English

Alternative forms

• fraternal birth-order effect

Noun

fraternal birth order effect ‎(uncountable)

1. The scientific observation that a man's statistical probability of being homosexual increases with the number of older brothers he has.
   • 2008, Glenn Wilson & Qazi Rahman, Born Gay: The Psychobiology of Sex Orientation, Peter Owen (2008), ISBN 9780720613094, page 98:

     Thus the fraternal birth order effect is specific to male sexual orientation, and does not affect female sexual orientation.

   • 2010, Mark J. T. Sargeant, "Brain and Behaviour: Sex Differences", in Essential Psychology: A Concise Introduction (eds. Philip Banyard, Mark N. O. Davies, Christine Norman, & Belinda Winder), SAGE Publications (2010), ISBN 9781847875372, page 183:

     The influence of the fraternal birth order effect is not mediated by a male growing up with older stepbrothers but is influenced by them having biological brothers (who share the same mother) regardless of whether they are raised together or apart (Bogaert, 2006).

   • 2014, Tuck C. Ngun & Eric Vilain, "The Biological Basis of Human Sexual Orientation: Is There a Role for Epigenetics?", in Epigenetic Shaping of Sociosexual Interactions: From Plants to Humans (ed. Daisuke Yamamota), Academic Press (2014), ISBN 9780128002223, page 172:

     The fraternal birth order effect is one of the most replicated and robust findings in sexual orientation research. Each son increases the odds of homosexuality in the next son by 33% relative to the base population rate […]

   • For more examples of usage of this term, see Citations:fraternal birth order effect.