Tests & Experiments
For other uses of the redirecting terms such as "little brother" and "big sister", see Brothers and Sisters.
"Last child" redirects here. For the song by Aerosmith, see Last Child.
Birth order is defined as a person's rank by the sequence of birth among his or her siblings. Birth order is commonly believed to have a profound and lasting effect on psychological development. Although this assertion has been repeatedly challenged by researchers, birth order continues to have a strong presence in pop psychology and popular culture.
TheoriesAlfred 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 [1] 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 researchMost of the claims about birth order have not been supported by scientific research. Indeed, many of the traits believed to be associated with different birth positions appear to contradict each other. Only children are supposedly more extraverted because they need to go outside of the family to meet other children, yet they are also believed to be more introverted so they can tolerate being by themselves. In fact, extraversion and introversion are stable personality traits, and they are related more strongly to genetic factors than to birth order. Firstborns are attributed with a variety of traits that do not even correlate with each other, much less with birth order. In general, birth order effects are weaker than commonly believed. In practice, systematic birth order research is a challenge because it is difficult to control for all of 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. This means that 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 thirdborns 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. It is often impossible to determine which variable is the actual cause of the observed trait. This methodological issue has plagued research in this area. Spacing of children, parenting style, and gender are additional variables to consider. Consequently, there is 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 (1983) 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 recently, Jefferson, Herbst, and McCrae (1998) 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. In her review of the scientific literature, Judith Rich Harris (1998) 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. Intelligence
Since the 1970s, one of the most influential theories to explain why firstborns frequently score higher on intelligence and achievement tests than other children is the confluence model of Robert Zajonc. This model states that because firstborns mainly have adult influences around them in their early years, they will spend their initial years of life interacting in a highly intellectual family environment. This effect may also be observed in siblings who, although later born, have a sibling at least five years senior with no siblings in between. These children are considered to be "functional firstborns". The theory further suggests that firstborns will be more intelligent than only children, because the latter will not benefit from the "tutor effect" (i.e. teaching younger siblings). Zajonc's theory has been criticised for confounding birth order with both age and family size, and alternative theories (such as Resource Depletion Theory) have been offered to explain the Belmont and Marolla findings. In a meta-analysis of the research, Polit and Falbo (1988) found that firstborns, only children, and children with one other sibling score higher on tests of verbal ability than laterborns and children with multiple siblings. This effect suggests that smaller families lead to children with higher test scores. Because there was no specific advantage for firstborn children, the results are consistent with Resource Depletion Theory, but not the confluence model. The basic finding that firstborns have higher IQ scores has been disputed. One group of researchers examined data from the National Longitudinal Survey of Youth (NLSY) (USA), which gave them the opportunity to look at a large randomly selected sample of US families. The sample included children whose academic performance had been reviewed multiple times throughout their academic careers. This study found no relationship between birth order and intelligence (Rodgers, Cleveland, Van den Oord, & Rowe, 2000). Recently, researchers reporting in the journal Science (June 2007) found that "the eldest children in families tend to develop slightly higher IQs than their younger siblings." [1] This could be a consequence of parents spending more quality time with their first-born children than with subsequent children [2]. SexualityThe fraternal birth order effect is the name given to the observation that the more older brothers a man has, the greater the probability is that he will have a homosexual sexual orientation. The fraternal birth order effect is the strongest known predictor of sexual orientation, each older brother increases a man's odds of being gay (Blanchard & Bogaerd, 1996). Even so, the fraternal birth order effect only accounts for a maximum of one seventh of the prevalence of homosexuality in men. There seems to be no effect on sexual orientation in women, and no effect of the number of older sisters. In the book, Homosexuality, Birth Order, and Evolution: Toward an Equilibrium Reproductive Economics of Homosexuality, Edward M. Miller suggests that the birth order effect on homosexuality may be a by-product of an evolved, biological mechanism that shifts personality toward the feminine direction in laterborn sons. This would have the consequence of reducing the probability of these sons engaging in unproductive competition with each other. Notes and references
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