Humans - Restoration of Humanity: By the time of the Unification Wars that established the Emperor of Mankind's rule over Terra, the Human homeworld's population had suffered through the horrors of the Age of Strife, a period punctuated by constant warfare and the use of weapons of mass destruction that had badly damaged the environment of Old Earth and destroyed an earlier Human interstellar civilisation that had once stretched across the galaxy.Under the Emperor's rule, Humanity would be restored, intellectually, spiritually and physically to the heights it had once known during the Age of Technology, and the shackles of darkness cast aside. The wars continued without relent until finally all of Old Earth's techno-barbarian factions, nations and fractured city-states pledged the Emperor fealty and at last Terra was unified for the first time in many millennia.It was not enough merely to secure military victory, however -- the betterment and restoration of Humanity required more. So it was that even before victory on Terra had been achieved the Emperor and those learned souls He had gathered to Him started to experiment with genetics. This was done first and foremost to stabilise the population and to recreate the species of Mankind as it was before the radiation storms and generations of atomic, biological and alchemical weapons had wracked the planet.Secondly, the creation of genetically-augmented transhuman fighters that had begun with the Thunder Warriors who had fought in the Emperor's armies during the Unification Wars continued apace into newer, more powerful creations, ultimately leading to the genesis of what would later become known as the Space Marine Legions. But in truth, the Emperor's greatest work was nothing less than the purging of Mankind's own genome, and its restoration to a baseline of what could be considered truly "Human" as that term had been defined before the Age of Strife.When the Emperor's Great Crusade moved out into interstellar space beyond the Sol System to restore the unity of Humanity across the galaxy in the late 30th Millennium, many lost Human colony worlds would be discovered where the Human genome had drifted, resulting in unusual physical manifestations. In most cases, these were nothing more than microevolutionary adaptations to the local planetary environments, and resulted in unusual skin tones, eye and hair colours and otherwise meaningless cosmetic changes.However, certain populations were discovered whose genomes had shifted in radical directions from the Human baseline, either through environmentally-derived mutation, xenos alterations or self-imposed genetic engineering. In these cases, the Emperor was forced to make a choice as to whether these mutants still retained the essential quality of Humanity, or had moved beyond the pale, having been transformed into what was actually a new species of xenos.In certain cases, such as those of the so-called "Abhuman" strains such as the Squats, Ogryns and Ratlings, the Emperor judged them to be recognisably Human enough to be incorporated as valuable members of Imperial society. But in other cases during the Great Crusade, many aberrant Human populations failed to make the cut, and were judged to have become so alien that they needed to be treated as true xenos, with the Space Marine Legions deployed to carry out the resulting purge.The galaxy would belong to Humanity, but it would be the same Humanity that the Emperor had loved and served for most of His long life.