Where sexual orientation comes from (research on causes)
What research has found about why some people are attracted to the same sex, to more than one sex or to the other sex. The picture is of many small influences: genes with tiny effects each, likely prenatal factors, and experiences that differ even between twins raised together. No single cause has been found, and the major review found no support for the idea that parenting or other social learning produces it.
What drives it
The question usually comes up for a reason: a parent wondering what they did, a person hoping a cause would make them legitimate or changeable, a believer weighing choice and sin. The research answers less than each of them hopes. It finds genetic and likely prenatal influences, which nobody chooses, and it can’t trace any one person’s orientation to a cause. For identification it helps separate what the studies say from what each side wants them to say.
How it shows
Work
A colleague sharing a headline about a ‘gay gene’, and the argument that follows. A teacher asked by a parent whether a club or a friend group made their son gay.
Relationships
A mother going over her son’s childhood for the moment she got it wrong. A father blaming an uncle or a school. A gay sibling and a straight sibling raised in the same house the same way.
Self
Notice what you hope a cause would prove, and to whom.
What tells it apart
Sexual fluidity (Diamond): Origins research asks what shapes orientation in the first place. Fluidity research asks how attraction moves over a life. An orientation can have early roots and still shift.
Parental guilt (‘mom guilt’): Parental guilt is a general sense of having failed a child. A parent searching for what caused a child’s orientation may be feeling it, and the research offers no grounds for blaming parents.
Conversion therapy (sexual orientation and gender identity change efforts): The belief that orientation comes from upbringing or a wound has been used to justify change efforts. The research on causes found no support for social causes, and the APA review found insufficient evidence that change efforts work.
A test
Ask the person what answer they hope the research gives, and what it would change for them. If the hope is to assign blame, prove legitimacy or open a door to change, the research may be carrying more than it can, since it describes populations and can’t explain one person.
Questions to carry
- When I ask what caused it, what am I hoping the answer will let me do?
- What would change in how I see myself, or my child, if there were no answer at all?
How strong the research is
moderate. Twin studies find a moderate genetic share. Among 3,826 adult twin pairs in Sweden (Långström and colleagues, Archives of Sexual Behavior, 2010), genes explained about 34 to 39% of the variation in same-sex behavior in men and 18 to 19% in women, the shared family environment none in men and 16 to 17% in women, and the rest came from experiences unique to each twin, social and biological, with wide margins of error. A genome study of 477,522 people (Ganna and colleagues, Science, 2019) found five genetic markers linked to ever having had a same-sex partner and estimated that all measured variants together explained 8 to 25% of the variation, with no single gene and no way to predict one person’s behavior. Critics said ‘ever had a same-sex partner’ is a crude stand-in for orientation, and the authors replied that it overlapped with finer measures of attraction and identity. A review by Bailey and colleagues (Psychological Science in the Public Interest, 2016) concluded that the findings do not support orientation being taught or learned through social means, and found little evidence that it becomes more common as societies grow more tolerant. The fraternal birth order effect, more older brothers raising the odds of being gay in men, is disputed: a 2021 preprint review (Vilsmeier and colleagues) found no valid evidence, and a study of Dutch population records (Ablaza and colleagues, 2022) found it in both men and women.
Where it comes from
J. Michael Bailey, Paul Vasey, Lisa Diamond, S. Marc Breedlove, Eric Vilain and Marc Epprecht, ‘Sexual orientation, controversy, and science’, Psychological Science in the Public Interest, 2016. Andrea Ganna and colleagues, ‘Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior’, Science, 2019