One of the most important aspects of sexual reproduction is sexual desire. Every animal species which engages in sexual reproduction has an overwhelming desire to mate hardwired into its very biology. For most individuals, their brains are constructed in such a manner that this desire is centered on the opposite gender. However, for certain homo sapiens as well as for many members of other species, events (whether genetic or prenatal) conspire to produce a male with a brain structure more typical of a female, or a female with a brain structure more typical of a male. In these individuals, the sexual impulse is tuned towards members of their own gender, rather than the opposite. So instead of engaging in 'normative' sexual behavior with members of the opposite gender, these individuals instead pursue relations with members of their own gender who are similarly inclined.
Problem goes where?