There's supposedly some neurological studies out there about the origins of transness, but they're not very good:

Neurology should in principle be able to completely settle what causes transness. But what are the commonly proposed causes? Here's two theories that I've seen discussed a lot:

Beyond these two, I also want to introduce three other theories that can be considered plausible:

If a good neurological study is performed that proves one of these theories, then the market will resolve to the corresponding theory. If a 

 good genetic study or other study proves one of these theories, and people stop investigating it neurologically for some reason, then the market will resolve to the corresponding theory. If no theory gets proven then the market doesn't resolve. If it becomes unresolvable (e.g. all of humanity gets uploaded to computers through some means that doesn't preserve information about how transsexuality works) then the market resolves N/A.

If repression or social contagion (ROGD) plays a role, then repression or social contagion will not be counted, and we will instead consider the other factors residual for repression or social contagion.