While there is very little evidence of homosexual orientation on my mother's side of the family, there is plenty of it on my father's side of the family. Dad's father had a brother who was homosexual in his sexual orientation. Dad was exclusively heterosexual. But, I also think that one of his brothers was a homosexual who was heterosexually married. That Uncle never had any children, just like his and Dad's uncle didn't.
Dad's other brother has a son who, for all intent and purpose, to borrow a phrase, is a bisexual. I know that because my older brother, although he later married a woman, had lots of sexual activity with that particular cousin during their teen and early adult years. My older brother even shared the same bed with him when he lived with them for a while.
My older brother did get married; but, he never dated a girl nor woman until after he was 23 years old and was tricked into that marriage. He did have 3 sons and the older son was homosexually active all during his teen years. I really think that the next younger son is more homosexual than heterosexual and that is based on how he talked AND acted when I was around him.
One of Dad's sisters had a grand-daughter who liked women more than she did men, according to what my mother told me after talking to his sister one time.
A PhD psychologist here in Tulsa, Oklahoma, at the Indian Health Care Resource Center's Behavioral Health department, told me that he believes that more than one gene is involved in what decides one's sexual orientation. I tend to agree with him.
I dated women while in high school and in adult life until I was past 35 years of age; but, while I loved as a friend the women I dated, I NEVER experienced a physiological sexual attraction directed toward them. That means we would never have been sexually compatible. For a male human being, he always experiences a physiological sexual attraction down-below-the-waist, behind-the-pubic-bone, in-the-area-of-the-prostate-organ, directed toward those nearby according to his sexual orientation.
He does not even have to be thinking about sex with the person nor even be looking at the person to experience a physiological sexual attraction directed toward that specific person. Blind persons experience them.
