All that stuff you’ve heard about first-born kids being this, middle kids being that … it’s probably all nonsense. (Except the part about third-borns being smart and humble.)
When people actually started studying siblings to separate fact from anecdote, they found that “where a child falls in the lineup makes no difference in terms of the Big 5 personality traits: extraversion, emotional stability, agreeableness, conscientiousness and imagination.”
But wait — there’s an exception. Twins. That’s the one time when birth order, even minutes apart, really can make a difference.
In an ironic twist, research suggests twins’ personalities may develop, in part, based on who is larger and healthier at birth. As it happens, the firstborn twin usually snags those defining characteristics.