I started to get into the show just recently, but Gems as a species don't seem to be capable of being created by completely natural and random events as our form of life was. The Gems need to be manufactured in order to make more of themselves, they may have concepts of romantic relationships among other 'high level' feelings, but procreation isn't one of the end results and I can't find a good explanation (yeah there is the example of Steven, but I have a theory that he isn't necessary part-Gem) as to why they would have those feelings if creating offsping didn't lead them to uniting in those strong bonds, so what are they for?
I feel one of two possibilities could have lead to them: 1.) They are the result of a "Post-Singularity" species. That is a species that was once fully organic or something similar to this concept, but eventually made themselves part-robotic then eventually reached a point that they stopped being 'organic'. 2.) The "Terminator" scenario. Robotic beings that killed their creators long ago. This could explain their war-like nature and disliking of other species that were 'naturally born'.