Fraternal Birth Order and the Maternal Immune Hypothesis of Male Homosexuality

2001 ◽  
Vol 40 (2) ◽  
pp. 105-114 ◽  
Author(s):  
Ray Blanchard
Keyword(s):  
Birth Order ◽  
Male Homosexuality ◽  
Maternal Immune Hypothesis ◽  
Fraternal Birth Order

Interaction of fraternal birth order and handedness in the development of male homosexuality

2006 ◽  
Vol 49 (3) ◽  
pp. 405-414 ◽  
Author(s):  
Ray Blanchard ◽  
James M. Cantor ◽  
Anthony F. Bogaert ◽  
S. Marc Breedlove ◽  
Lee Ellis
Keyword(s):  
Birth Order ◽  
Male Homosexuality ◽  
Fraternal Birth Order

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

2004 ◽  
Vol 36 (1) ◽  
pp. 51-59 ◽  
Author(s):  
WILLIAM H. JAMES
Keyword(s):  
Birth Order ◽  
Sexual Experience ◽  
Order Effect ◽  
Male Homosexuality ◽  
The Past ◽  
Older Brothers ◽  
Birth Order Effect ◽  
Fraternal Birth Order ◽  
Hormone Exposure ◽  
Fraternal Birth Order Effect

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.

AN ANTIBOY ANTIBODY? RE-EXAMINATION OF THE MATERNAL IMMUNE HYPOTHESIS

2007 ◽  
Vol 39 (6) ◽  
pp. 905-921 ◽  
Author(s):  
N. E. WHITEHEAD
Keyword(s):  
Birth Order ◽  
Fetal Brain ◽  
Brain Structures ◽  
Order Effect ◽  
Small Influence ◽  
Maternal Immune Hypothesis ◽  
Immune Attack ◽  
Fraternal Birth Order ◽  
Neurological Effects ◽  
Fraternal Birth Order Effect

SummaryThe maternal immune hypothesis (MIH) argues same sex attraction (SSA) results from maternal immune attack on fetal male-specific brain structures and involves the previous biological influence of elder brothers. One of the surveys supporting this is shown to be based on an unsuitable sample and to contain some strong contrary evidence. The hypothesis relies on at least four speculative ideas and there is evidence against each. (1) Likely immune response prevalence is too low compared with calculated SSA prevalence resulting from the fraternal birth order effect. (2) Testis immune attack would be more likely than brain attack but is not known. (3) Fetal brain structures are practically indistinguishable at birth and subsequent brain anatomical gender differentiation only occurs after birth when no attack is occurring. (4) The hypothesis also predicts unfavourable biology for late birth-order males but in fact the reverse is generally true, and neurological effects are very minor. Studies show aborted fetuses caused by likely maternal immune attack are predominantly girls rather than boys, which also argues against the theory. Studies on identical twins show that common factors such as uterine environment are only a small influence on SSA and post-natal idiosyncratic reactions and non-shared environmental factors are much larger influences.

scholarly journals BIRTH ORDER AND ANDROPHILIC MALE-TO-FEMALE TRANSSEXUALISM IN BRAZIL

2016 ◽  
Vol 49 (4) ◽  
pp. 527-535 ◽  
Author(s):  
Doug P. Vanderlaan ◽  
Ray Blanchard ◽  
Kenneth J. Zucker ◽  
Raffael Massuda ◽  
Anna Martha Vaitses Fontanari ◽  
...  
Keyword(s):  
Sexual Orientation ◽  
Birth Order ◽  
Order Effect ◽  
Present Sample ◽  
Older Brothers ◽  
Birth Order Effect ◽  
Maternal Immune Hypothesis ◽  
Fraternal Birth Order ◽  
Fraternal Birth Order Effect ◽  
Male To Female

SummaryPrevious research has indicated that biological older brothers increase the odds of androphilia in males. This finding has been termed thefraternal birth order effect. Thematernal immune hypothesissuggests that this effect reflects the progressive immunization of some mothers to male-specific antigens involved in fetal male brain masculinization. Exposure to these antigens, as a result of carrying earlier-born sons, is hypothesized to produce maternal immune responses towards later-born sons, thus leading to female-typical neural development of brain regions underlying sexual orientation. Because this hypothesis posits mechanisms that have the potential to be active in any situation where a mother gestates repeated male fetuses, a key prediction is that the fraternal birth order effect should be observable in diverse populations. The present study assessed the association between sexual orientation and birth order in androphilic male-to-female transsexuals in Brazil, a previously unexamined population. Male-to-female transsexuals who reported attraction to males were recruited from a specialty gender identity service in southern Brazil (n=118) and a comparison group of gynephilic non-transsexual men (n=143) was recruited at the same hospital. Logistic regression showed that the transsexual group had significantly more older brothers and other siblings. These effects were independent of one another and consistent with previous studies of birth order and male sexual orientation. The presence of the fraternal birth order effect in the present sample provides further evidence of the ubiquity of this effect and, therefore, lends support to the maternal immune hypothesis as an explanation of androphilic sexual orientation in some male-to-female transsexuals.

A FURTHER NOTE ON THE CAUSES OF THE FRATERNAL BIRTH ORDER EFFECT IN MALE HOMOSEXUALITY

2004 ◽  
Vol 36 (1) ◽  
pp. 61-62
Author(s):  
WILLIAM H. JAMES
Keyword(s):  
Birth Order ◽  
Sexual Experience ◽  
Order Effect ◽  
Male Homosexuality ◽  
Birth Order Effect ◽  
Fraternal Birth Order ◽  
Fraternal Birth Order Effect

I have recently written: ‘there seem likely to be causes common to male homosexuality and paedophilia. They may include sexual (or quasi-sexual) experience in childhood or adolescence’ (James, 2004). These words are rather vague and I wish to clarify them here.

scholarly journals A method yielding comparable estimates of the fraternal birth order and female fecundity effects in male homosexuality

2020 ◽  
Vol 287 (1923) ◽  
pp. 20192907 ◽  
Author(s):  
Ray Blanchard ◽  
Jurian Krupp ◽  
Doug P. VanderLaan ◽  
Paul L. Vasey ◽  
Kenneth J. Zucker
Keyword(s):  
Birth Order ◽  
Balancing Selection ◽  
Order Effect ◽  
Effect Estimate ◽  
Male Homosexuality ◽  
Female Fecundity ◽  
Older Brothers ◽  
Birth Order Effect ◽  
Fraternal Birth Order ◽  
Fraternal Birth Order Effect

The fraternal birth order effect (FBOE) is the finding that older brothers increase the probability of homosexuality in later-born males, and the female fecundity effect (FFE) is the finding that the mothers of homosexual males produce more offspring than the mothers of heterosexual males. In a recent paper, Khovanova proposed a novel method for computing independent estimates of these effects on the same samples and expressing the magnitude and direction of the effects in the same metric. In her procedure, only families with one or two sons are examined, and daughters are ignored. The present study investigated the performance of Khovanova's method using archived data from 10 studies, comprising 14 samples totalling 5390 homosexual and heterosexual subjects. The effect estimate for the FBOE showed that an increase from zero older brothers to one older brother is associated with a 38% increase in the odds of homosexuality. By contrast, the effect estimate for the FFE showed that the increase from zero younger brothers to one younger brother is not associated with any increase in the odds of homosexuality. The former result supports the maternal immune hypothesis of male homosexuality; the latter result does not support the balancing selection hypothesis.

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