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A Possible Second Type of Maternal–Fetal Immune Interaction Involved in Both Male and Female Homosexuality

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Abstract

Recent research has found that the mothers of firstborn homosexual sons produce fewer subsequent offspring than do the mothers of firstborn heterosexual sons. It was hypothesized that a subset of mothers of firstborn homosexuals may be responsible for this finding. If there is a subset of mothers whose immune reactions cause their first male fetus to be homosexual and their subsequent fetuses to die, then their immune reactions should also cause their first male fetus to have a lower birth weight. This leads to the prediction that, within the population of firstborn homosexual men, those with no younger siblings should also tend to have lower birth weights. This prediction was tested using a previously published sample of 1,445 firstborn subjects: 929 heterosexual females, 47 homosexual females, 409 heterosexual males, and 60 homosexual males. The results showed that firstborn homosexuals with no younger siblings (i.e., only children) did have lower birth weights compared with all the other subjects, but the finding applied to firstborn lesbian women as well as firstborn gay men.

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Notes

  1. It might be noted that the assumption that a firstborn homosexual male could not owe his sexual orientation to a maternal immune response could have been challenged without the study by Blanchard (2011) or the present study, and without the notion of a second type of maternal–fetal immune interaction. There was always the remote but theoretical possibility that environmental antigens could mimic human male-specific antigens and thus raise anti-male antibodies in a woman before she ever became pregnant with a male fetus. Thus, firstborn homosexual men could also be the result of maternal immunization. A known model for this hypothetical scenario would be the immunization of blood group O mothers by A-antigens or B-antigens of environmental origin, resulting in anti-A or anti-B antibodies, which sometimes pass through the placenta and affect fetuses with blood groups A or B.

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  1. Department of Psychiatry, University of Toronto, 250 College St., Toronto, ON, M5T 1R8, Canada

    Ray Blanchard

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  1. Ray Blanchard
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Correspondence to Ray Blanchard.

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Blanchard, R. A Possible Second Type of Maternal–Fetal Immune Interaction Involved in Both Male and Female Homosexuality. Arch Sex Behav 41, 1507–1511 (2012). https://doi.org/10.1007/s10508-011-9896-0

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  • DOI: https://doi.org/10.1007/s10508-011-9896-0

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