How To Create New Yor Citizens?

You have to research Space Elevators -> Planetology -> Xeno Manufacturing. Once you have Xeno Manufacturing, a new planetary project will appear, "Manufacture Population". It requires 1 promethion and 1 durantium for each Yor manufactured.

It also requires 80 production per new Yor population.

I don't think you should need a tech or resources to build new Yor. It doesn't make sense to me. The Yor should have been able to make new Yor units in the eons they have existed. They shouldn't need new tech. Likewise, the resources needed to build new Yor don't exist on the Yor homeworld. How could have they survived without such resources?

Edit: An idea I have, I think it would make sense for The Yor to start with the ability to produce Yor, but for the process to be a bit different. It would cost more production, but it wouldn't require fancy techs or special resources.

I disagree wholeheartedly.  Carbon species (and I suppose silicon ones, though this is yet to be proven) grow naturally.  It is just a function of their species.  Yor already have Extreme Colonization (which is far better and more interesting than in GC3, so far).  Unbounded ability to grow would make them extremely overpowered.

In playing as Yor in the recent Alpha, the search for Promethium has been a huge impetus in my expansion (Durantum seems to be more common).  This gives me a reason to research travel through the gates.

(edit)  also, the need for the two resources is not all that great.  Survey ships can reward both resources.  Between that and a few constructors (or planetary mines) the resource requirement isn't very limiting. 

How the Yor are pretty easy:

- very low food requirements (only needed for organic citizens)
- colony ships are practically free ( 20 command points every 5 turns )
- extreme colonization from the start (extreme planets have far more bang for the colony ship)

My first actual citizen build out of Iconia is a constructor.  Usually for Durantum, but if I see a Promethium I'm going straight for it.

Thank you for the information about how to create new Yor citizens.  I was able to research the required technologies and start manufacturing new Yor.

Last game I played as Yor I was really lucky and had a promethion stone deposit on Iconia.

I'm playing as human and conquered a few Yor Worlds, but the Manufacture Population project is not available, and I have Xeno Manufacturing technology. What else do I need? I can't find anything related to Yors in the tech tree.

Or is it impossible because I'm human?

As far as I know, you cannot maufacture new Yors, if you are human. Also keep in mind, that if you transport some of those Yors to other worlds, your people are not going to like it.