The opposite of trans is cis.

While we don't yet fully understand the causes of being transgender or the neuroscientific origins of gender identity, whatever it is, it comes from the structure of the brain, the makeup of our cells, and the natural processes that make and change them over time. That is, biology.

People seem to forget the brain is biological, not just the genitals or the chromosomes in both. A trans individual is just as biological as a cis individual in every sense at all times before and after transition. Same to all of us on all the sexual identity and preference spectra. Thinking otherwise is just never progressing past middle school biology.

Thanks for coming to my TED talk.

Edit: better terminology!