A long-held stereotype is that 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 Time (October 29, 2007). The studies bring rigor to the notion that birth order affects fundamental personality traits.
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 childs' roles as mentors. These advantages might explain why eldest children are overrepresented among board directors, MBAs and surgeons.
Within families, the youngest children tend to have to struggle for attention--and in doing so resort to subversive behavior. While birth order's effects are clearest for the youngest and elder children, the effect on middle children remains murky.