Sexual orientation, fraternal birth order, and the maternal immune hypothesis: A review

@article{Bogaert2011SexualOF,
  title={Sexual orientation, fraternal birth order, and the maternal immune hypothesis: A review},
  author={Anthony F Bogaert and Malvina N Skorska},
  journal={Frontiers in Neuroendocrinology},
  year={2011},
  volume={32},
  pages={247-254}
}
Fraternal birth order effect on sexual orientation explained
  • J. Balthazart
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  • 2017
TLDR
Direct biochemical evidence is presented indicating that the increased incidence of homosexuality in males with older brothers results from a progressive immunization of the mother against a male-specific cell-adhesion protein that plays a key role in cell–cell interactions during development called neuroligin 4 Y-linked, or NLGN4Y.
Male homosexuality and maternal immune responsivity to the Y-linked protein NLGN4Y
TLDR
This study conducted a direct test of an immunological explanation of the finding that gay men have a greater number of older brothers than do heterosexual men, and suggested an association between a maternal immune response to NLGN4Y and subsequent sexual orientation in male offspring.
BIRTH ORDER AND ANDROPHILIC MALE-TO-FEMALE TRANSSEXUALISM IN BRAZIL
TLDR
The presence of the fraternal birth order effect in the present sample provides further evidence of the ubiquity of this effect and lends support to the maternal immune hypothesis as an explanation of androphilic sexual orientation in some male-to-female transsexuals.
Gay Male Only-Children: Evidence for Low Birth Weight and High Maternal Miscarriage Rates
TLDR
This study found further support for a distinct pattern of maternal immune response implicated in the etiology of male sexual orientation, and Mechanisms that may underlie this potential second type of maternalimmune response are discussed.
The Association Between Fraternal Birth Order and Anal-Erotic Roles of Men Who Have Sex with Men
  • C. Wampold
  • Psychology
    Archives of sexual behavior
  • 2018
TLDR
Late fraternal birth order was correlated with receptive anal-erotic behavior among MSM, and Bottoms had a significantly greater mean number of older brothers than did Not-Bottoms.
Increased birth rank of homosexual males: disentangling the older brother effect and sexual antagonism hypothesis
TLDR
Support for OBE was apparent in aggregated data, with the OBE increasing linearly with fertility, and an additional older sister effect (OSE) seemed to result from a sampling bias in presence of OBE, and is likely to be artefactual.
Minireview: Hormones and human sexual orientation.
TLDR
It seems therefore that the prenatal endocrine environment has a significant influence on human sexual orientation but a large fraction of the variance in this behavioral characteristic remains unexplained to date.
The relationship between fraternal birth order and childhood sex-atypical behavior among the Istmo Zapotec muxes.
TLDR
The results indicated that both cisgender muxe nguiiu and transgender muxe gunaa were more likely to be later born among brothers than gynephilic men, but the number of older brothers did not differentiate between transgender and cisgendermuxes, nor did it predict CSAB among muxes.
Alternative Sexual Orientation in Humans: What Is Known and What Needs to Be Known Further
TLDR
This review tries to explain why natural selection is not eliminating the genetic factors associated with homosexuality even at the cost of the evolutionary fitness of homosexual individuals.
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This study employed a larger, independent replication sample of fa’afafine and gynephilic males from Independent Samoa to suggest that fraternal birth order and maternal fecundity effects both exist in Samoa.
Review and theory of handedness, birth order, and homosexuality in men
TLDR
The maternal immune hypothesis might be extended or modified to account for the apparent interaction of older brothers and handedness, and two possibilities are considered: non- right-handed foetuses are insensitive to the presence of maternal anti-male antibodies, and mothers of non-right-handedfoetuses do not produce anti- male antibodies.
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TLDR
A direct test pitting prenatal against postnatal mechanisms strongly suggests a prenatal origin to the fraternal birth-order effect in men, regardless of the amount of time reared with these siblings.
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A comprehensive review and critique of biological research on sexual orientation published over the last decade is provided, including measurement issues, cognitive, and psychophysiological issues, and lack of research on women.
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TLDR
This finding suggests that the mechanism by which older brothers increase the odds of homosexuality in later-born males operates prior to the individual's birth, and hypothesize that this mechanism may be immunologic, that antimale antibodies produced by human mothers in response to immunization by male fetuses could decrease the birth weight of subsequentmale fetuses as well as increase their odds of homosexuals.
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TLDR
The results suggest that the mechanism underlying the fraternal birth order phenomenon has an effect on physical development that lasts and is detectable into adulthood (i.e., adult stature), which is most likely to occur in men with a high number of older brothers and shorter stature.
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TLDR
This hypothesis is consistent with a variety of evidence, including the apparent irrelevance of older sisters to the sexual orientation of later-born males, the probable involvement of H-Y antigen in the development of sex-typical traits, and the detrimental effects of immunization of female mice to H- Y antigen on the reproductive performance of subsequent male offspring.
Sexual orientation and handedness in men and women: a meta-analysis.
TLDR
The results support the notion that sexual orientation in some men and women has an early neurodevelopmental basis, but the factors responsible for the handedness-sexual orientation association require elucidation.
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