To be honest their origins are pretty much what I stated, they naturally evolved, some colonists landed on their planet, the Natvyr adapted their tech as their own and started to spread out.  Not in any uniform way, more than various groups went to colonize other worlds and each other.  Intaspecies history is really repetitive and the only major changes come with adopting tech, which leads to larger hives or filthy clannists.  It's basically a pattern of stable regimes under long lived queens with times of troubles whenever food runs out or too many queens die at once.  Often both.  The ancient colonists being more a group of [insert player made species here] going way out of the way without any contact to others.