Neurotic, spoiled or independent?

Personalities are interesting things. We like to understand our own personalities and wonder how hard it might be to change our personality. We want to know if it’s possible to predict personality, for example on the basis of what time of year we were born. It’s also widely accepted that birth order influences personality.

It seems reasonable our position in the family – oldest, middle, youngest or only – might affect who we are. It’s not a new idea. Alfred Adler, a colleague of Sigmund Freud’s, suggested in the late 1920s that birth order affected personality.

Adler suggested firstborns feel ‘dethroned’ when a younger brother or sister comes along. The arrival of a new baby makes oldest children neurotic, but also good leaders. Adler proposed youngest children are likely to be spoiled, but also outgoing, whereas middle children are more independent. Only children revel in being the sole focus of their parents’ attention but as a result are more controlled and scrutinised.

Researchers have studied the influences of birth order for many years, but among thousands of studies, there hasn’t been a lot of consensus. In just the past two years articles have appeared with the headlines ‘Birth order is basically meaningless’ and ‘Research shows birth order really does matter’.

And of course in many families, the story is much less simple than these predictions suggest. Age gaps between children, the gender of each sibling, step-children and adoptions may all have an effect. And in a big family, there are many middle children. So is there any evidence for Adler’s theories?

First-born advantage

If you’re the eldest in your family, you may have already taken note of the many claims you’re likely to be smarter and more successful than your younger siblings. Perhaps you’ve heard you’re more likely to become a president, or an astronaut, or to make more money. Potentially dubious online reporting aside, there is some truth to the idea of the first-born advantage.

Francis Galton noticed many scientists in the 19^th century were first-borns. First-borns are more likely to be managers or take on other occupations that require leadership. In a 2015 study of more than 20,000 people from the US, UK and Germany, researchers did find first-born children score higher on IQ tests. The theory goes that parents have more time and energy to give their first child and this boosts that child’s intelligence. Kids who come later have to share their parents’ attention.

A study of 5000 American children found beginning at a young age, first-born kids do better on a variety of tests including reading, comprehension and maths. The researchers found younger siblings weren’t born at a disadvantage, but they got less mental stimulation from their parents as their parents became busier with a larger family. Other studies have suggested the same effect.

A large study of families in Denmark and the US found that in families with two or more children, second-born sons were much more likely to be disciplined at school and end up in trouble with the police than their older brothers. And a study carried out in Chile showed first-borns are less likely to use drugs.

Finding your place

The idea that birth order shapes personality comes from the evolutionary view that siblings compete with each other to get their parents’ attention. The best way to do this is to be different to your brothers and sisters – to stand out. For example, younger siblings need more help than their big brothers and sisters so they become outgoing and extraverted to get attention.

Interestingly, our birth order does influence who we are more likely to form close relationships with. First-borns are more likely to be married to, or friends with other first-borns, middle children with other middle children and the baby of the family is also more likely to be in a relationship or close friendship with other youngest siblings.

A study of 377,000 U.S. high school students found only a small effect of birth order on personality. Oldest children did tend to be a little more conscientious and dominant, and less sociable (although more agreeable). But these results were only significant because the researchers studied so many thousands of people. And the large study of US, UK and German families found no effect of birth order on any of the ‘Big Five’ personality traits: openness, conscientiousness, extraversion, agreeableness and neuroticism. So we certainly don’t have good evidence for the personality stereotypes we so often hear about.

Regardless of birth order, there’s no question the relationships we have with our brothers and sisters have a strong influence on us. And I count myself very lucky to have two wonderful big brothers.

But now I’d better get off the computer and go back to trying to be the centre of attention, just in case.

Links and stuff

• Why first-born children are better leaders: The Atlantic
• How parents shape the advantages of being first born: The Conversation
• The hidden power of siblings: Jeff Kluger Tedx talk
• First-borns may have higher IQ but sibling bonds are what really shape our future: The Conversation