I recommend checking out Robert Sopolsky’s lecture series on Human Behavioral Biology. In particular, the 15th lecture on human sexual behavior is where he talks about non-reproductive sex. Here is the video for the 15th lecture:

Well, first of all, being homosexual doesn't rule out fathering children. For men who are 'exclusively homosexual' -- never have heterosexual partners -- children are out of the question. But many homosexuals are not exclusive. A substantial portion of men who have primarily homosexual relationships also have heterosexual relationships, and father children. This complicates life in ever so many annoying ways, but that's just the way it is.

We don't know exactly what determines sexual orientation. It may be determined by factors present in utero which have the consequence of feminizing the otherwise male brain at just the right moment. The male so affected is altogether male, is quite likely to act like most other males, BUT notably, is more likely to prefer other men for sex. Genes may have such an indirect role to play in sexual orientation that we can not now factor them.

Animals and plants have large genomes and even though we have "mapped the human genome" we by no means know what all of the genes do, or what combination of genes and gene switches is required in any instance. So, inheritance of traits (like homosexuality, permissive attitudes, risk tolerance, etc.) is by no means cut and dried.

Sexual behavior in a population plays itself out as a spectrum ranging from exclusive heterosexuality to exclusive homosexuality. The number of men who are exclusively homosexual is a small percentage of the population -- 2% to 3%. When you see figures of 10% of males being homosexual, we're not counting exclusively gay men.

As someone said, the only unnatural sex act is an impossible sex act. People like sex, and whatever happens to arouse them at the moment can lead to sex. That's why many men who are not homosexual have sex with another man sometimes. At the moment it was an arousing possibility. Same thing for more or less gay men. Sex with a woman may, at the moment, be arousing.

Thanks for the info. I will check it out

I recall something from somewhere: Since all fetuses begin as female, the intended-for-male instructions for masculinizing the brain and the body can malfunction, either wholly or partially, and you can work out that this can lead to lesbian, gay, bisexual, and hermaphrodite.

As someone said, the only unnatural sex act is an impossible sex act. People like sex, and whatever happens to arouse them at the moment can lead to sex. — Bitter Crank

True, but: Birds like the Bowebird do all they do to attract a mate. The lyre bird does all it does to attract a mate. The animal kingdom is full of examples of how genetics drive the courtship practice for the end goal of procreation. Then, here we are. I am saying all of this before watching the provided video, or any further research into this topic. I say that because I may be coming from a place of continued ignorance, hence my questions may be answered and I just do not know it yet. If genetics is driven by evolution & natural selection, it would seem that attraction & arrousal in humans would be as it is in the animal kingdom, unless there is another factor in us that allows us to choose against our genetics. Thanks for the response.

Please bear in mind that men and women are not different species, and gay and straight people are not different species. Homosexuality is, as I said, generally not a 100% deal. People aren't homosexual (or heterosexual) 100% of the time. So there is no genetic problem with gay guys having sex with each other.

Homosexuality occurs in other species besides humans. Wild geese are known to form homosexual pair bonds, and go through the ritual of mating. They build a nest, and -- this is most remarkable -- sometimes steal eggs from other nests. The two guys sit on the eggs and hatch them. Male/male bonded geese tend to have high status because males have more status than females, and two males have twice as much. (See Conrad Lorenz: The Year of the Greylag Geese)