One of the things that I love about Final Fantasy, is that even thought all the games are separate histories, there are some key elements that appear in most of the games, and that makes it feels like a large interconnected universe.
I was replaying FF4 and came up with a interesting theory I would like to share here.
In FF4 there are two humanoid races in conflict, the humans, native to the blue planet, and the Lunarians native to a unnamed planet that was destroyed under unexplained circumstances, forcing its inhabitants to escape to space, in a giant spaceship shaped like a moon.
The protagonist of FF4 is Cecil Harvey a knight that late in the game discovers that he is half human and half Lunarian, now the fact that these two different species could interbreed and give birth to fertile offspring (Cecil himself has a son with a human woman in the sequel) proves that Humans and Lunarians have very similar DNA, my theory is that Lunarians are the step above humans in the evolutionary ladder.
Lunarians look pretty much identical to humans, the only notable characteristic in the Lunarians that we meet in FF4 and its sequel is the color of their hair (Both Cecil and is brother Theodore / Golbez have silver hair, Fusoya has pure white hair and Cecil's son Ceodore has blue hair) but they also have some special abilities, Lunarians are proficient in the use of magic, also Lunarians seem to have the ability to keep existing in spirit form even after their physical bodies are destroyed, we meet the spirit of Cecil's father Kluya early in FF4, and the final boss of the game is the spirit of an evil Lunarian named Zemus.
Now the Lunarians's plan in FF4 was to wait in their spaceship until humans had evolve to their level, then they could begin a peaceful merger of both species / civilizations, my theory is that by the time of Cecil's adventure the humans of the blue planet had already reached that point of evolution.
My reasons to believe this are:
There are several people in the world with high skill in the use of magic (Tellah, Palom & Porom, Rosa, Rydia) and many others that practice it to a lesser degree.
Some people have demonstrated the skill to keep exiting in spirit form even after death (Anna appears in spirit form to cheer prince Edward and Tellah appears in spirit form to give energy to the heroes in the final battle of the game).
But FF4 also has another humanoid race that appear in the mid point of the adventure, this race is the Dwarves, now from what I learned about these people in the course of the game, I concluded that they are the previous evolutionary step before humans. Dwarves originated in the underworld and thrived using the power of magma, eventually some Dwarves climbed to the surface and founded the first surface town, and eventually evolved to a more human appearance, in fact the FF4 sequel shows that Lucca, the Dwarf princess, looks very human like, the only notable differences is that her skin is a little darker and she is a little short and chubby.
But no all humanoid species were so fortunate, there are several humanoid creatures that became evolutionary "dead ends" and just get treated like "monsters" some examples are the Goblins, Ogres, Trolls, Gorgons and Lamias.
I think this evolutionary line applies to all the Final Fantasy games, just that with different names for the different races due to different cultures, for example in FF1 there is an ancient technologically advance race that invented the Airships, and in their town, they have the most powerful magic spells in the whole game, they are called the "Lufenian", and are very similar to the Lunarians of FF4, in FF7 the ancient, wise, magically gifted people of which Aerith descends are called the "Cetra", but functionally they are very similar to the Lunarians of FF4, just to name a couple.
I think this a very cool detail, and one of the core elements of a shared Final Fantasy Universe.