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THE CAUSE(S) OF THE FRATERNAL BIRTH ORDER EFFECT IN MALE HOMOSEXUALITY

Published online by Cambridge University Press:  05 January 2004

WILLIAM H. JAMES
WILLIAM H. JAMES
Affiliation:
The Galton Laboratory, University College London, Wolfson House, 4 Stephenson Way, London NW1 2HE
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Abstract

It has been established that the probability that a man is homosexual is positively related to his number of older brothers, but not older sisters when the brothers are accounted for. This is known as the ‘fraternal birth order’ effect. In the past, efforts have been made to explain this phenomenon in terms of several alternative biological hypotheses and a psychosocial hypothesis. This note examines how well these hypotheses accommodate the fraternal birth order effect. It is concluded that: (1) the evidence for the hypothesis of maternal immunoreactivity to the male fetus is weak; (2) the evidence for the intrauterine hormone exposure hypothesis is also weak; (3) the evidence for the hypothesis of postnatal learning is stronger. Lastly, there seem likely to be causes common to male homosexuality and paedophilia. They may include sexual (or quasi-sexual) experience in childhood or adolescence.

Type
Regular Articles
Information
Journal of Biosocial Science , Volume 36 , Issue 1 , January 2004 , pp. 51 - 59
Copyright
© 2004 Cambridge University Press

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