The brain is a biological organ. Sometimes people’s brains don’t match up with their external genitalia. Their chromosomes might or might not correspond with one or the other. Transgender identity is to all indications a natural biological variation.Biology determines who is male and who is female. The other way is mental illness. You may well be afflicted lifelong with the mental illness and it is worthy of compassion but not indulgence. You don't indulge mental illness. It makes it worse and may even promulgate it so that the affliction spreads to others.