Numerous studies suggest that we’re likely to share some of the same personality traits with people in other families who share the same birth order. For example, because firstborns are older, they’re the first to receive privileges and the first to be asked to take care of younger siblings. The firstborns’ position makes them feel special and, at times, burdens them – and their personalities are likely to reflect a mixed bag. For example, they’re likely to be leaders, but they may also be hard to get along with and are most likely to feel insecure and jealous. Middle children tend to be diplomats, while last-borns are the rebels-with or without a cause. Having been picked on and dominated by the firstborns, later children are more likely to be open to new ideas and experiences and support innovative ideas in science and politics. Later-born children are also more agreeable and more sociable- firstborns may be most likely to achieve, but later-borns are clearly more popular. Do you think all the birth order stuff is nonsense? Mention it to the next Ph.D you meet. About 90 percent of people with doctorates – not to mention the vast majority of U.S. presidents – are first-borns or only children! Astronauts are also disproportionately firstborns.
Source: Johnston, J. (2009) The Complete Idiot’s Guide to Psychology, Penguin Group: New York