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).
But bear this in mind, parents, there are other ways for your child to contribute to your overall genetic success than humdrum sexual reproduction. I don't know how much money or residual fame is trickling down to, say, k. d. lang, Elton John and Rachel Maddow's close relatives, but I can only imagine that these straight kin are far better off in terms of their own reproductive opportunities than they would be without a homosexual dangling so magnificently on their family trees. So cultivate your little prehomosexual's native talents, and your ultimate genetic payoff could, strangely enough, be even larger with one very special gay child than it would be if 10 mediocre straight offspring leaped from your loins.
If researchers eventually perfect the forecasting of adult sexual orientation in children, would parents want to know? I can say as a once prehomosexual pipsqueak that some preparation on the part of others would have made it easier on me, rather than constantly fearing rejection or worrying about some careless slipup leading to my “exposure.” It would have at least avoided all those awkward, incessant questions during my teenage years about why I wasn't dating a nice pretty girl (or questions from the nice pretty girl about why I was dating her and rejecting her advances).
And another thing: it must be pretty hard to look into your prehomosexual toddler's limpid eyes, brush away the cookie crumbs from her cheek and toss her out on the streets for being gay.