Birth order can affect human psychology, though many supposedly formative effects of birth order are instead related to other factors.
Birth order is defined as a person’s rank by age among his or her siblings. Birth order is often believed to have a profound and lasting effect on psychological development. This assertion has been repeatedly challenged by researchers, yet birth order continues to have a strong presence in pop psychology and popular culture.
Theories
Alfred Adler (1870-1937), an Austrian psychiatrist, and a contemporary of Sigmund Freud and Carl Jung, was one of the first theorists to suggest that birth order influences personality. He argued that birth order can leave an indelible impression on an individual’s style of life, which is one’s habitual way of dealing with the tasks of friendship, love, and work. According to Adler, firstborns are “dethroned” when a second child comes along, and this may have a lasting influence on them. Younger and only children may be pampered and spoiled, which can also affect their later personalities. Additional birth order factors that should be considered are the spacing in years between siblings, the total number of children, and the changing circumstances of the parents over time.
Since Adler’s time, the influence of birth order on the development of personality has become a controversial issue in psychology. Among the general public, it is widely believed that personality is strongly influenced by birth order, but many psychologists dispute this. One important modern theory of personality states that the Big Five personality traits of Openness, Conscientiousness, Extraversion, Agreeableness, and Neuroticism represent most of the important elements of personality that can be measured. Contemporary approaches to birth order frequently suggest that birth order influences these five traits.
In his book Born to Rebel, Frank Sulloway suggests that birth order has strong and consistent effects on the Big Five personality traits. He argues that firstborns are more conscientious, more socially dominant, less agreeable, and less open to new ideas compared to laterborns. However, critics such as Fred Townsend, Toni Falbo, and Judith Rich Harris, argue against Sulloway’s theories. An issue of Politics and the Life Sciences, dated September, 2000 but not published until 2004 due to legal threats from Sulloway (who claimed its content to be defamatory, although it was carefully and rigorously researched and sourced), contains criticisms of Sulloway’s theories, including studies that show conflicting findings.
In their book Sibling Relationships: Their Nature and Significance across the Lifespan, Michael E. Lamb and Brian Sutton-Smith make the point that sibling relationships often last an entire lifetime. They point out that the lifespan view proposes that development is continuous, with individuals continually adjusting to the competing demands of socialization agents and biological tendencies. Thus, even those concerned only with interactions among young siblings implicitly or explicitly acknowledge that all relationships change over time and that any effects of birth order may be eliminated, reinforced, or altered by later experiences.
Personality
Claims about birth order effects on personality have received only mixed support in scientific research. Such research is a challenge because of the difficulty of controlling all the variables that are statistically related to birth order. Family size, and a number of social and demographic variables are associated with birth order and serve as potential confounds. For example, large families are generally lower in socioeconomic status than small families. Hence third born children are not only third in birth order, but they are also more likely to come from larger, poorer families than firstborn children. If third-borns have a particular trait, it may be due to birth order, or it may be due to family size, or to any number of other variables. Consequently, there are a large number of published studies on birth order that vary widely in quality and are inconsistent in their conclusions.
Literature reviews that have examined many studies and attempted to control for confounding variables tend to find minimal effects for birth order. Ernst and Angst reviewed all of the research published between 1946 and 1980. They also did their own study on a representative sample of 6,315 young men from Switzerland. They found no substantial effects of birth order and concluded that birth order research was a “waste of time.” More recent research analyzed data from a national sample of 9,664 subjects on the Big Five personality traits of extraversion, neuroticism, agreeableness, conscientiousness, and openness to experience. Contrary to Sulloway’s predictions, they found no significant correlation between birth order and self-reported personality. There was, however, some tendency for people to perceive birth order effects when they were aware of the birth order of an individual.
Other studies have supported Sulloway’s claims about birth order. Paulhus and his colleagues found consistent support in self-reports by both student and adult samples. First borns scored higher on conservatism, conscientiousness and achievement orientation. Later borns scored higher on rebelliousness, openness, and agreeableness. The authors argued that the effect emerges most clearly from studies within families. Results are weak at best, when individuals from different families are compared. The reason is that genetic effects are stronger than birth order effects. Recent studies also support the claim that only children are not markedly different from their peers with siblings. Scientists have found that they share many characteristics with firstborn children including being conscientious as well as parent-oriented.
In her review of the research, Judith Rich Harris suggests that birth order effects may exist within the context of the family of origin, but that they are not enduring aspects of personality. When people are with their parents and siblings, firstborns behave differently than laterborns, even during adulthood. However, most people don’t spend their adult lives in their childhood home. Harris provides evidence that the patterns of behavior acquired in the childhood home don’t affect the way people behave outside the home, even during childhood. Harris concludes that birth order effects keep turning up because people keep looking for them, and keep analyzing and reanalyzing their data until they find them.
Jane Austen’s book Pride and Prejudice, while being a study on a certain form of courtship, also places stringent analysis on the personalities on five sequential daughters.