Mind & Body

Does Your Birth Order Really Matter?

We've all heard the conventional wisdom about birth order: oldest children are the responsible achievers, middle children the peacemakers, and youngest siblings the attention-seeking rebels. This "truth" is so often repeated that many people assume it's a scientific fact. But science has news for squabbling siblings and their long-suffering parents: Birth order means pretty much nothing at all.

So Rebellious

The idea that birth order affects adult personality has intuitive appeal. Most of us have observed new parents lavishing attention on their first born or watched younger siblings in big families clamoring for attention. But just because something meshes with everyday experience doesn't mean it has lasting effects that are supported by hard data.

Take the claim that youngest children grow up to be rowdy risk takers, for example. When a team of European researchers pored through data from three sources — a risk study of 1,500 Germans, a survey of 11,000 German households, and more than 100 famously risk-taking explorers and revolutionaries from history, they came to a simple conclusion: Being born last doesn't make you more likely to take risks.

"This paper is very clear and it convincingly shows that there are no birth order effects on risk-taking," was the blunt conclusion of one psychologist who gave his assessment of the study to The Washington Post.

This is not the first piece of research to poke holes in the conventional wisdom on birth order. Another massive 2015 study of 370,000 high school students in Houston found no correlation between the relative age of a person's siblings and their personality. A third study that same year looked at an international group of 20,000 participants and came to the same conclusion.

Taken together these results show the idea that birth order affects personality is a "'zombie theory' that lurches forward despite the evidence against it," concludes the same Washington Post article. Maybe it's time to let it die a dignified death.

A (Tiny) Light at the End of the Tunnel

Or maybe not, at least in one tiny area. While the evidence that birth order has no effect on personality is piling up, there are still concrete data showing oldest children have an advantage intellectually. But before you start sending snarky texts taunting your younger siblings, you need to understand exactly how small this effect is.

As psychologist Dieter Wolke explains on The Conversation, a careful recent examination of all the evidence on the matter showed "first-borns had, on average, an IQ of 1.5 points higher than second-born siblings, who in turn had a 1.5 higher IQ than third-borns and so on."

But lord this advantage over your younger siblings at your peril. One and a half IQ points is a truly tiny difference, and these findings are averages that mask a lot of diversity among families.

"Although this is a robust and statistically significant finding the IQ difference is small. It means that in six out of ten cases the older sibling will have a higher IQ than the next youngest sibling. Conversely, it also means that in four out of ten cases younger siblings have a higher IQ," cautions Wolke.

So maybe delete that message challenging your younger brother to dueling IQ tests after all. And forget about crowning yourself family diplomat or adventurer just because you were second or third born. Instead, the best of today's science suggests we should see our siblings as individuals, evaluating them based on who they are. Birth order isn't going to offer you any insights.

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Learn more about sibling relationships in "The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us" by Jeffrey Kluger. The audiobook is free with an Audible trial. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Jessica Stillman May 17, 2019

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