Selfish Reasons to Have More Kids: Why Being a Great Parent is Less Work and More Fun Than You Think

by Bryan Caplan

Parents may have a small effect on sexual orientation. Psychologists used to label homosexuality a mental illness caused by overprotective mothers and distant fathers. Now we tend to see sexual orientation as a preference inherent in our genes. When you look at the evidence, 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. Yet genes are far from the whole story—if you’re gay, your identical twin is usually still straight. Upbringing might make a difference, too. In surveys, adopted brothers of gay men and adopted sisters of gay women are about six times as likely to be gay as the general population. This would normally be a smoking gun, but sexual orientation remains a touchy issue. The adoption results might merely show that gays with gay adopted siblings were six times as likely to mail in their surveys. A large Swedish twin study with an exceptionally high response rate—nearly 60 percent—confirms a small nurture effect for women’s orientation, but none for men’s.

Changing mores and base rates of professing homosexuality probably matters a ton here