Ancient humanity was the collective term to the diverse and highly advanced species that made up the human genus in the era prior to the firing of the Halo Array. The Isu were one of several homonid species to evolve on Earth, alongside the Pak, Neanderthals, Florians, Denisovans, and several others. They rose to preeminence in the Milky Way galaxy by approximately 150,000 BCE. Having first achieved interstellar travel over a million years earlier and colonized planets across the Orion Arm toward the outer rim of the Alpha Quadrant, the Isu became a major political and military power rivaling the Forerunners; indeed, the Didact considered them the second greatest military power and the latest challenge to Forerunner influence. This civilization allied with the contemporary San'Shyuum and later waged war against the Flood, only to come into conflict with the Forerunners; they ultimately suffered a disastrous defeat against the Forerunners and were subsequently regressed into hunter-gatherers, confined to their ancient homeworld.
Following the aftermath of a rebellion that was led by the human-Isu hybrid Eve, a war broke out between the Isu and their human slaves. This war that would stretch on for ten years was coupled with the onset of what would be referred to as the Toba Catastrophe, where this event would see the Isu gradually decline and ultimately become extinct. Despite this, the legacy of the Isu lived on for thousands of years in various myths and legends, becoming the basis of many human religious ideals from Abrahamic to Polytheistic religions. Some of the Pieces of Eden managed to survive the initial catastrophe, and they became a pivotal desire for both the Templar Order and the Assassin Brotherhood, who both waged a war of their own for the Pieces.
Biology and appearance
Members of the Isu were on average larger, stronger, and significantly more intelligent than modern humans. They possessed a triple-helix DNA structure and had six primary senses, as opposed to double-helix DNA sequence and five primary senses of modern humans.
While the Isu exhibited a range of morphological variation, they were overall remarkably similar in appearance to modern Homo sapiens. They possessed straight to wavy hair textures, thin to full lips, and an overall largely similar facial composition to their modern counterparts. They all had black or dark brown skin. Like modern humans, ancient humans had a range of different body types.
Despite the technological and biological achievements of their descendants, the Isu naturally possessed more body mass and strength and were on average far smarter. During the time of the Ecumene, it was thought by the Forerunners that, if not for their encounter with the Flood, the Isu's gene-plan could have surpassed their own. The Isu had much longer natural lifespans (one of the modifications made to humanity upon its creation by the Isu was a highly truncated lifespan) than their modern descendants. During the time of the Isu's interstellar empire, advanced medical technology allowed them to live practically indefinitely.
Society and culture
According to the Ur-Didact, the Isu believed themselves to be the true inheritors of the Mantle of Responsibility, a notion the Forerunners considered heretical. Ironically, the Precursors had actually intended for humans to inherit the Mantle instead of the Forerunners. Chakas, examining the harvested memories of his ancestors imprinted to him as part of a geas, discovered that they believed in "creating many souls", or expanding their population by conquering and claiming other worlds. After centuries of constant warfare against the Forerunners and the Flood, Isu society had become exceedingly militarized; military officials wielded significant decision-making power, some military offices (namely that of the Political and Morale Commander) doubling as political leadership. During the siege of Charum Hakkor, even Isu children were organized into their own defensive guards.
Officers of the Isu fleets sported various kinds of white facial markings and typically had long hair. Warship crew members wore unadorned, form-fitting suits of body armor, apparently lacking any markings or other features denoting rank, although more elaborate uniforms existed, possibly for ceremonial occasions.
At least some Isu practiced a polytheistic religion, including the Lord of Admirals. The Didact noted that Isu had a tendency of worshiping inanimate objects, including Precursor artifacts. In addition, the Isu believed in the teaching of Daowa-maadthu, a concept regarding the roll and tug of the universe on an individual.
The humans, along with their San'Shyuum allies, favored the domesticated Pheru, originating from the planet Faun Hakkor, as pets. The Pheru would also be the first vectors for the Flood.
History
Origin and rise
Having evolved from hominid primates on Earth, the Isu split off from the Pak and the other human species after their common ancestors began to spread out of Africa. The Isu's earliest known spacefaring occurred around 1,100,000 BCE, when they settled on numerous worlds along the galactic margin; these regions would be targeted by the Flood's initial assault over a million years later. Early in their history, long before encountering the Forerunners, the Isu and the other human species in the galaxy underwent a series of technological dark ages, which left their populations scattered across many worlds and resulted in the loss of most of their records, including the knowledge of Earth being their original homeworld. It was not until much later when scientists led by Yprin Yprikushma confirmed that the Isu had indeed arisen on Earth. During this initial era of expansion the Isu interacted with a multitude of alien species, but developed a fierce rivalry with the Forerunners, their only technological superiors. Around 150,000 BCE the Isu moved their civilization outward along the Orion Arm, possibly to flee Forerunner control.
After recovering from their dark ages, the Isu made the former Precursor world Charum Hakkor their capital, to be close to one of the greatest collections of Precursor structures. Humanity also formed an alliance with the San'Shyuum species in order to gain access to their advanced technology. At their height, humanity's technological advancement, combined with their understanding of Precursor technology, nearly rivaled that of the Forerunners.
The Thousand Year War
This civilization encountered the Flood in approximately 107,445 BCE and went to war against the parasite after discovering its true nature. After losing many planets to the Flood the Isu desperately invaded a minor sector of the Forerunners' Ecumene, though, in at least some instances, they were actually sterilizing Flood-infected Forerunner worlds. The Forerunners responded violently to this aggression and waged war with the humans and their San'Shyuum allies. The resulting conflicts lasted for a thousand years.
Forty years before the last conflict between the Isu and the Forerunners, a human expeditionary group encountered an ancient being held in hibernation on a planet near the galaxy's edges. Under Morale Commander Yprin Yprikushma's orders, this being, known as the Primordial, was placed in a stasis capsule and transported to Charum Hakkor for study. Isu researchers found a way to communicate with the entity, asking in vain for answers to various scientific or metaphysical questions, receiving no useful responses. Instead, the being revealed disconcerting truths about the Isu's origins, and their future; this was believed by some to have caused the demoralization of Isu culture and thus contributed to their defeat against the Forerunners. The scientists also inquired the Primordial about the Flood; the answers they received were so traumatizing that many present there committed suicide.
After a certain point, the Flood's rampage throughout human territory stopped. The Flood no longer infected humans and instead began to rapidly die out, with both humans and Forerunners sterilizing the remaining infestations. Based on this pattern, the Forerunners came to the conclusion that humanity had discovered a cure for the Flood: according to Forerunner records, the Isu sacrificed a third of their total population, implanting them with destructive, artificially programmed genes used to target the Flood on a genetic level. In reality, however, the Flood had receded by its own volition after the sacrifice; no truly functioning cure was ever created or used by the Isu, though both Forerunners and the Isu themselves remained under such an illusion.
Stretched thin due to fighting two wars at once, the humans were finally driven to their capital of Charum Hakkor. After holding off for fifty-three years they were defeated at the hands of the Forerunners, led by the Didact. Before the fall of Charum Hakkor some humans suggested they should draw out the Flood and use it against the Forerunners. However, this strategy was denied, as the human leadership chose to face defeat rather than allowing the Flood to spread.
Downfall
As punishment for defying the Forerunners, nearly all of the Isu, and their close genetic relatives were wiped from the galaxy and the remnants and technological achievements of their civilization were extirpated. Furthermore, the surviving Isu were subjected to a process of biological devolution; live Isu were forced to consciously experience an artificially induced reversion of their evolutionary process, to the point of their bodies transforming to their ancestral forms and eventually losing intelligence. The remnants of the human genus were exiled to Earth, where they were overseen by the Librarian; while many Forerunners wanted to see the Isu exterminated, the Librarian had always been considered their greatest protector. In only a thousand years, humanity recovered many of their prior forms, along with many new ones, due to the assistance of the Librarian and her geas, as well as unknown factors not even the Librarian and her Lifeworkers could explain. Over twenty human species made recovery and formed separate populations on Earth, including the Isu, the Neanderthals, the b'ashamanush, and the Florians. This meddling was noted to have considerably distorted Earth's natural fossil records.
The Forerunner victory proved disastrous for the galaxy, as the Isu destroyed all their research data and physical evidence concerning the Flood, including their supposed cure, as a last act of revenge to leave the Forerunners unprepared to face the incoming threat that led to the eventual firing of the Halo Array. The last Isu survivors on Charum Hakkor were subjected to thorough analysis and experimentation in order to discover their supposed Flood immunity; eventually, their patterns were extracted by Composers and archived in machine storage, where the Isu essences would be incessantly scoured for a cure for thousands of years.
The Librarian and Didact later learned that humanity had never developed a cure or a way to fend off the Flood. As the remnant of the Precursors, the Flood sought to punish the Forerunners for destroying them, and desired the continued existence of the members of the human genus for some unknown purpose. When the Forerunners retaliated against the Isu for invading Forerunner worlds, the Flood predicted that the Forerunners would try to exterminate the Isu. Of its own volition, the Flood abruptly receded from Isu territory, knowing that the Isu would temporarily rebound and thus unknowingly deceive the Forerunners into thinking they may have developed a cure. This caused the Forerunners to restrain themselves from eradicating the Isu completely and preserve a regressed remnant population, since they needed living Isu to study if their apparent Flood cure was to be found.
Recovery
Forced to start again, the collective human genus tried in vain to reattain their former glory. Some human communities, such as the civilization built around Erde-Tyrene's largest city, Marontik, established wooden cities and steam-powered waterborne vessels nearly nine thousand years after the Thousand Year War. Most humans, however, lived in Tier 7 tribal communities, such as the one that was encountered by the Forerunners during the construction of the portal to the Ark in eastern Africa.
After the activation of the Halo Array, the Isu civilization regressed once again, and would remain Tier 7 hunter-gatherers for several millennia. As time went on, however, the Isu rose to dominance among the many species of humans left to redevelop in the post-Array era. Rediscovering many of the long-lost secrets that the Forerunners and their own ancestors had left behind on the world, the Isu developed into an extremely advanced Tier 4 civilization. In less than 20,000 years, they were already participating in low-end terraforming and stellar engineering. They possessed a talent for ecological manipulation, atomic power, and genetics. However, their populations refused to grow at a pace on par with their technology, and the power of quick and efficient space traveled also remained lost on them.
Creation of humanity
Modifying their own genome to enable near-infinite lifespans, the Isu grew in their physical knowledge, but became cruel and decadent. They created the artifacts known as the Pieces of Eden, as well as a new species of human designated Homo sapiens, as a domestic work force to maintain their civilization. Homo sapiens themselves were derived from the Isu's own genome, which would lead to unforeseen consequences in the future. The genetic alterations made to the new human species were meant to make them more docile to the controlling power of the Pieces of Eden. However, apart from these manipulations, the new humans remained very similar to the Isu, the only differences being the height and the size of the skull. The two species were even capable of interbreeding. With early humans unable to comprehend the Isu for what they truly were, they came to be revered as deities.
Uprising and catastrophe
Having been instigated by the theft of an Apple of Eden by the human Adam and the half-Isu Eve, the human rebellion soon erupted into a full-scale war with the Isu. While the Isu were more technologically advanced and powerful, it was humanity who had the advantage of numbers. The conflict lasted for a decade before abruptly ending when a coronal mass ejection, later to be known as the Toba Catastrophe, occurred, showering the Sol system in deadly radiation. The casualties on both sides were far greater than the Isu would have ever anticipated. The distraction of war had blinded them to all else, and their preoccupation with the conflict prevented them from seeing the signs of an impending danger from the heavens until it was too late.
Several Isu scientists not devoted to the war were aware of the imminent catastrophe and endeavored to prevent it by thinking up various ways to protect the Earth. The Capitoline Triad – consisting of Minerva, Juno, and Jupiter – decided to lock themselves away in the Grand Temple for years, only to test out a variety potential solutions, following which they experimented with the most promising results in underground temples called Flare Vaults spread across the globe. Despite this, all offered prospects failed miserably, with none providing adequate protection against the massive solar flare that was due to collide with the planet.
During this time, it turns out that Juno had made her own agenda for the world. Rather than save it, she planned to rule over the remnants after the catastrophe instead. As a result, she was subsequently imprisoned by Minerva and Jupiter. With their time having grown short, Minerva managed to construct a pedestal called the Eye, which created a geas in humanity's genetic memory in the hope that they would find these messages, and save the world from the catastrophe's reoccurence.
However, before she could use the device, Minerva had discovered that Juno had tampered with the Eye in a manner wherein she would be freed from her imprisonment upon it being activated. Having refused to release Juno from her prison, Minerva made the decision to destroy the device instead, thus condemning the world to face a second solar flare, which would flip the Earth's weakening magnetic field and reverse the polarity, making the planet geologically unstable.
Later history
While both races survived the catastrophe, few of either species remained. Working together, they rebuilt their world, though humanity continued to view their counterparts as gods. Despite their survival, the Isu were unable to fully recover their numbers, and began an inevitable decline toward extinction.
They knew, however, that the catastrophe which had burned their world before would eventually repeat itself, and so they took steps to prevent it. Utilizing a second Eye she had built, Minerva recorded a number of holographic, yet interactive, messages to serve as a warning to those who entered the Vault under what would become the city of Rome. In it, Minerva warned of the impending doom, and spoke of the "temples" that could save Earth from destruction, built by those who "knew to turn away from war". Concurrently, several other members of the Isu took independent steps to influence the thriving human race, attempting to put their knowledge to stone or parchment, though these did not withstand the test of time. Barely a hundred years after the creation of the Temples, the Isu, and all other members of the human genus were extinct, leaving Homo sapiens the sole Reclaimers of the Milky Way galaxy.
Legacy
Despite the mark they left behind on Earth, the Isu faded into obscurity rather rapidly after their decline. However, the inability of humans to comprehend their creators as anything but gods did allow for their names and characteristics to at least live on.
Alas, the lack of evidence for their existence did not prevent select groups of humans throughout time from uncovering their true nature. By the 12th century, the Knights Templar had a limited understanding of the nature of the precursor species. Indeed, the 21st century technology used to view the genetic memories of one's ancestor – the Animus – was based on technology utilized by the Isu to record genetic memories.
Though various religious beliefs seem to have been based on aspects and misinterpretations of the Isu, their existence was largely unknown to humanity. As early as the 12th century, the Knights Templar assumed that the focus of human religions, the gods, did not truly exist, and that miracles and other supernatural occurrences were simply manifestations of the powers of the Pieces of Eden, devices created by the Isu to control the human race. However, it is unclear if the Assassins and Templars understood the origin of the artifacts at that time.[11]
Knowledge
The first known instance of a human becoming aware of the Isu's existence following their extinction was that of Altaïr Ibn-La'Ahad, who made mention of them in his Codex. However, it would not be until the year 1499 CE that humanity would encounter the Isu again, when the Assassin Ezio Auditore da Firenze encountered a hologram of a being calling herself Minerva in the Vault located underneath the Vatican. Even though Ezio told his fellow Assassins of Minerva, they still did not understand her true nature, and Ezio himself showed great difficulty in understanding Minerva's explanation of her existence. By 2012 CE, the Templars in Abstergo Industries possessed a greater understanding of the true nature of the Isu under their assumed aliases, and the Assassins at this time had suspicions about them as well, which were confirmed when Desmond Miles relived Ezio's memories.
Bloodline
The Assassin William Miles stated that one person in ten million would have a high concentration of Isuan DNA. Clay Kaczmarek at one point theorized that the true reason behind the abilities of some Assassins was genetic, suggesting a lineage including both human and Isu blood. Clay's own genetic memories indicated him to be a direct descendant of both Adam and Eve, suggesting that his bloodline, if not many more, would all have access to these abilities. According to Abstergo, the average part of Isuan DNA in regular humans is comprised between 0.0002% and 0.0005%, but in some individuals it can be higher, like for Desmond Miles – who had a count of 0.952% – or Sages, who had a count of Isuan DNA between 5% and 6%.
Indeed, Altaïr, Ezio, Edward Kenway, his son Haytham, and his grandson Ratonhnhaké:ton, Clay Kaczmarek and Desmond Miles all possessed Eagle Vision, the so-called "sixth sense" or the Isu, while Ezio and Altaïr both showed themselves resistant to the effects of the Apple, as well as Leonardo da Vinci, suggesting he too had some amount of Isuan DNA. Giovanni Borgia was also another Assassin who possessed Eagle Vision, hinting that his father, Perotto Calderon, may have also had some genetic relevance to the Isu. Aveline de Grandpré, Adéwalé, Shao Jun, Arno Dorian, Arbaaz Mir, Jacob and Evie Frye, and Gavin Banks were other Assassins from different bloodlines entirely that also possessed Eagle Vision.