Firstborns are brainier. Firstborns are disproportionately represented in the Ivy League, with one study showing that 66 percent of incoming students were the eldest sibling in the family. Twenty-one of the first 23 U.S. astronauts were firstborns or only children. Firstborns dominate law firms and investment banks. Last-borns tend to be less educated, more likely to become comedians or artists. "The thinking behind this is that older siblings benefit from more alone time with parents. When a younger child comes along, the older one benefits from mentoring the younger one," says Kluger, noting that one study found that firstborns have a three-point IQ advantage over the next eldest.
Girls fight dirtier. In the childhood war for parental love and attention, Kluger says, sister-on-sister fighting has a distinct edge. "Boys tend to use high-powered strategies: I can punch you harder, and therefore I win," he says. "Girls often bring a much subtler, more psychological element. They tend to have a sense of the emotional weak spots of their opponent — and how to exploit them."
Singletons catch a break. Decades ago, the prevailing thinking was that being an only child was a "disease," Kluger says. "Now we know that singletons tend to work faster and have better vocabularies; they develop a confidence and self-contained quality." He cites an overscheduled lifestyle. "Kids get socialization in school and then at after-school activities," he says. "Then they're up at 7 a.m. for swim practice."
Parental favoritism hurts ... the favored child. Pampered kids can face a rude shock in the real world — where they're not always so special.
