BIRTH ORDER AND ANDROPHILIC MALE-TO-FEMALE TRANSSEXUALISM IN BRAZIL.
Previous research has indicated that biological older brothers increase the odds of androphilia in males. This finding has been termed the fraternal birth order effect. The maternal immune hypothesis suggests 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.
*Department of Psychology,University of Toronto Mississauga,Mississauga,Ontario,Canada.
Doug P
DP
Vanderlaan
‡Department of Psychiatry,University of Toronto,Toronto,Ontario,Canada.
Ray
R
Blanchard
‡Department of Psychiatry,University of Toronto,Toronto,Ontario,Canada.
Kenneth J
KJ
Zucker
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Raffael
R
Massuda
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Anna Martha Vaitses
AMV
Fontanari
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
André Oliveira
AO
Borba
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Angelo Bradelli
AB
Costa
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Maiko Abel
MA
Schneider
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Andressa
A
Mueller
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Bianca Machado Borba
BMB
Soll
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Karine
K
Schwarz
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Dhiordan Cardoso
DC
Da Silva
§Gender Identity Program-PROTIG,Hospital de Clinicas de Porto Alegre,Rio Grande do Sul,Porto Alegre,Brazil.
Maria Inês Rodrigues
MIR
Lobato
D000328:Adult; D001722:Birth Order; D001938:Brazil; D005783:Gender Identity; D006801:Humans; D008297:Male; D057228:Masculinity; D008875:Middle Aged; D012725:Sexual Behavior; D014189:Transsexualism / Q000453:epidemiology* / Q000523:psychology*; D055815:Young Adult