That's mathematically impossible. If you took the first 10 males and 10 females on Earth, and half of them possessed a "gay" gene where they were born homosexual; The 5 straight couples would engage in opposite sex relationships, procreate and thereby propagating their bloodline to continue through time. The 5 males and 5 females that possessed the "gay gene" would engage in same sex relationships, then they would grow old and die off. They would just be a memory to the ether.
So even if such a gene existed in the first tribes, it would cease by the end of the individual's lifespan. So there would be no possible way to pass on such a gene throughout history.
Homosexuality is a choice. Anyone who believes otherwise is just a brainwashed low IQ puppet. And I could care less if a person is gay or not. Just stop spreading these lies and propaganda because you're insecure about the choices you made in life.