Today, we will be asking ourselves a rather intricate question: what exactly is a Gem? Instead of asking a question of what they are generally, we are going to start more specifically, and do a quick biological rundown on what a gem is!
As a quick answer, Gems are an extraterrestrial species of "magical" beings that are central to Steven Universe. But of course, I deplore the quick answer! Let's get into the nitty-gritty.
Gems are immortal extraterrestrials with a crystalline gem that are all based in Earth variants of gem (pearls, rose quartz, amethysts, diamonds, etc). The type of gemstone that they were grown from (usually) determines their general stature and bodily shape, as well as their powers (which I'll get into in a second).
The gemstone itself is the only part of a gem's body that is actual matter. Everything about who the gem is - what you could call their soul - is within the gem. This makes the gemstone itself a sort of naturally occurring computer. How these computers work or form is yet to be fully explored in the show, and is left to fans to theorize about for the moment. At least to me, these gemstones that are attached to their body-manifestations are the most interesting part of Gem biology!
Now, a Gem's detailed form is left to the discretion of the particular gem. They have a fair degree of control over the shape of their body, although it requires mental effort and concentration to change from the "default" form they have. They reproduce artificially by planting seeds that grow into new gems in the crust of certain planets (like Earth), and their offspring are more or less genetic clones of their parents. If a Gem's body is sufficiently injured, the projection of its form and the gems will enter a state of stasis where they will eventually regenerate a new body.
Gem reproduction is also really unique! Gems reproduce artificially by planting seeds that grow into new gems in the crust of certain planets (like Earth), and their offspring are more or less genetic clones of their parents. Sometimes, though, a Gem's incubation process can be interrupted, resulting in an "unfinished" Gem, as Amethyst of the Crystal Gems is.
Some of the aspects of their biology are a mystery even to the Gems themselves, and some of these abilities are taboos or sources of deep cultural conflict. Their subspecies are divided into castes. Each caste has one or more powers which are indistinguishable from magic, including telekinesis, pyrokinesis, precognition, etc. They can fuse together to increase their strength and abilities, although in their mainstream culture this is only permitted among the same caste.
On top of this there bodies are biologically well-adapted to space travel. They're comfortable in vacuum, their bodies adjust to any level of gravity, they don't have to eat, and they can apparently make more Gems using only inanimate rock.
Compare to humans, who need an oxygen atmosphere in a narrow range of temperatures and pressures, a balanced diet of nutrients which are mostly only available on Earth, and who get muscular degeneration just from being in zero gravity for too long.
The most interesting thing about the Gems on a biological level are the gemstones that are attached to their bodies.
But of course all of this could change with the release of the new season! So if that happens this was a complete waste of time. And if that’s the case have a great day!