Though they suddenly reappeared in late 2014, it was just that: a sudden reappearance. They existed well before that time but were only in hiding as to avoid any human hunters from killing them off. After centuries of hiding, and being "fed up" with having to remain a secret, they decided to band together and show themselves to the world in the hopes of being able to fit in with human society -- most creatures remained neutral to show their peaceful intentions. This goes without saying that a good handful didn't agree with this kind of thinking. Instead, they sought to "reclaim" their lands since in their mind the world originally belonged to them. Therefore, the mythological population had managed to split themselves into three different categories, those are the same categories the humans had decided to use to determine where each creature stood: Passive, Passive-Agressive, and Aggressive.
How the types are determined has been discussed on its own page, but how they truly came about will be discussed here. Though scientists still cannot explain why the color of their DNA strands has changed to fit their ideologies, they can determine who is willing to cooperate with the human laws set in place and who is not due to that change as well.
Passive (Blue): Those who are considered Passive have chosen to obediently follow along with all the rules and laws set in place by the human race so they may finally be able to live their lives to the fullest rather than have to live in hiding anymore.
Passive-Aggressive (Purple): Those who are considered Passive-Aggressive have chosen to follow along with some of the rules and laws set in place by the human race, though with reluctance. This hesitation stems from their fear of giving up their freedom to be who they are and live their lives to the fullest by bending to said rules and laws without question. They still want to co-exist but not at the cost of be subjected to blatant segregation.
Aggressive (Red): Those who are considered Aggressive have chosen to ignore the rules and laws set in place by the human race because their ideology leads them to believe that the humans have no right in segregating them from their own home lands and planet. Because the human race is an "artificial" race compared to the entire mythological population, those who are Aggressive turn to violence and anarchy in an attempt to prove their point. As a result of their very existence being a threat to the human race and the rest of the mythological population, they are exterminated as if they were any other pest in the world.
Even within the human race, some people strive to help end the blatant segregation going on with the mythological population by holding numerous riots and parades, anything to get their government's attention for them to do something to help rather than harm the mystical creatures that had risked their existence by reappearing before the world.
As mentioned previously, the mythological population still existed before their big reappearance. This being said, many hybrids between a mytho. and a human have popped up from hiding as well. Meaning that a small percentage of humans were already aware of their existence and chose to aid them in hiding their loved one and child/children from the world.