• Corpus ID: 27007732

Fraternal Birth Order and the Maternal Immune

  title={Fraternal Birth Order and the Maternal Immune},
  author={Ray Blanchard},
increasing the odds of homosexuality by approximately 33%. It has been hypothesized that this fraternal birth order effect reflects the progressive immunization of some mothers to Y-linked minor histocompatibility antigens (H-Y antigens) by each succeeding male fetus and the concomitantly increasing effects of such maternal immunization on the future sexual orientation of each succeeding male fetus. According to this hypothesis, anti-H-Y antibodies produced by the mother pass through the… 

Figures and Tables from this paper

Sibling Sex Ratio and Birth Order in Early-Onset Gender Dysphoric Adolescents
The results for the male probands were consistent with prior speculations that a high fraternal birth order is found in all homosexual male groups, but an elevated sibling sex ratio is characteristic of gender dysphoric homosexual males.
Family and Sexual Orientation: The Family-Demographic Correlates of Homosexuality in Men and Women
Using a nationally representative sample of young adults, the maternal immune hypothesis, which posits that the only biodemographic correlate of male homosexuality is the number of older brothers, is tested, and it is found that having one older brother does not raise the likelihood of homosexuality.
Sexual selection and sex differences in the prevalence of childhood externalizing and adolescent internalizing disorders.
  • M. Martel
  • Psychology, Biology
    Psychological bulletin
  • 2013
A metatheoretical framework is provided to help integrate prior ideas about sex differences and can also generate new predictions of sex differences in markers, etiology, mechanisms, and developmental timing of common forms of psychopathology.
Is Homosexuality a Paraphilia? The Evidence For and Against
  • J. Cantor
  • Psychology
    Archives of sexual behavior
  • 2012
The present article examined the question of homosexuality by comparing the major correlates and other features of homosexuality and of the paraphilias, including prevalence, sex ratio, onset and course, fraternal birth order, physical height, handedness, IQ and cognitive neuropsychological profile, and neuroanatomy.


H-Y antigen and homosexuality in men.
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.
Results are consistent with the hypothesis that the high birth order of homosexual men reflects the progressive immunization of certain mothers to H-Y antigen by succeeding male fetuses, and the increasing effects of H- Y antibodies on sexual differentiation of the brain in succeeding male Fetuses.
Fraternal Birth Order and Sexual Orientation in Pedophiles
It is shown that fraternal birth order correlates with homosexuality in pedophiles, just as it does in men attracted to physically mature partners, and may prove the first identified universal factor in homosexual development.
The results confirmed earlier reports thatboys with older brothers weigh less at birth than boys with older sisters, but they did not confirm reports that girls with olderbrothers weigh less than girls with younger sisters.
The relation of closed birth intervals to the sex of the preceding child and the sexual orientation of the succeeding child.
The study investigated whether homosexual men are, on average, born a shorter time after their next-older siblings than are heterosexual men, and showed that birth interval was negatively correlated with sibship size, positively correlated with maternal age, and uncorrelated with paternal age.
Birth order and ratio of brothers to sisters in transsexuals
  • R. Green
  • Psychology
    Psychological Medicine
  • 2000
Hypotheses explaining the extension of prior findings to this large sample of transsexual males include a progressive maternal immunization to the male foetus either through the H-Y antigen or protein-bound testosterone or alterations in foetal androgen levels in successive pregnancies, all modifying male psychosexual development.
Birth order and sibling sex ratio in homosexual male adolescents and probably prehomosexual feminine boys.
The purpose of this study was to extend the findings, previously limited to adults, that male homo sexuals have a greater than average proportion of male siblings and a later than average birth
How Many Gay Men Owe Their Sexual Orientation to Fraternal Birth Order?
This work derived generalized forms of two epidemiological statistics, the attributable fraction and the population attributable fraction, which quantify the relationship between a condition and prior exposure to an agent that can cause it and showed that roughly 1 gay man in 7 owes his sexual orientation to the fraternal birth order effect.
Birth order and male homosexuality: extension of Slater's index.
Homosexual men tend to be later-born children. Slater's index, the ratio of older sibs to all sibs, is consistently higher for male homosexuals than for comparable heterosexuals. According to some