Stereotype: Natural leader, ambitious, responsible.
Why it's true: The eldest, for a while, has no competition for time (or books or baby banter) with Mom and Dad. "There's a benefit to all of that undiluted attention. A 2007 study in Norway showed that firstborns had two to three more IQ points than the next child," says Frank J. Sulloway, Ph.D., the author of Born to Rebel. Firstborns tend to be surrogate parents when other siblings arrive, hence their protective and responsible nature.
When it's not: Parents can set high expectations for a first (or only) child. "When he feels like he has disappointed his parents or can't measure up, he may veer off in another direction," says Kevin Leman, Ph.D., a psychologist and the author of The Birth Order Book.
The middle child
Stereotype: Social butterfly, peacekeeper, fairness-obsessed.
Why it's true: "Middle-borns don't have the rights of the oldest or the privileges of the youngest," says Catherine Salmon, Ph.D., a coauthor of The Secret Power of Middle Children. As a result, they become experts at negotiation and compromise. They also tend to lean on their friends, as their parents' attention is often focused on the oldest or youngest child.
When it's not: If the oldest doesn't act the part, "it creates a job vacancy," says Salmon. "Donald Trump is a middle with a firstborn brother who didn't fit the role. Donald usurped it." And what if there are several middle children? "There's a principle that each child is trying to be different from the one immediately older," says Salmon. "So if you had three middles, the first and third would likely be a bit more similar to each other than to the very middle child."
Stereotype: Free spirit, risk taker, charming.
Why it's true: Parents are less cautious. (Hey, the older ones ate the dog's food and lived!) And they also probably have more resources than they did when starting out. "Parents are more lenient, so youngest kids tend to be less rules-oriented, and yet they still get lots of attention," says Salmon.
When it's not: "Some babies resent not being taken seriously," says Linda Campbell, a professor of counseling and human development at the University of Georgia, in Athens. "They might become very responsible, like the oldest, or social, like the middle."
5 things that throw it all off
Don't feel like your birth order? You're not alone. According to the White-Campbell Psychological Birth Order Inventory (or PBOI)—a test developed to measure whether people are a "fit" for their rank—only 23 percent of women and 15 percent of men are a true match. Here's why.
Nothing affects personality development more than genetics. Roughly half of your personality is the temperament you're born with, says Sulloway. And that's why where you fall in your family or how early you had to start sharing blocks is only part of the pie. A child's temperament can trump birth order—or at least blur the lines. Firstborns, in particular, are expected to succeed at whatever the family prizes most. (Son, you come from a long line of politicians...) So when they