In a graduate psych text in the 70's I learned that autopsys showed that a small proportion of gay males have rudimentary structures similar to female sexual organs with bone structures similarly feminine. This tells me that there is a genetic component to some percentage of homosexual orientation. But not all.
As some one else said, there is a spectrum of genetic and leaned behavior. I often wonder if the current homosexual campaign is designed to push the margin, and increase the homosexual numbers?
You'd do well to ask Scripter and/or EdReform about that text. It was likely a fabrication by pro-homosexual text book writers or faux researchers. I have never, ever heard or read that, and if it was really true, it would be blasted all over the place, since homosexual pushers are searching devotedly for anything that proves their points.