It exists among all species of mammals. That you don't believe it is hardly surprising. You don't believe anything, however true, that goes against your dogma.It doesn't exist anywhere else in the animal kingdom (don't believe the homosexual lobby's propaganda). It is simply a product of the unique human characteristic of Free Will and the Knowledge of Good and Evil. Humans have the freedom to choose lives of carnal dissolution.
That you don't believe it also changes nothing and neither adds to nor detracts from the facts.