- "We built you in our own image, we built you to survive."
- ―Minerva's projection, 1499.[src]
Humans are a species of bipedal mammals that originated on Earth and are, currently, the dominant form of life on the planet. An evolutionary development brought about by the Isu in order to create a numerous, hardy and docile workforce, humans were the result of a forced evolution. Indeed, using a pre-existing primate species, the precursors created the Homo genus according to their needs, via dividing the genus into sub-species such as Homo neanderthalensis to serve as a military force or Homo sapiens to be workers.
Following a prolonged period of peace between humanity and their "gods", humanity rebelled and war broke out. This was followed by a global catastrophe which saw the two species brought to the edge of extinction, wherein they were forced to work together in a much more equal manner than before. Within 100 years of the catastrophe, humanity's creators became extinct, only leaving ruins and scattered artifacts in addition to some of their genes into humanity's gene pool. Now orphans of their creators, the Homo sapiens sub-species assimilated some of the other Homo species, continued to thrive and eventually spread across the globe.
Humanity, including many species of the Homo genus, such as H. sapiens or H. neanderthalensis, was artificially created by the Isu at some point between 1923 and 2296 Isu Era (c.75,383 - 75,010 BCE) to serve as docile servants, workers or soldiers, who saw their creators as gods. However, as time progressed, humanity eventually came to resent the rule of their "gods", and the period of peace that had existed between master and servant gave way to times of war.
Triggered by the theft of an Apple of Eden by the Human-Isu hybrids Adam and Eve, the war blinded both humanity and the Isu to the goings-on beyond their planet, and as such neither race foresaw the pending catastrophe, a solar flare, that would nearly destroy both races, until it was too late.
Brought to the brink of extinction, humanity and their "gods" came together to rebuild. Together, both species built at least three Vaults beneath what would later become the city of Rome, to serve as a warning to humanity's descendants; unlike their "gods", whose small population was approaching complete extinction, humanity's sheer weight of numbers ensured their survival.
As the years passed, the Isu inevitably became extinct, though humankind continued to revere them as gods in their various religions. It was not until the rise of three monotheistic religions of Judaism, Christianity, and Islam, which soon spread across the globe, that humanity began to forget their "gods", though there were those who continued to worship them, and those who came to see the Isu for what they really were. Foremost among these groups were the Templars and the Assassins.
By the 12th century, both Orders firmly believed that the gods of old did not truly exist, and realized that many so-called "miracles" attributed to them had actually been the workings of the Pieces of Eden. However, upon the acquisition of one such Piece – an Apple of Eden – by the Assassin Altaïr Ibn-La'Ahad in 1191, humanity at last became aware of the true nature of the humanity's pagan gods.
Inside, Minerva warned Ezio of the catastrophe her species had suffered, and that it would happen to humanity once again. However, even this did not ensure humanity's knowledge of the true nature of the gods of old, and by the early 21st century, the Assassins once again knew very little of the true nature of the Isu.
However, this changed in 2012, when the Assassin Desmond Miles used the Animus, a device derived from the Isu technology, to relive the genetic memories of his ancestor Ezio Auditore, and witnessed the warning of the future cataclysmic event.
- "We did not build them to be wise. And now they are our final, faulted hope. You are they. You possess the potential for understanding [...] A hundred years I might speak and still you would not know us. You with five senses. Us with six. The one we kept from you."
- ―Juno on humanity.[src]
The human race was developed in the image of their creators, to serve as a docile workforce for the low numbered, but technologically advanced Isu. Artificially developed by drastically altering the pre-existing genetic make-up of native species, the creation of humanity left a sizable gap in terms of transitional species between archaic hominids and modern humans.
By 1997, the Templars, who were aware of the full and true nature of the Isu, had taken note of this, and arranged for fake skeletons to be planted in Ethiopia, so as to limit human exposure to the possibility of the existence of the Isu.
Early humans could not comprehend the true nature of their creators, choosing to see them as gods, and in order to ensure the obedience of their creations, the Isu bred a neurotransmitter into humanity, located deep within the brain. This neurotransmitter forced humanity to abide by the Pieces of Eden, which were technologically advanced pieces of equipment that granted a myriad of powers, including the ability to induce hallucinations in the minds of those bearing the transmitter, as well as telepathically control said humans.
However, there were humans born without the neurotransmitter, and as such were not susceptible to the mind-controlling powers of the Pieces of Eden. Over three centuries, their numbers grew, until they numbered enough to confront the Isu directly, resulting in the war which nearly destroyed both races.
Since some human individuals were born without a neurotransmitter, Clay Kaczmarek would later theorize that this was made possible by cross-breeding between humanity and their "gods", and that not only did this remove the neurotransmitter, or at least the neurotransmitters susceptibility to the Pieces of Eden, but also granted a number of genetically encoded abilities.
One such ability, known as Eagle Vision, was particularly prevalent in the bloodline of the Assassin Altaïr Ibn-La'Ahad, with many of his descendants also bearing the ability.
It was also prevalent in the bloodline of the Auditore family and Giovanni Borgia. Additionally, possession of the mixed bloodline granted the bearer proper control over the technologies of the Isu. Such individuals did not lose their sanity, upon viewing The Pieces of Eden. Ezio Auditore was able to use the a Staff and Apple of Eden conjunction to open the Vatican Vault, whilst the pure-blooded human Rodrigo Borgia could not.