To me, it seems that nearly everyone is
to an extent bisexual. To an extent, the majority are attracted to the opposite sex while still have a small sexual appeal towards the same. If you look at every past civilization of humans, the majority of people were actually bisexual or even homosexual. The only difference this time is, our society has evolved to imprint in our minds that it is taboo to be bisexual or homosexual, so we consciously ignore any homosexual attractions. Also, look at
the majority of mammalia. Anyone who has ever raised two same sex animals would see this. My three dogs have go at it every day. That's beside the point that most mammals usually are bisexual. We just put taboos on it, for no real reason.
Homosexual behaviour is known in at least 450 different animal species.
The most homosexual animal appears to be the giraffe. More than 90 per cent of all giraffe sexual encounters are of males mounting other males and, appropriately, male giraffes will "neck" their fellows, winding their necks around each other in foreplay. At any time, up to two per cent of the male giraffes on the planet may be necking others.
Male walruses are almost as homosexual. At any time, up to one per cent of the male walruses on the planet may be engaged in homosexuality in the water, and only during the mating seasons will they turn to the females.
Homosexuality is also found in birds. Swans and flamingos can be exclusively gay, and individuals of either sex will bond for life with others of the same sex.
Hedgehogs are often lesbian. Some 10 per cent of long-eared female hedgehogs will engage in sex with other females, and their practices, which include oral sex, can be surprisingly sophisticated.
It's obviously not a choice if it happens in animals that cant make such complex decisions. Let alone most cant choose which way to go based on memory, like dogs do.