Why am I gay?

Episode Summary

Executive Summary: The episode answers listener Ahmed’s question, “Why am I gay?” by explaining that sexual orientation appears to arise from a mix of genetic predisposition, prenatal environment, and developmental variation—not parenting. Experts discuss twin studies, a “loaded dice” model of genes, fraternal birth order effects, and indirect hormone markers, while also noting that no single cause explains any one person’s sexuality.

Main Topics: Sexual orientation as a genetic probability, not a single gene (Priority: 5/5): Geneticist Kevin Mitchell argues against a single “gay gene” and says many genes likely influence sexuality by shaping probabilities rather than fixed outcomes. Developmental variation and the “loaded dice” analogy (Priority: 5/5): The show explains that identical genes do not produce identical people because development is noisy; genes load the dice, but the developmental process determines the final outcome. Prenatal environment and the fraternal birth order effect (Priority: 4/5): Dr. Melvina Skorska describes evidence that gay men, on average, have more older brothers, likely due to a maternal immune response during male pregnancies. Hormonal influences in the womb (Priority: 4/5): The episode discusses indirect evidence that atypical prenatal androgen exposure may influence sexuality, including finger-length ratios as a proxy measure. Parenting and nurture as a cause of sexuality (Priority: 5/5): Lisa Diamond strongly rejects the idea that distant or absent parents cause someone to be gay, distinguishing parenting from broader environmental influences. Evolutionary explanations and kin selection (Priority: 3/5): Paul Vasey presents the kin selection hypothesis and evidence from Samoa and Oaxaca, while noting it does not hold up in many Western samples. Cultural stigma and lived experience (Priority: 4/5): The episode incorporates listener testimony from Sudan, Myanmar, and other contexts to show how stigma shapes questions about sexuality and the search for explanations.

Key Arguments: Sexual orientation is unlikely to be caused by one gene; it probably reflects many genes with small effects. Twin data suggest a heritable component: if an identical twin is gay, the other twin is more likely to be gay than the general population. Identical twins can differ because development itself introduces variation, so heredity is probabilistic rather than deterministic. The fraternal birth order effect is robust: gay men tend to have more older brothers, suggesting a prenatal biological influence. A maternal immune response to male fetuses may alter later sexual orientation, though the exact mechanism remains uncertain. Prenatal hormone exposure may shape sexuality; indirect proxies like digit ratios are used because direct measurement is difficult. Parent-child relationships do not determine sexual orientation, even though upbringing affects many other aspects of personality and relationships. Evolutionary kin selection may help explain persistence of homosexuality in some cultures, but the evidence is inconsistent across populations. Social shame and illegality make sexuality research harder, because people may not disclose information honestly.

Data Points: Countries where same-sex sexual activity is illegal: 69 - CrowdScience notes its audience spans countries where homosexuality is criminalized. Estimated number of non-heterosexual humans: 385 million - Used to underscore the scale and significance of sexual orientation globally. Baseline population rate of homosexual orientation: about 5% - Kevin Mitchell uses this as a rough population estimate in explaining twin-study comparisons. Identical twin concordance for gay men: 25%-30% - Mitchell cites higher likelihood among male identical twins when one twin is gay. Identical twin concordance for lesbian women: about 20% - Mitchell gives a lower but elevated likelihood for female identical twins. Older brothers effect: more older brothers than straight men - Dr. Skorska explains the fraternal birth order effect in gay men. Listener’s birth order example: 7 older brothers - Referenced later in the summary as a case where probability of being gay becomes much more likely. Digit ratio proxy: 4th finger longer than 2nd finger - Presented as a possible marker of higher prenatal testosterone exposure.

Pivotal Quotes: "Your genes don't determine your sexuality. Instead, they give you a probability of developing different sexualities, like a rigged die." — Narrator/host: Explaining the episode’s central model of genetic influence. "No, it just can't." — Lisa Diamond: A strong rejection of the claim that parenting causes sexual orientation. "There is only one thing that humans are born, and that is changing." — Lisa Diamond: Describing humans as developmentally immature and emphasizing ongoing development.

Implications: The episode reframes sexuality as a complex developmental outcome, reducing blame on families and highlighting biology, prenatal factors, and stigma. It suggests future research must look beyond simplistic cause-and-effect explanations.