Same-sex attraction in Iran appears to be concentrated within families, and is associated with a lower number of biological children in some groups, according to a study published in . human nature.
From an evolutionary perspective, same-sex sexual orientation has often been treated as a puzzle because it is directly associated with reduced reproduction, but it continues to emerge across cultures and historical periods. Previous research suggests that genetic factors contribute to same-sex attraction, and familial, twin, and molecular genetic studies indicate that same-sex attraction can persist within families.
However, much of this research has focused on European American samples, particularly cisgender gay men (men whose gender identity matches their assigned sex at birth), leaving large gaps in what is known about other cultural backgrounds and gender identities.
Mostafa Sadr Bazaz and colleagues examined this question in Iran, but there has been little empirical research examining whether same-sex attraction indicates family clustering or is associated with lower reproductive output. This study was motivated by the need to expand research beyond Western samples. By focusing on Iranian participants, the researchers were able to ask whether patterns documented in other groups also emerge in the Middle Eastern context, where social and cultural conditions surrounding sexuality and gender are vastly different.
The study included data from 1,534 Iranian adults recruited in three data collection activities from November 2021 to September 2024. Participants were recruited through online survey links distributed on platforms popular among Iranians such as X (formerly Twitter), Instagram, and Telegram. Through snowball sampling (current participants recruiting future participants from among their acquaintances) in Mashhad and Tehran. Through the Mashhad Gender Clinic. Through the researcher’s social network. From hospital staff and students. and from public social spaces such as coffee shops and shopping malls. Subsequent recruitment efforts also included online posters targeting Iranians of diverse sexualities and genders.
Participants reported their sex assigned at birth, their gender identity, whether they identify as transgender or transsexual, and their sexual attraction over the past 12 months using a 7-point Kinsey-type scale (ranging from completely heterosexual to completely homosexual). Based on participants’ reported gender identity and sexual attraction, they were divided into groups according to whether they were cisgender or transgender, male or female, and whether they were attracted to men, women, or both.
They also reported demographic information such as age, education (scored out of 7), and financial status (scored out of 5). To assess the occurrence of same-sex attraction in the family, participants indicated whether they had a brother, sister, nephew, niece, maternal or paternal female or male relative who was attracted to the same sex. They also reported whether they had children and how many biological and adopted children they had.
This finding provided evidence that same-sex attraction is concentrated in some families. For men, cisgender androphilic men (men who were assigned male at birth and are attracted to men) were more likely to report having at least one same-sex attracted male relative on both the maternal and paternal sides of the family than cisgender gynophilic men (men who were assigned male at birth and are attracted to women). However, this study found no significant group differences in the proportion of brothers and sisters who were attracted to the same sex among male participants.
For women, cisgender bisexual women (women who were assigned female at birth and are attracted to both sexes) reported more sisters who were attracted to the same sex than cisgender androtropic women. Also, cisgender bisexual and cisgender gynophilic women were more likely than cisgender androphilic women to report having a same-sex attracted female relative on their maternal side of the family.
Findings regarding reproductive output were clearer for men than for women. Cisgender gynophilic men reported more biological children than cisgender androgynous men, transgender androgynous men, and cisgender androgynous men. In other words, men’s same-sex attraction and bisexual attraction were associated with having fewer biological children.
Among women, overall group differences were weaker. Only transgender gynecophilic women had significantly fewer biological children than cisgender androphilic women. Cisgender gynophilic women and cisgender hermaphrodite women did not differ significantly from cisgender androtropic women in producing offspring.
Of note, the sample may not be representative as the participants were generally young, educated, and relatively well-off, and many were recruited from Tehran and Mashhad through network-based methods. Some groups, particularly those of cisgender gynophilic women, were unequal or small, which may have limited the study’s ability to detect some effects.
Overall, the results of this study suggest that familial clustering and reduced reproductive output associated with same-sex attraction are not limited to Western samples, and also show that these patterns may vary by gender, gender identity/expression, and kinship lineage.
The study, “The Paradox of Same-Sex Sexual Orientation: Evidence of Increased Familial Incidence and Decline in Reproductive Output in Iran,” was authored by Mostafa Sadr-Bazaz and Paul L. Basie.
