In This Article Expand or collapse the "in this article" section Birth Order

  • Introduction
  • General Overviews
  • Journals
  • Parental Investment
  • Sibling Niche Theory
  • Methodological Issues and Research Design
  • Politics and the Life Sciences Controversy: Agendas and Methodology
  • Birth Order Stereotypes
  • Personality
  • Family Dynamics
  • Friendship and Cooperation
  • Sexual/Romantic Relationships
  • Sexual Orientation and the Fraternal Birth Order Effect
  • Education
  • Intelligence
  • Challenges to Confluence Theory of Intelligence
  • Theory of Mind/Cognitive Skills
  • The Workplace
  • Religion and Politics
  • Risk-Taking
  • Consumer Behavior
  • Mental and Physical Health

Psychology Birth Order
Catherine Salmon
  • LAST REVIEWED: 28 May 2019
  • LAST MODIFIED: 29 October 2013
  • DOI: 10.1093/obo/9780199828340-0103


Birth order, defined as an individual’s rank by age among siblings, has long been of interest to psychologists as well as lay-people. Much of the fascination has focused on the possible role of birth order in shaping personality and behavior. Many decades ago, Alfred Adler, a contemporary of Sigmund Freud and Carl Jung, suggested that personality traits are related to a person’s ordinal position within the family. He claimed that firstborns, once the sole focus of parental attention and resources, would be resentful when attention shifted upon the birth of the next child, and that this would result in neuroticism and possible substance abuse. In his view, lastborns would be spoiled and emotionally immature, while middle children would be the most stable, as they never experienced dethronement or being spoiled. Adler’s work led to an explosion of birth order studies examining the relationships between birth order and pretty much any topic one can think of, from personality traits to psychiatric disorders, intelligence, creativity, and sexual orientation. Not all of the research employed controls for other relevant factors, a number of hard-hitting critiques of the field were made, and the number of studies being done waned. Currently, the common view is that genetic differences account for a substantial portion (around 40 percent) of the variance in personality, for example, but that a similar amount of variance (around 35 percent) is due to non-shared environment, while the remainder is due to shared environment and measurement error. Birth order is one part of the non-shared environment. Siblings may grow up in the same family, but they do not all experience that family environment in the same way. Recently, researchers have suggested that birth order shapes strategies for dealing with the family environment, some of which may manifest themselves in settings outside the family domain. The first section of this article introduces general overviews or reviews of the birth order literature as well as some general theoretical perspectives and aspects of the debate over the important of birth order effects. The remaining sections examine the research in various areas where birth order has been well studied.

General Overviews

A wide variety of articles and books provide insight into the theoretical perspectives on birth order as well as reviewing portions of the field. Birth order research touches on many somewhat specialized areas of psychology; for example, cognition, child and lifespan development, social, and personality psychology, and reviews typically focus on just one specific aspect, most frequently personality. Research can be largely atheoretical or may come from an Adlerian perspective or a Darwinian one. There are a number of books and reviews that challenge the impact of birth order, including Harris 1998, and just as many that argue for strong effects, such as Sulloway 1996 and Sulloway 2010. Those interested in mastering the birth order literature have a lot of reading ahead of them; thousands of articles have been published. But the articles and books included here will acquaint the reader with the major debates within the field and will highlight the most consistent of findings (and the least). The narrative review of Schooler 1972 provides evidence that the impact of birth order is overstated, while Ernst and Angst 1983 is a well known review of the birth order literature from the 1940s to 1980 that suggests that birth order does not influence personality. Many of the studies it references later became part of Sulloway’s meta-analysis. Plomin, et al. 2001 revisits the role of non-shared environment in answering the question of why siblings are so different from each other with a behavioral genetics influence. Eckstein 2000 and Eckstein, et al. 2010 are influenced by the Adlerian perspective and focus mainly on studies that providence evidence for birth order differences in personality traits.

  • Eckstein, D. 2000. Empirical studies indicating significant birth-order related personality differences. Journal of Individual Psychology 56:481–494.

    A review of studies, largely published between 1960 and 1999, that provides support for birth order differences in personality. Includes studies that relate to traits of firstborns, middleborns, lastborns, and only children. Shows the range of study topics from conformity to narcissism. Illustrates greater research focus on firstborns historically.

  • Eckstein, D., K. J. Aycock, M. A. Sperber, et al. 2010. A review of 200 birth-order studies: Lifestyle characteristics. Journal of Individual Psychology 66:408–434.

    Gives Adlerian perspective and reviews Sulloway and his critics. Provides tables of characteristics by birth order (first/middle/last/only) and the statistically significant related studies from 1960–2010. Does not address non-significant study results, but an otherwise comprehensive reference.

  • Ernst, C., and J. Angst. 1983. Birth order: Its influence on personality. New York: Springer.

    Extensive review of birth order literature from 1946 to 1980. Concludes that effects are the result of poor research design, in particular failure to control for family size and socioeconomic status. Suggests that effects are found more often in studies that fail to control and are not found in ones with proper controls. The meta-analysis of Sulloway 1996 was a statistical counter to this paper.

  • Harris, J. R. 1998. The nurture assumption: Why children turn out the way they do. New York: Free Press.

    Argues that genes and peers shape personality more than parents (and by extension birth order) do and that, while parental love and attention are not distributed evenly and siblings do compete, these experiences do not translate into their relationships with non-kin. Focuses more on peers and socialization.

  • Plomin, R., K. Asbury, P. G. Dip, and J. Dunn. 2001. Why are children in the same family so different? Non-shared environment a decade later. Canadian Journal of Psychiatry 46:225–233.

    Behavioral genetics approach considers what aspects make up non-shared environment for siblings (parental favoritism, peers, interaction between genetics and environment). Plomin is one of first to highlight this question. Calls for more research and for consideration of role of chance. Available online for purchase or by subscription.

  • Schooler, C. 1972. Birth order effects: Not here, not now. Psychological Bulletin 78:161–175.

    DOI: 10.1037/h0033026

    Early narrative review of the literature on “normal” and psychiatric populations. Raises family size issues. No discussion of issues involved with using self-report of parental treatment of offspring. Studies are largely confined to comparing firstborns to lastborns or laterborns (everyone but firstborns), which is another issue not discussed (see Methodological Issues and Research Design). Available online for purchase or by subscription.

  • Sulloway, F. J. 1996. Born to rebel: Birth order, family dynamics, and creative lives. New York: Pantheon.

    Makes solid case for Darwinian theoretical approach to birth order focusing on differential parental investment and sibling competition. Documents personality differences and how they play out in terms of revolutions in science, religion, and politics. Highlights the rebellious role of the laterborn child.

  • Sulloway, F. J. 2010. Why siblings are like Darwin’s finches: Birth order, sibling competition, and adaptive divergence within the family. In The Evolution of Personality and Individual Differences. Edited by D. M. Buss and P. H. Hawley, 86–119. Oxford: Oxford Univ. Press.

    DOI: 10.1093/acprof:oso/9780195372090.001.0001

    Darwinian approach to birth order, personality divergence among siblings due to differential parental investment and sibling conflict. Focus on sibling niche picking and that sibling divergence is an adaptive strategy. Covers wide range of studies in review.

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