In June 2006, Anthony Bogaert released a study in the Proceedings of the National Academy of Science which created a world wide buzz about a possible biological basis for the same-sex attraction of some men.
A recent Journal of Biosocial Science article by Neil Whitehead takes on this hypothesis and finds several problems. I don’t have time for a detailed analysis at this time (I am behind on as it is on these – notably on the Witelson brain study), but I do want to get this on the radar. Here is his concluding section:
An antiboy antibody? Unlikely. Gooren (2006), in his review on psychosexual development, bluntly concludes ‘The biological basis advanced for the fraternal birth order hypothesis lacks any experimental support’. The present paper argues further that there is a significant weight of evidence against the MIH, whatever the explanation of the FBO [fraternal birth order] effect may be. The MIH was an intellectually clean and satisfying explanation for the FBO effect, and its original authors are to be commended. However, present evidence is for alloimmune reactions being probably too rare to account for the SSA prevalence observed, no support for macrostructural-level attack, unlikely attack on brain if not on testes, no MIH-related lower birth weight, healthier late-birth-order males. At the least, any modification of the MIH would demand serious consideration of the apparent disproportionate deaths of female fetuses during immune attack. One might sincerely hope that any revised theory will be simpler than the present one – which in any case attempts to account for only 17% of SSA.
The very division of SSA into FBO origin and other more major origins seems to raise difficulties. Twin study conclusions are challenging because they simultaneously dispose of most biological and social reasons for SSA; erratic and individualistic causes should predominate.
Because of the erratic nature of SSA in later-birth-order boys, even an acceptance of the MIH would seem to demand an acceptance of a principle that something akin to chance predominates.
This is close to my current view of orientation development on the whole – not terribly satisfying, but an honest appraisal of the research as it is. Note this is an assessment of the development of SSA and says nothing about how changeable it might be. Nothing here relates to women either. As an aside, I have been reading some research which suggests that the erotic orientation of men becomes more channelized than for women; meaning that in brain scans, for instance, men show very specific reactions to their preferred object of sexual attraction, whereas, women more frequently demonstrate sexual arousal to images of both gender.