Birth Order and Ratio of Brothers to Sisters in Spanish Transsexuals

Abstract

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.

Sibling Sex Ratio and Birth Order in Early-Onset Gender Dysphoric Adolescents

“…To our knowledge, 12 studies have investigated birth order and/or sibling sex ratio among gender dysphoric individuals (or their closest equivalents in non-Western cultures). Nine of these studies looked at differences in birth order and sibling sex ratio between “homosexual” and “non-homosexual” transsexual adults (Blanchard & Sheridan, 1992; Blanchard, Zucker, Cohen-Kettenis, Gooren, & Bailey, 1996; Gomez-Gil et al, 2011; Green, 2000; Poasa, Blanchard, & Zucker, 2004; Tsoi, Kok, & Long, 1977; VanderLaan & Vasey, 2011; Vasey & VanderLaan, 2007; Zucker, Blanchard, Kim, Pae, & Lee, 2007) (instead of “homosexual” transsexuals, we will refer to male-to-female transsexuals sexually attracted to men as androphilic MtFs, and to female-to-male transsexuals sexually attracted to women as gynephilic FtMs). Overall, these studies found an excess of brothers in the androphilic MtFs groups but not in the non-androphilic transsexual male groups.…”

Birth Order and Sibling Sex Ratio in Relation to Sexual Orientation in China

“…We believe that it is interesting that this effect has been observed in gender dysphorics , as well as transsexuals (Gómez-Gil et al, 2011;Zucker et al, 2007). However, to date, the researchers of birth order and sibling sex ratio in relation to sexual orientation have predominantly limited their studies to Western populations.…”

The Palgrave Handbook of the Psychology of Sexuality and Gender

“…There is a growing body of evidence which shows that key biological factors are involved in the development of a gender identity which differs from that assigned at birth (Garcia-Falgueras & Swaab, 2008;Gómez-Gil et al, 2011;Hare et al, 2009;Kruijver et al, 2000;Rametti et al, 2011;Simon et al, 2013;Zhou et al, 1995). It is also well established that psychological, social, and cultural factors play a role in the expression of gender, and likely in many instances in its formation (e.g.…”