Discussions

Birth order can have a significant impact on our personalities, relationships, choices, and the lives we ultimately lead. This influence is thought to be due to differential treatment a child receives depending on how he or she fits into the family structure (in addition to the nature of the home environment itself). Even when siblings live in the same household, the experiences they have growing up due to birth order can have a huge impact.  
 
Although the influence of birth order on personality is complex, there are exceptions to the amount of influence it can have. Factors such as family size, presence of step-children and half-siblings, adoptions, divorce, remarriages and deaths in the family are only a few of the elements that complicate the influence of birth order on personality. Also, the way that you are raised, including how your parents treat you and the type of environment in which you grow up (harmonious, chaotic, unpredictable, etc.) will all have a dramatic effect on your personality as well.  
 
In addition, the same personality characteristics may play out differently depending on a person's situation and background. For example, eldest children tend to be high achievers. This personality characteristic may be demonstrated in a variety of ways. In some eldest children, achievement is demonstrated through obtaining advanced degrees, high salaries and entering prestigious professions. Other eldest children may naturally gravitate toward leadership roles in adulthood, as the experience of being in control and calling the shots is something that becomes familiar to them.  
 
Finally, even though there are numerous family types, psychologists typically study nuclear families with one to three biological children. Other family units are usually not considered and the influence of birth order on personality in "non-traditional" families is not so well understood.  
 
Still, birth order, though not perfect, is a way to help you understand yourself better. You can use your birth order to get additional insight into what motivates you and why.  
 
For more reading:  
Adler, A. (1964). Social interest: A Challenge to Mankind. New York: Capricorn Books.  
 
Belmon, L. & Marolla, F.A. (1973). Birth Order, Family Size, and Intelligence. Science, 182, 1069-1101.  
 
Breland, H. (1974). Birth Order, Family Constellation, and Verbal Achievement. Child Development, 45, 1011-1019.  
 
Falbo, T. (1981). Relationships Between Birth Category, Achievement, and Interpersonal Orientation. Journal of Personality and Social Psychology, 41, 121-131  
 
Sulloway, Frank. Born to Rebel: Birth Order, Family Dynamics, and Creative Lives. (New York: Pantheon.) 1996.  
 
Zajonc, R.B., Markus, H. & Markus, G.B. (1979). The Birth Order Puzzle. Journal of Personality and Social Psychology, 37, 1325-1341.