How Being an Older (or Younger) Sibling Affects Personality

Under a long-held stereotype, first-born children tend to be highly competent, while their younger siblings are more likely to wind up the family laggards. Increasingly, scientific studies are finding that there is truth behind the typecasting, reports Jeffrey Kluger in the.

The studies bring rigor to the notion that birth order affects fundamental personality traits. It’s an idea that many people take for granted, Mr. Kluger observes, noting that few people are surprised by the troubled lives led by Billy Carter, Roger Clinton and the alcoholic Elliott Roosevelt compared with their presidential elder brothers Jimmy, Bill and Theodore.

Birth order seems to influence behavior in several ways. Families bestow greater resources and attention on the first-born, and eldest children often adopt the role of caretaker toward younger siblings. A Philippine study found that later-born siblings weigh less than earlier-borns. According to a Norwegian study, the eldest child enjoys on average a three-point IQ advantage over the next eldest sibling, a gap attributed to the older kids’ roles as mentors to the younger children. These advantages might explain why eldest children are overrepresented among board directors, M.B.A.s and surgeons.

Within families, the youngest children tend to have to struggle for attention — and in doing so resort to subversive behavior. This isn’t always to their disadvantage. Some of the most famous satirists have been later-borns — Jonathan Swift, Mark Twain and Stephen Colbert.

Frank Sulloway, a visiting scholar at the University of California, Berkeley, who has studied the impact of birth order, says that later-borns also are more willing to take on risk. For instance, research by Ben Dattner, a professor of organizational psychology at New York University, shows that firstborn chief executives prefer to make incremental improvements, while later-born CEOs are more likely to make transformational changes.

While birth order’s effects are clearest for the youngest and elder children, the effect on middle children remains murky. And the larger a family is, the less of an impact birth order seems to have. –