In spite of sharing genes and environments, siblings are often not as similar in nature as one might think. But where do the supposed differences come from? Alfred Adler, a late-19th- and early-20th-century Austrian psychotherapist and founder of individual psychology, suspected that birth order leads to differences in siblings.
Adler considered firstborns to be neurotic, because they don't have to share their parents for years and are essentially dethroned once a sibling comes along. He also considered oldest children dutiful and sometimes conservative. The youngest children are ambitious, while middle children are optimally positioned in the family and are characterized by emotional stability.
Every child occupies a certain niche within the family and then uses his or her own strategies to master life. Firstborn and single children had less reason to quarrel with the status quo and identify more strongly with the worldview of their fathers and mothers. Younger siblings are less sure of their parents' view and therefore more often choose alternative paths in life. Such categorizations are popular because they're rather intuitive, and one can always find an example of the sensible big sister or the rebellious young brother in their circle of acquaintances.
