Birth order may not shape personality after all

Birth order, according to conventional wisdom, molds personality: Firstborn children, secure with their place in the family and expected to be the mature ones, grow up to be intellectual, responsible and conformist. Younger siblings work harder to get their parents’ attention, take more risks and become creative rebels.

That’s the central idea in psychologist Frank J. Sulloway’s “Born to Rebel,” an influential book on birth order that burst, like a water balloon lobbed by an attention-seeking third-born, onto the pop psychology scene two decades ago. Sulloway’s account of the nuclear family claimed that firstborn children command their parents’ attention and resources, so later-borns must struggle to carve out their niche. Sibling behaviors then crystallize into adult personalities.

“I thought — and I still think — it’s very plausible and intuitive,” said Ralph Hertwig, a psychologist at the Max Planck Institute for Human Development in Berlin, who published a study on unequal parental investment with Sulloway in 2002.

The trouble is the growing pile of evidence, Hertwig’s included, that’s tilted against it.

Birth order does not appear to influence personality in adults, according to several ambitious studies published in the past few years. This new wave of research relied on larger data sets and more robust statistical methods than earlier reports that claimed to find a relationship between birth order and personality. Hertwig, for his part, predicted he would find evidence that later-borns are daredevils when he embarked on a recent study of risky behaviors. He did not.

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