My question is how do they separate the nature from the nurture in this scenario. Two brothers may have the same genetice code, but they also share the same environmental forces that might steer them towards homosexuality.
Yeah, a better test (to the extent there is ANY validity here, which is a big question) might be to test gay and straight brothers.
I actually know of a family of 9 brothers, 2 of whom ended up gay. One of the two is dead of HIV, though.
Messed up home life, though. Mother was a real domineering witch. Father very weak.
See my post #14. The "researchers" separate nature from nurture at the outset. They will study physical characteristics that are most likely the results of a behavior (they skew the study in this direction by only sampling self declared adult homosexuals) and then they will attempt to claim physical results (a linkage) to an as yet unidentified innate "orientation"...
"... how do they separate the nature from the nurture ...
The only meaningful experimental design for this question is to study a random sample of identical twins who were raised in separate families.
Homosexuality is not a condition, it is a means of expression; it's fun, exciting, dangerous and gets you noticed, what's not to like?