Gay siblings statistics

Fraternal birth order, also known as the older brother effect, has been correlated with male sexual orientation, with a significant volume of research finding that the more older brothers a male has from the same mother, the greater the probability he will have a homosexual orientation. If you have five older brothers, your chance of being gay is about 8% — so, four times the baseline probability. 39% of siblings of gay individuals have changed their perceptions and attitudes toward LGBTQ+ rights after their sibling came out, indicating influence and awareness.

Specifically, men with one older brother are 12% more likely to enter a same-sex union than men with one older sister, and 21% more likely than men with just one younger brother or sister. In several studies comparing gender dysphoric youth, who are likely to be homosexual in adulthood, to clinical or non-clinical control groups, the findings have been consistent with the fraternal birth order effect in males; however, less is known about unique sibship characteristics of gender dysphoric females.

New research shows having a greater number of older brothers increases the probability of a person entering a same-sex union at some point in their lives. This finding, detailed in our paper published today in the Journal of Sex Research, offers a rare insight into the origins of sexual orientation. But despite these encouraging developments, sexual minorities still experience high levels of stigma — and the origins of sexual orientation remain a matter of debate.

For example, we know people who view sexual orientation as a product of biological factors such as hormones or genetics are more likely to support sexual minorities and their civil rights, compared to those who view it as a product of social factors or individual choice. These maternal antibodies accumulate over successive pregnancies with male foetuses, which means men with more older brothers are more likely to experience same-sex sexual attraction.

However, previous research documenting the fraternal birth order effect has relied on small and selective participant samples, which has led some scholars to question the authenticity of the phenomenon. Indeed, no study of a representative population sample has supported its existence — until now. Our research used unique data from Dutch population registers.

These data allowed us to follow the life trajectories of more than nine million people born between and This time, we used it to provide a robust test of the fraternal birth order effect. We used this information as a proxy for homosexuality. In the Netherlands, registered same-sex partnerships have been recognised since , and same-sex marriage since Our results show clear evidence of a fraternal birth order effect on homosexuality.

The birth order and total number of siblings matter too.

gay brothers in a relationship

Men who are the youngest sibling are more likely to enter a same-sex union than men who are the oldest sibling, and the differences grow larger as the total number of siblings increases. The chart below illustrates some of our findings, showing the number of men who entered same-sex unions among those with up to three siblings. The sex of older siblings wields a considerable influence over same-sex union formation.

On the other hand, the sex of younger siblings plays little to no role. Unlike earlier studies which focused almost exclusively on men, we documented the same pattern of results among women. We found women are also more likely to enter a same-sex union if they have older brothers. But unfortunately, these issues still loom large in contemporary debate, further highlighting the importance of our findings.

We acknowledge the diverging opinions on the value of research concerning the origins of human sexuality. Some feel such research is irrelevant because the findings should have no bearing on public attitudes or legislation, while others reject it for more hostile reasons. Like others before us , we consider this research essential. Understanding the mechanisms behind sexual orientation can offer insights into what makes people who they are, and helps normalise the full spectrum of human sexual diversity.

Read more: Why has same-sex sexual behaviour persisted during evolution? Christine Ablaza does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.