Even though we primarily have two genders - male and female, this is not an absolute measurement of one's gender identity. Even though physically we might be able to categorize into 2, 3 or 10 genders (based on organs and physical features), the composition of brain and the body as a whole (inside and outside) can only define one's gender precisely. So to say no one is born gay, lesbian is to say no one is born straight too.