David Farrar: Homosexuality linked to older siblings

Until recent years there has been no real idea why 5% or so of the population are attracted to their own sex, rather than the opposite sex. It clearly isn’t a choice, but what was unknown is whether it has a genetic link, or an environmental link or both – and how much.

I have blogged previously on how some studies have shown that there is a link to having older brothers. A new study of nine million people in the Netherlands has been of much higher quality than previous studies, and confirms them. They note: