Birth order

From RationalWiki
Jump to navigation Jump to search
Tell me about
your mother

Icon psychology.svg
For our next session...
Popping into your mind

Birth order refers to a person's ordinal ranking among siblings — firstborn, second born, and so on. In pop psychology and the self-help movement, birth order is often said to have a profound, deterministic influence on personality, akin to the influence of the stars in astrology.

Some studies have found a correlation between birth order and IQ, but this is subject to debate, and the effect described is very small — 3 IQ points lower for the second born, and 1 point lower still for the third.[1] (The standard deviation on most IQ tests is around 15 points.) Among brothers, birth order is known to have a significant correlation with homosexuality, with every additional older brother increasing the incidence by 33%.[2]

Frank Sulloway of the University of California, Berkeley, who argues that birth order's effects on personality are significant, has found that openness to new ideas is strongly correlated with a higher order. Later-borns, he argues, accepted the theories of evolution and heliocentrism much more rapidly than firstborns, as well as discredited ideas like phrenology.[3] These findings have not been without controversy.[4]

While popular claims about birth order and personality often devolve into pseudoscience, the topic is also the subject of ongoing legitimate research.

External links[edit]


  1. Kristensen, Petter and Tor Bjerkedal. (22 June 2007). Explaining the Relation Between Birth Order and Intelligence. Science 316 (5832): 1717. DOI: 10.1126/science.1141493
  2. Blanchard, Ray. (September 2001). Fraternal birth order and the maternal immune hypothesis of male homosexuality. Hormones and Behavior 40 (2):105-14. PMID: 11534970
  3. Sulloway, Frank. (2001). Birth Order, Sibling Competition, and Human Behavior. In Harmon R. Holcomb, (Ed.), Conceptual Challenges in Evolutionary Psychology: Innovative Research Strategies. Dordrecht: Springer
    See also Shermer, Michael (2001). The Borderlands of Science: Where Sense Meets Nonsense. New York: Oxford University Press USA
  4. Harris, Judith R. (2006) No Two Alike: Human Nature And Human Individuality. New York: W.W. Norton