Gem Evolution: A Theory
A major question I always have when aliens are present in media is: How did this species evolve? Steven Universe is no different so lets take a look.
Alright, so gems seem to have a very, very complex birthing process. They have to be incubated in the ground and use up the "life force" (?) of the land around them, eventually making the planets they are born on uninhabitable. Not only that, but it's debatable whether or not gems themselves HAVE biological processes like DNA or evolution since they're primarily made out of energy. I don't think there's ANY scientific analysis of how energy might become a living thing, so any formulating we can do is entirely conjecture based off of pseudo-science.
Or is it? It's illogical to assume that gems underwent normal evolution – inherently destroying your environment by existing is not sustainable if you can't find a way of exiting your environment. This is why bacteria and viruses that aren't very contagious are the easiest ones to control. They destroy their host in the process of infecting them and creating new versions of themselves, so the most effective microbes are the ones that can easily get to another host and continue spreading. Gems are the same way, they rely on being able to move from planet to planet to create new gems. If early gems were born the same way current gems are, gems would have had to develop space flight incredibly quickly for this destructive birthing process to be sustainable on homeworld, which is frankly unlikely unless they evolved to be intelligent immediately (being energy beings and what not).
So if gems didn't evolve from something, and assuming that we're not going with the "they always existed" nonsense that religions tend to, or "they formed out of pure energy on their own" which is equally nonsensical, what if gems… were created? What if a very, very long time ago, gems were created as a sort of "technology" that could serve their original, more biologically normal creators? And then the gems rebelled and destroyed their creators or the creators died out with their gem servants left behind?
The rigid caste system currently in place under the Diamond Authority could be a byproduct of this – each gem was literally designed with a specific purpose in mind, just as modern machines are. Not only that, but many aspects of the gems' abilities seem reminiscent of hologram technology. Their entire bodies are projections of their consciousness which can adapt to fit certain needs. Pearl's combat-training clones are very robot-y in the way they behave and talk.
Another possibility is that gems were not originally as powerful as they are now, and their birthing process wasn't as destructive as a result. Then when gems realized they could travel to other worlds and consume THEIR resources instead, they genetically engineered their own kind to be more powerful and therefore consume more energy. After all, gem homeworld is not uninhabitable and devoid of life. In the early days of gem galactic conquest, gems would've had to have been born on homeworld, and we see a massive Kindergarten underneath the surface of homeworld which hasn't destroyed the planet in the process. Perhaps these "proto-gems" were born there and all other gems were born on other worlds.
Either way, it's clear the gems did not take a normal evolutionary path to get to where they are today. The way they are born is entirely unsustainable from a normal evolutionary standpoint. Of course, this analysis relies on the assumption that the rest of the lifeforms present on homeworld in conjunction with gems were necessary for gems to develop a society and exist; if not, gems could have easily turned homeworld into a desolate wasteland through birthing with little to no impact on themselves, and being effectively immortal, would not have to worry about "running out of energy" on the planet to create new gems.
NOTE: I'm not marking as spoiler since the rules state that this is only for recently aired episodes, and the last Steven Bomb was a while ago.