Sex Male Gay

Schematic illustration of how pregnant women might mount a progressive immune response to the male-linked protein NLGN4Y during the gestation of male, but not female, embryos (A). The accumulation of anti-NLGN4Y antibodies (B) would then increase the relative incidence of a gay orientation among subsequent sons (C). Note, however, that this mechanism potentially explains only a fraction of gay males, so other mechanisms must also be at work.

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In fact, there is a progressive increase of anti-NLGN4Y antibodies across groups of mothers: women with no sons

The Bogaert et al. (3) report also provides additional support for biological theories of sexual orientation. Note that the FBO effect accounts for only a maximum of 29% of gay males, or possibly a bit more if one assumes that a fraction of the primiparous mothers who

In PNAS, Bogaert et al. present direct biochemical evidence indicating that the increased incidence of homosexuality in males with older brothers results from a progressive immunization of the mother against a malespecific cell-adhesion protein

had a gay son had unknowingly miscarried male embryos previously (12). Similarly, the other biological mechanisms implicated in the control of sexual orientation, the effects of early steroid hormones, and genetic background, also explain only a fraction of the cases of male homosexuality (6). Whether a unifying theory can be derived from the available experimental evidence thus remains unclear and will require additional investigations. Either the diverse biological mechanisms (hormonal, genetic, and immune) each explain a fraction of the cases and homosexuality is a multifactorial phenotype that can have multiple independent origins, or these different mechanisms interact and complement each other to control a phenotype that is otherwise essentially homogeneous. The endocrine and genetic mechanisms can easily be seen as interacting; for example, if a genetic mutation or variant affects the secretion or action of sex steroids in the brain. A gay orientation in males has been linked to the terminal Xq28 region of the X chromosome (8, 9), and this region contains a gene coding for protein MAGE-11 (melanoma-associated antigen), which is a coactivator of the androgen receptor (13). A mutation of this gene in males could thus modify testosterone action during brain development, although such an interaction still raises a number of questions (14). An interaction between the immune mechanisms discussed here and the endocrine or genetic mechanisms is less obvious, but not inconceivable.

Individuals who identify as male and have had sex with another man within the past 3 months will be deferred under the MSM policy. Learn more about MSM blood donation criteria. Further questions may be directed to the Donor and Client Support Center at 1-866-236-3276.

Individuals who identify as female and have sex with a man, may be eligible to donate blood, if all other blood donation eligibility criteria are applicable. If an individual was previously deferred from donating blood due to MSM, that person will need to call the Donor and Client Support Center at 1-866-236-3276 to confirm eligibility before coming to donate. Additional eligibility questions may also be answered through the Donor and Client Support Center.

a Adult and adolescent men aged 13 and older.b Based on sex at birth and includes transgender people.c HIV diagnoses refers to the number of people who received an HIV diagnosis during a given time period, not when the people got HIV infection.d Unless otherwise noted, the term United States (US) includes the 50 states, the District of Columbia, and the 6 dependent areas of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, the Republic of Palau, and the US Virgin Islands.e The term male-to-male sexual contact is used in CDC surveillance systems. It indicates a behavior that transmits HIV infection, not how individuals self-identify in terms of their sexuality. This fact sheet uses the term gay and bisexual men.f Includes infections attributed to male-to-male sexual contact and injection drug use (men who reported both risk factors).

Secondly, the fraternal birth order effect operates through a biological mechanism during prenatal life, not during childhood or adolescence.[11] Direct evidence for this is the fact that the fraternal birth order effect has been found even in males not raised with their biological brothers, and biochemical evidence was found in a lab study in 2017.[1] It has been determined that biological brothers increase the odds of homosexuality in later-born males even if they were reared in different households, whereas non-biological siblings, such as step-brothers or adopted brothers, have no effect on male sexual orientation.[7]Indirect evidence also indicates that the fraternal birth order effect is prenatal and biological in nature rather than postnatal and psychosocial: The fraternal birth order effect has been confirmed to interact with handedness,[23][11] as the incidence of homosexuality correlated with an increase in older brothers is seen only in right-handed males.[22][24][25][23] Since handedness develops prenatally,[26] this finding indicates that prenatal mechanisms underlie the fraternal birth order effect.[11] It has also been found that homosexual males with older brothers have significantly lower birth weights compared to heterosexual males with older brothers.[27][28] As birth weight is undeniably prenatally determined, it is known that a common developmental factor that operates before birth necessarily underlies the fraternal birth order effect and male sexual orientation.[29]

In a 2017 study, researchers found an association between a maternal immune response to neuroligin 4 Y-linked protein (NLGN4Y) and subsequent sexual orientation in their sons. NLGN4Y is important in male brain development; the maternal immune reaction to it, in the form of anti-NLGN4Y antibodies, is thought to alter the brain structures underlying sexual orientation in the male fetus. The study found that women had significantly higher anti-NLGN4Y levels than men. The result also indicates that mothers of gay sons, particularly those with older brothers, had significantly higher anti-NLGN4Y levels than did the control samples of women, including mothers of heterosexual sons.[38]

The fraternal birth order effect is a phenomenon that can be described in one of two ways:[39] Older brothers increase the odds of homosexuality in later-born males or, alternatively, homosexual men tend to have more older brothers than do heterosexual men.[13][40][11] It has been found that the proportion of older brothers (i.e., .mw-parser-output .sfracwhite-space:nowrap.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tiondisplay:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center.mw-parser-output .sfrac .num,.mw-parser-output .sfrac .dendisplay:block;line-height:1em;margin:0 0.1em.mw-parser-output .sfrac .denborder-top:1px solid.mw-parser-output .sr-onlyborder:0;clip:rect(0,0,0,0);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1pxOlder Brothers/All Siblings) is 31% greater in the sibships of homosexual males than in the sibships of heterosexual males.[13] Alternatively, the ratio of older brothers to other siblings (i.e., Older Brothers/Other Siblings) is 47% greater for homosexual males than it is for heterosexual males.[13]

In a few studies, homosexual subjects have occasionally displayed both a larger number of older brothers and a larger number of older sisters in comparison to heterosexual men. This is because a person's number of older brothers and number of older sisters tend to be positively correlated. So, if Proband A has more older brothers than Proband B, chances are that Proband A also has more older sisters than Proband B.[41][33] These findings of excess of older sisters are hence occasional by-products of homosexual men having an excess of older brothers, are not found as consistently as the excess of older brothers, and thus need not detract from the significance of the fraternal birth order effect.[33][42] When samples are drawn from populations with relatively high fertility rates, the positive correlation between number of older brothers and older sisters may give the false impression that both the number of older brothers and the number of older sisters are associated with male sexual orientation. Indeed, two samples from the high fertility Samoan population displayed simultaneous fraternal and 'sororal' birth order effects. However, direct comparison of the magnitudes of these two effects showed that the fraternal birth order effect took precedence in the studies.[31][33] Various studies and meta-analyses have confirmed that only the older brother effect is consistently associated with homosexuality:[40][33]

The fraternal birth order effect is independent of potential confounding factors such as age, year of birth, and socioeconomic status.[11] It has also been found that the fraternal birth order effect can be demonstrated whether the homosexual and heterosexual groups being compared on older brothers both have large or small family sizes, so long as both groups have the same family size (or can be adjusted to simulate that condition).[13] Additionally, to detect the fraternal birth order effect, it is necessary that family size of homosexual and heterosexual groups are not strongly affected by the various parental strategies (so-called 'stopping rules') of ceasing reproduction after one child, after one male child, or after a child of each sex, because in these particular situations, neither homosexual nor heterosexual males have enough older brothers to make comparisons meaningful. For example, a study done in mainland China did not find any fraternal birth order effect, which the authors attributed to the one-child policy.[13][22][44][45][46] 041b061a72