But it's not strong from a statistical point of view. These people share the same genes, so if it were genetic it should be very close to 100%. Either:
1) It's environmental
2) It's a behavior, which 50% of the people w/ this 'gene' are able to control.
3) Fraternal twins are irrelevant. They are like all other siblings. So 20% share it; well, close to 100% of fraternal siblings share the same upbringing.
Option 2 is the answer. It's a mix of environment and genetics (according to this article).
To add to my previous post...
Also if you read the article it says there are people with the gene that aren't "gay". If anything I think this gene is a gene that makes one attracted to the opposite sex. But acting on it, is environment.
Just like there's probably a pedophile and serial killer gene, society prevents many from acting on it by strong punishment for such actions. Gay lifestyle is being praised in the West, so more and more people with the gene will act on their nature. Which I think is bad for society as it breaks down family and takes us one step closer to legalizing pedophilia.