Humans are also animals/ mammals, like you rightly said. Humans have the same basic instincts, drives and needs that animals have. The only difference between humans and animals is the more capable 'brain' of the humans. Now, if only humans display heterosexuality, then it is clear that it is because of the human brain. Human brain is known to indulge in manipulating, controlling and destroying nature (outside him as well as inside). This is just another proof that heterosexuality is unnatural. No. Just stating that such basic instincts cut across species and are not limited to mammals. What is the proof that you are not a rare minority? What is the proof that you don't have a natural or a social disorder? What is the proof that it is not becuase of a feminising of your brain, or a rare gene? What is the proof that this is not really a transgender trait, and actually a disqualification for being naturally straight? What is the proof that this is not an anomaly which is being imposed on the straight population because people like you have been given a lot of power on a platter basically by the religion?