Cross-cultural data show that prehomosexual boys are more attracted to solitary sports such as swimming, cycling and tennis than they are to rougher contact sports such as football and soccer; they are also less likely to be childhood bullies. In any event, I distinctly recall being with the girls on the monkey bars during recess in second grade while the boys were in the field playing football and looking over at them, thinking to myself how that was rather strange. I wondered why anyone would want to act that way.
Researchers readily concede that there are quite likely multiple—and no doubt extremely complicated—developmental routes to adult homosexuality. Heritable, biological factors interact with environmental experiences to produce sexual orientation. Because the data often reveal very early emerging traits in prehomosexuals, children who show pronounced sex-atypical behaviors may have more of a genetic loading to their homosexuality, whereas gay adults who were sex-typical as children might trace their homosexuality more directly to particular childhood experiences.
Then we arrive at the most important question of all. Why do parents worry so much about whether their child may or may not be gay? All else being equal, I suspect we would be hard-pressed to find parents who would actually prefer their offspring to be homosexual. Evolutionarily, parental homophobia is a no-brainer: gay sons and lesbian daughters are not likely to reproduce (unless they get creative).