The Human Race originates from places unknown but during the Desolate Era Immortal Emperor Jiao Heng, the very first Immortal Emperor of the Human Race, lead the humans from across the Nine Worlds where they were weak to the Mortal Emperor World and made it their sanctuary.[?]
After much fighting they finally become the most dominant race of the Mortal Emperor World and due to the large number of humans who gathered in this world, they are weaker in other places in the Nine Worlds and sometimes they are suppressed in these worlds.[?]
The general shape of the human's body with its bones, blood, and muscles is considered as one of the best physical bases to contain life and to accept and store the Spirit Energy. Many other races imitate the form of human body; for example Stone Golems deliberately cultivates their stone bodies into flesh.
If others Races are favored by the heavens, Humans are the thorns in the heavens’ heart. They could adapt to any environment and take root there. If they really wanted to make a world their home, no one would be able to stop them. Furthermore, humans are the race with the strongest reproductive power, capable of giving birth to more offsprings than any other race.
Pure-blooded indiviuals from other races prefer a human partner in order to pass their bloodlines. Normally a pure Human bloodline wouldn't compete aganist an equal pure bloodline of another race, so the non-human bloodline would prevail.