Does Birth Order Determine Personality?

May 21, 2004 — -- Some people say you are the kind of person you are because of when you were born in your family. They say, for example, being born first makes you more responsible.

That seems to hold true in the Cowan home, a North Carolina family who agreed to let 20/20 videotape some of their family interactions. Their first-born child, Jonathan, is very serious. His younger sister, Ellen, likes to torture their youngest brother, Jameson.

Jonathan often intervenes. In one instance, we saw him dragging his sister to the kitchen, telling his mother to discipline her. Jonathan agrees he's responsible. He says it's his job to help parent his younger siblings. "You have to watch over them when the parents are gone," he said.

That pattern fits what I've heard a lot about. A number of researchers say, where you fit in your family has a big influence on how you will act, how well you do in school and how much money you'll make. They say first-borns earn the most.

Some researchers say birth order differences are as strong as gender difference. "Within the family, they are about as strong as gender differences," according to Frank Sulloway, author of "Born to Rebel". In his book, Sulloway says later-borns tend to rebel because they often can't do what their older siblings can do, so they start trying to find other ways, even dangerous ones, to get their parents' attention.

"Younger siblings are more inclined to try these experimental, sometimes dangerous things," Sulloway said.

Sulloway points out that leaders of revolutions — like Thomas Jefferson, Karl Marx and Fidel Castro — were rebellious younger brothers. He says older brothers are often more conservative — like former Presidents Carter and Clinton and their younger brothers, Billy and Roger. Billy Carter had a beer-making business, and Roger Clinton tried a singing career — far cries from presidential politics.

Sulloway said younger siblings "tend to pick interests that are diametrically opposite to those of their older siblings. They're the risk takers, the adventurers, the people who are constantly trying to find something new and different to do."

Sulloway's got my number. I've taken all kinds of risks, including stupid ones, pursuing my career as a reporter, while my older brother, Tom, lives a much more conservative life, working as a research scientist. He even wears a bow tie, like our father did.

Sulloway also says later-borns rebel by choosing different professions.

He's got me again. I wanted to be a doctor, but became a reporter only because Tom was already a successful doctor, and I didn't think I could compete.

Later-borns rebel, says Sulloway, because they're controlled by the first-born. "Typical first-born strategy is to use the advantages of age, size and power to dominate a younger sibling," Sulloway says.

He pegged us again. When I was born, my brother says one of his first thoughts was that he had somebody to beat up. Tom said, "My best friend beat me up all the time. So it was nice having someone I could turn around and beat up."

But Dalton Conley, author of "The Pecking Order," another book on the effects of birth order, says, "birth order makes about as much sense as astrology, which is almost none."