The biology of sexual orientations has intrigued people for generations. Many models have been providing insights to that topic, but there are still unanswered questions. In humans, sexual orientation has a learned component. Humans have to learn cues by which they identify the sex of their mates, and cues of the emotional messages that those mates broadcast. Many of those cues depend on arbitrary societal conventions. The cues are learned automatically and subconsciously during childhood, based on non-sexual experiences. When sexual orientation emerges at puberty, the youngsters cannot tell how and when they have acquired it. A model that deals with those phenomena is presented. A basic tenet of the model is that a sexual orientation is determined by the innate wirings of the brain. The model describes how the brain learns cues for identifying the sex of the mate, and cues for identifying emotional messages that the mate broadcasts. The learning mechanism is conditioning. The unconditioned stimulus is human voice. The unconditioned responses are the triggers of the physical and emotional manifestations of sexual activity. The model suggests that innate connections from auditory detectors of men’s and women’s voice onto brain centers that trigger sexual activities, such as the hypothalamus, determine the sexual orientation that emerges at puberty. Innate connections from those auditory centers to emotional centers, such as the amygdala, determine the learned emotional cues. It is also proposed that during evolution, the roles of the chemosensory system in identifying mates were taken over by the auditory system.