Born this way, baby

[John V]

Then how can a set of identical twins develop with one gay and one not???

Experience shows that identical twins are rarely completely the same. Until recently, any differences between twins had largely been attributed to environmental influences (otherwise known as "nurture"), but a recent study contradicts that belief.

Geneticist Carl Bruder of the University of Alabama at Birmingham, and his colleagues closely compared the genomes of 19 sets of adult identical twins. In some cases, one twin's DNA differed from the other's at various points on their genomes. At these sites of genetic divergence, one bore a different number of copies of the same gene, a genetic state called copy number variants.

http://www.scientificamerican.com/articl...-identical

If you argue that identical twins are, well, not identical in their DNA, then you lose twin studies as support for a genetic component to homosexuality. Which leaves you with nothing solid at all.