Are Sibship Characteristics Predictive of Same Sex Marriage? An Examination of Fraternal Birth Order and Female Fecundity Effects in Population-level Administrative Data from the Netherlands

Increased birth rank of homosexual males: disentangling the older brother effect and sexual antagonism hypothesis

“…We thus conclude that there is, to date, no conclusive support for an OSE in empirical data. The only exception is perhaps from Ablaza et al (2022), although their new regression method, using several highly correlated variables, requires a formal validation.…”

“…Secondly, an older sister effect (OSE) acting alongside the OBE has been described several times, e.g. in UK (King et al, 2005), Finland (Kangassalo et al, 2011), Samoa (VanderLaan and Vasey, 2011; Vasey and VanderLaan, 2007), Canada (Swift-Gallant et al, 2018), Netherlands (Ablaza et al, 2022), or in participants of a BBC internet survey (Blanchard and Lippa, 2020). Based on these findings, a recent meta-analysis proposed the presence of a pervasive OSE, in addition to the OBE (Blanchard et al, 2020a), even if this OSE is generally not as strong as the OBE.…”

Same-Sex Marriage and Common Mental Health Diagnoses: A Sibling Comparison and Adoption Approach

“…Based on known associations with both sexual orientation and mental health outcomes reported by prior research (Xu et al, 2018;Zietsch et al, 2012) and their availability in this cohort, parental age at birth, number of older brothers, older sisters, younger brothers, and younger sisters (0, 1, 2, and ≥ 3), and year of birth (1932-1939, 1940-1949, 1950-1959, 1960-1969, 1970-1979, 1980-1989, and 1990-1994) were included as potential confounding factors for the sibling comparison analysis. In the count of siblings, only full siblings and maternal half-siblings were counted given the known fraternal birth order effect in male sexual orientation (Bailey et al, 2016) and possibly in female sexual orientation (Ablaza et al, 2022). It is worth mentioning here that slightly different theoretical models are proposed for the male-versus-female finding.…”

I was born this way

“…The results show the influence of sex and number of siblings. For example, a man with three older brothers is 41% more likely to enter in a same‐sex union than if he had three older sisters, and that chance increases to 80% than if he has three younger brothers (Ablaza et al , 2022). “A biological basis for human sexuality suggests harmful practices like conversion therapy can’t alter someone’s sexual orientation.…”