If sexual orientation is genetically determined, then the concordance rate among identical twins should be 100%. If one twin is gay, so should be the other. Alas, the concordance rate, according to researchers Peter Bearman from Columbia and Hannah Bruckner from Yale, is somewhere between 5% and 7%. Oops.Nuff said. - See more at: here.The Guardian swallows hard, but notes this fact:
"The flawed thinking behind a genetic test for sexual orientation is clear from studies of twins, which show that the identical twin of a gay man, who carries an exact replica of his brother's DNA, is more likely to be straight than gay. That means even a perfect genetic test that picked up every gene linked to sexual orientation would still be less effective than flipping a coin."In other words, the genetic evidence for biological causation is so poor you'd have better luck predicting orientation by throwing darts blindfolded.
You don’t have to convince me.