First Born, Middle, Last Born, Only, Twins

First-Borns
More conscientious, ambitious and aggressive than their younger siblings, first-borns are over-represented at Harvard and Yale as well as disciplines requiring higher education such as medicine, engineering or law. Every astronaut to go into space has been either the oldest child in his or her family or the eldest boy. And throughout history -- even when large families were the norm -- more than half of all Nobel Prize winners and U.S. presidents have been first-born.
Famous eldest children include: Hillary Clinton, Bill Clinton, Richard Branson, J.K. Rowling and Winston Churchill. And macho movie stars are First-Born, too, including Clint Eastwood, John Wayne, Sylvester Stallone, Bruce Willis and all the actors who have played James Bond.


Middles
Middle children are more easy going and peer-oriented. Since they can get lost in the shuffle of their own families, they learn to build bridges to other sources of support and therefore tend to have excellent people skills. Middle children often take on the role of mediator and peacemaker.
Famous middle children include: Bill Gates, J.F.K., Madonna and Princess Diana.


Youngest
The youngest child tends to be the most creative and can be very charming -- even manipulative. Because they often identify with the underdog, they tend to champion egalitarian causes. (Youngest siblings were the earliest backers of the Protestant Reformation and the Enlightenment.)
Successful in journalism, advertising, sales and the arts.
Famous youngest children include: Cameron Diaz, Jim Carrey, Drew Carey, Rosie O'Donnell, Eddie Murphy and Billy Crystal.


Only Children
Only children have similar characteristics to first-borns and are frequently burdened with high parental expectations. Research shows they are more confident, articulate and likely to use their imagination than other children. They also expect a lot from others, hate criticism, can be inflexible and are likely to be perfectionists.
Famous only children include: Rudy Guiliani, Franklin Delano Roosevelt, Alan Greenspan, Tiger Woods, tennis' teen queen Maria Sharapova and Leonardo Da Vinci.


Twins
Because they hold equal status and are treated so similarly, twins turn out similarly in most cases.
Famous twins include: advice columnists "Dear Abby" and "Ann Landers" (Abigail and Esther Friedman), and Harold and Bernard Shapiro, who became presidents of Princeton University and Canada's McGill University respectively.

Dr. Frank Sulloway, a behavioral scientist and visiting professor at the Institute of Personality and Social Research at University of California, Berkeley and author of the book, 'Born To Rebel: Birth Order, Family Dynamics and Creative Lives,' says first-borns are more similar in personality to first-borns in other families than they are to their own younger siblings. He adds that youngest children are often more similar to the youngest child in another family than his or her own elder siblings. He says this is because the family is not as much a "shared environment" as a set of niches that provide siblings with different outlooks.
Conley agrees, but stresses that these are just general trends -- and that the whole birth-order theory can be turned on its head depending on the child's personality, the age gap between siblings and the family circumstances each child experiences during his or her formative years.