My take from Selfish Reasons to Have More Kids:


Parents have a small effect on sexual orientation. Psychologists used to label homosexuality a “mental illness” caused by overprotective mothers and distant fathers.[i]  Now we tend to see sexual orientation as a preference inherent in our genes.  When you look at the actual evidence from twin and adoption studies, however, neither story quite works.  Genes definitely play a strong role – every major twin study finds that identical twins are more alike in their sexual orientation than fraternal twins.[ii]  Yet genes are far from the whole story – if you’re gay, your identical twin is usually still straight.  Furthermore, family environment clearly affects sexual orientation.  The smoking gun: Adoptive brothers of gay men and adoptive sisters of gay women are about six times more likely to be gay that you would expect from chance.[iii]  On balance, the evidence that parents make kids gay is a little stronger than evidence that parents make kids well-educated, rich, pious, or chaste.  While heredity is the star of the story, upbringing plays a modest supporting role.

 


[i] Bayer, Ronald.  1981.  Homosexuality and American Psychiatry: The Politics of Diagnosis.  NY: Basic Books.

[ii] “Genetic and Environmental Influences on Sexual Orientation,” in Handbook of Behavior Genetics, p.271.

[iii] “Genetic and Environmental Influences on Sexual Orientation,” in Handbook of Behavior Genetics, p.271.