Humans are a relatively simplistic species, with very few unique traits or abilities. They have simple needs and originate from the planet Earth. There are two classifications of human: Earthling and Centaurian.
Earthlings are the humans that live on Earth, most of which are unaware of the Alpha Centauri solar system. They very rarely leave Earth and their technology is limited by the GEA, so they have a shorter life span than other humans of about 80-100 years. It is possible for an Earthling to become a Centaurian; they must only travel to the AC solar system and live there.
Centaurians are the humans that live in the AC solar system. There are many of them spread out across the planets, living their lives as others do. With access to greater technology and medicine, the lifespan of a Centaurian is double that of an Earthling. However, it must be made clear that they are the same species; the different classifications are for identifying where they are from and how long their lifespan is.
Pshycolorians began as some of the first Earthlings to enter the AC solar system. Prisoners were sent from Earth to Pshycoloria in an attempt to free Earth of criminals who could not regoin society. Unfortunately, this did not go to plan and the prisoners took over the colony on the planet. Within a few hundred years they had adapted and evolved to live on the planet, and they are now considered a separate species from humans.