Birth Order and Ratio of Brothers to Sisters in Spanish Transsexuals
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Three Western studies have shown that male-to-female (MF) homosexual transsexuals tend to be born later than their siblings and to come from sibships with more brothers than sisters. The objective of this study was to determine whether these variables would be replicated in 530 MF and female-to-male (FM) Spanish transsexuals according to sexual orientation. The results showed that MF homosexual transsexuals had significantly more older brothers than the non-homosexual MF group. Compared with the expected rates in the general population, birth order was significantly higher in both MF (Slater’s Index = 0.59; Fraternal Index = 0.61; Sororal Index = 0.58) and FM homosexual transsexuals (Slater’s Index = 0.65; Fraternal Index = 0.68; Sororal Index = 0.67), and sibling sex ratio was significantly higher than expected in homosexual MF (sex ratio = 0.55) but not in homosexual FM transsexuals. No significant differences were found in the non-homosexual subgroups. The replication of the later birth order and sibling sex-ratio effect in MF homosexual transsexuals corroborates previous findings in a variety of groups from different cultures and may suggest a common mechanism underlying the etiology of transsexualism.
KeywordsBirth order Sibling sex ratio Gender identity disorder Transsexualism Sexual orientation
This research was supported by grants SEJ2007-65686/PSIC, PI-0254/2007 JA, and MIG 238/2009.
- American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author.Google Scholar
- Cano, G., Bergero, T., Esteva, I., Giraldo, F., Gómez, M., & Gorneman, I. (2004). La construcción de la identidad de género en pacientes transexuales [Gender identity construction in transsexual patients]. Revista de la Asociación Española de Neuropsiquiatría, 90, 2840–2848.Google Scholar
- Esteva, I., Giraldo, F., Bergero, T., Cano, G., Crespillo, C., Ruíz, S., et al. (2001). Unidad de Trastornos de Identidad de Género de Andalucía: Evaluación diagnóstica, tratamiento hormonal y quirúrgico de los pacientes con Transexualidad [Gender Identity Disorder Unit in Andalusia: Diagnostic evaluation, hormonal, and surgical treatment in transsexual patients]. Cirugía Plástica Iberolatinamericana, 27, 259–324.Google Scholar
- Esteva, I., Gonzalo, M., Yahyaoui, R., Domínguez, M., Bergero, T., Giraldo, F., et al. (2006). Epidemiología de la transexualidad en Andalucía, atención especial al grupo de adolescents [Epidemiology of transsexualism in Andalusia: Special attention to the adolescent group]. Cuadernos de Medicina Psicosomática y Psiquiatría de Enlace, 78, 65–70.Google Scholar
- Gómez-Gil, E., & Esteva de Antonio, I. (2006). Ser transexual [Being transexual]. Barcelona: Editorial Glosa.Google Scholar
- VanderLaan, D. P., & Vasey, P. L. (2009). Male sexual orientation in independent Samoa: Evidence for fraternal order and maternal fecundity effects. Archives of Sexual Behavior. doi: 10.1007/s10508-009-9576-5.
- World Health Organization. (1993). International classification of diseases: Diagnostic criteria for research (10th ed.). Geneva: Author. Google Scholar