Human

Humans (Homo sapiens) are a sapient species native to Earth. They are upright tetrapods who primarily use their forelimbs for object manipulation, with their rear limbs reserved for locomotion. They are one of the newest players in the larger meta-civilization of the Orion Arm, having achieved slipspace-using status independently in the 24th century. The largest and most notable human polity is the United Earth Government, often represented by its spacegoing and military arm, the United Nations Space Command.

Humans have been identified as Reclaimers by some Forerunner constructs, hinting at a possible connection between humanity and the ancient civilization. The exact nature of this connection is pending more research into the Halo Event and the nature of the galactic biodisplacements that occurred in the Conservation Measure.

Origins
The remote descendants of arboreal primates, humans supposedly evolved to their current form in the plains of Eastern Africa around 300,000 years ago. The early humans mostly lived as nomadic hunter-gatherers, mainly relying on their intellect, tool use and endurance as survival strategies. A range of related sapient and protosapient hominid species existed alongside Homo sapiens up until relatively recently, but these close relatives went extinct or hybridized with H. sapiens prior to the formation of large-scale civilizations.

Circa 97,445 BCE, humanity was indexed and archived on the Ark by the Forerunner known as the Librarian, alongside the entirety of Earth's sentient biota, in preparation of the imminent firing of the Halo Array. This discontinuity was previously noted in human science as the Ross-Ziegler Blip, and has since the Human-Covenant War been associated with the Conservation Measure and the Halo Event. This roughly coincided with humans' migration out of Africa, which eventually led to their settlement of most of Earth's continents. Beginning circa 10,000 BCE, a cascade of development known as the Neolithic Revolution precipitated the invention of agriculture and the creation of increasingly organized societies. This led to many of the formerly nomadic human communities settling down, and the increasingly available food sources enabled the growth of cities and populations, eventually forming entire civilizations with sophisticated cultures, religions and social structures.

Global period
Since the 19th century CE, human civilization began to advance rapidly with the Industrial Revolution bringing forth mass manufacturing and many new technologies, the effects of which resonated throughout the globe. This period was marked by rapid technological advancement and ideological experiments, which often proved a volatile combination. The First and Second World Wars in the first half of the 20th century saw death tolls unheard of in previous wars, along with humanity's entry into the Atomic Age with the development of the nuclear bomb. The end of World War II also saw the formation of the United Nations by the victors of the war, with the stated goal of preventing similarly destructive wars in the future; in several decades, the UN would become the preeminent forum of global dialog. The second half of the 20th century was marked by the the Cold War, a period of heightened tensions between two ideologically-opposed power blocs among the former Allies of World War II: the United States and the Soviet Union, along with their respective allies and proxy states. The ongoing arms race between the two polities also manifested as the Space Race, which saw humanity's first forays outside Earth's atmosphere. The Cold War came to an end with the collapse of the Soviet Union in 1991. Around the same time, the rapid advancement of miniaturized computing and the rise of the Internet as a global information network characterized what was known as the Information Age.

Space Age
The 21st century saw the beginnings of human space colonization, with the relatively rapid settlement of Luna and Mars in the first half of the century ushering in what was later fondly remembered as the Golden Age of Space Colonization - an unprecedented gold rush into the Solar System as numerous actors both corporate and national sought to exploit its near-infinite riches. The development of fusion power into a viable energy source provided an answer for Earth's energy crisis, though a civilization-wide fusion economy would take over a century to truly take off.

While generally remembered as a time of optimism and prosperity, this period was not altogether devoid of conflict. One of them most notable sources of geopolitical tension of the era was the Equatorial Scramble, the planet-wide transition of economic and strategic hotspots toward Earth's equator due to the growing demand for economical orbital launch sites and the subsequent struggle between major powers both old and new to control these hotspots. The waning years of this era also saw the eventual crumbling of the United States and the rise of the United Republic of North America in its stead as the preeminent North American power. A major war between NATO and China also led to the latter's diminishing on the global stage for some time. The first half of the 22nd century also saw the rise of various new powers in South America, Africa and Southeast Asia, as the old empires struggled with internecine issues. Meanwhile, the interplanetary colonies on Luna, Mars, the Jovian Moons and various asteroids took their first steps toward independence as their parent nations' influence on them weakened, though megacorporations remained a prominent influence in the colonies.

The Golden Age eventually came crashing down with the ZGene crisis and the resulting period of recession. Toward the mid-22nd century, humanity entered a downward spiral of economic and social problems, wars, and ideological radicalization, culminating in the Interplanetary War between the UN and several political extremist movements, most notably the Frieden and the Koslovics. The war led to enormous devastation on both Earth and the off-world colonies. Such was the magnitude of the crisis that most member nations of the UN willingly gave up their sovereignty in order to manage the crisis and its aftermath, leading to the formation of both the United Nations Space Command and the United Earth Government as pan-human military and governing bodies, respectively.

Colonial Era
The reconstruction process following the Interplanetary Wars lasted well into the 23rd century, historically known for its cultural and technological experimentation. The ongoing overpopulation on Earth prompted a continued flight to the recovering interplanetary colonies. The development of the fusion drive brought the once-faraway worlds much closer by shortening travel times, though the largest breakthrough by far would come in 2291 with the Shaw-Fujikawa Translight Engine, which enabled ships to traverse the subspatial domain of slipspace and thereby travel faster than light. By 2310, the first colony ship set off to other stars, and seventeen worlds were settled in the first half century of interstellar colonization. This process was not entirely without difficulty; the series of conflicts later known as the Inner Colony Wars wracked the nascent colonies in the later years of the 24th century. This was followed by another half century of relative peace and unchecked expansion later known as the Pax Humana, which gradually gave way for a period of tensions between the UNSC and the Colonial Military Administration as the former encroached on the latter's territory in the colonies.

Insurrection and first contact
Since the 2490s, humanity's nascent interstellar civilization began to spiral into a series of civil wars known collectively as the Insurrection, as growing numbers of Outer Colonies unsuccessfully sought autonomy from the United Earth Government, eventually resorting to armed insurgency. Throughout the early 26th century, hundreds of these brushfire wars were fought across human colonies with no end in sight. Some projected that, left unchecked, the ongoing development would spill over into a full-fledged interstellar war with a high likelihood of shattering human civilization and plunging the species into a dark age for decades, perhaps even centuries.

However bleak the present situation seemed, the conflict was quickly overshadowed when the alien hegemony known as the Covenant declared a war of extermination on humanity in 2525. For twenty-seven years, humanity fell back world by world, with billions of lives lost to the Covenant's ruthless onslaught despite fierce human resistance. At humanity's darkest hour, an unlikely and unforeseen chain of events ultimately allowed the species to narrowly avoid certain extinction. Shortly after the discovery of the ancient Halo Array, a civil conflict within the highest levels of the Covenant led to a major break-off faction of the hegemony allying themselves with the UNSC, enabling them to eliminate the Covenant leadership, throwing their remaining loyalists into disarray.

From the Ashes
By early 2553, humanity emerged from the war battered and beaten, but with the immediate existential threat to humanity eliminated. The leaders of the UNSC made a peace treaty with representatives of the Schismatic faction, who would eventually go on to become the Concord of Reconciliation - the UNSC's most powerful ally in the wider stage of the Orion Arm.

After a period of uncertainty known as the Years of Disquiet, humanity began to take steps toward recovery thanks to the efforts of the Phoenix Initiative, an interim coalition formed by the UNSC to facilitate reconstruction. This Reconstruction Period, as it was known, lasted from the 2550s well into the late 2570s and saw the reclamation of various lost colonies, the resettlement of various displaced populations, the gradual rebuilding of the UNSC's naval capability, as well as a number of technological advances. It also marked the beginnings of humanity's integration into the overall civilization of the Orion Arm and coming to terms with their status as but one species among many. Despite the alliance with the Concord, most humans continued to regard the ex-Covenant with various degrees of suspicion and animosity due to the war, a generational trauma that would not disappear until the long term. Some humans even acted on these impulses despite the UNSC leadership's attempts to maintain the truce. Meanwhile, rumors of humanity's special connection to the Forerunners along with the presence of the Ark portal on the human homeworld continued to be a source of unresolved tension to some ex-Covenant. Still, the most pragmatic members of both groups acknowledged the pointlessness of continued conflict and sought to build bridges to their former enemies; despite going against the wider populace's sense of justice, this approach as the guideline informing the Phoenix Initiative's foreign policy has been cited as having secured humanity's continued survival and sovereignty even as further challenges awaited on the horizon.

Humans are variously characterized by other species as persistent, inventive and resourceful, but also arrogant, myopic and boorish or culturally aimless. Within the Covenant, they are commonly compared to the Unggoy and especially the Kig-Yar. While increasing numbers of Sangheili came to respect humanity as worthy foes during the Human-Covenant War, many continued to have reservations about letting them remain independent of Sangheili rule. Humans' ubiquitous use of artificial intelligence remained a particular point of contention due to both longstanding Covenant strictures against AI and objections about humanity's perceived overreliance on machines.

Lifespan
Technological advancement has introduced various factors that influence the human lifespan. The first is medical technology. While "true" bio-augmentation is restricted by law, in-utero gene therapies designed to give one's offspring every possible edge while still staying within the commonly-defined boundaries of the human baseline are common on developed worlds. Coupled with such therapies being widely applied on the greater population in the past, people in developed regions of the Human Sphere are generally healthier and have much fewer congenital diseases or defects than people centuries earlier. This, in addition to various medical procedures during one's lifetime (e.g. flash-cloned organ transplants), means people generally stay youthful for much longer than before. As a result of these various factors, it is common for cognitive and physiological decline to be kept at bay up until well into one's 90s or even beyond. After a certain point, however, senescence is inevitable. People on Earth and many Inner Colonies frequently reach 120 or 130, while the oldest human recorded so far lived up to 173 years of age.

One key variable to note is the existence of cryosleep, which enables humans to "skip" technically indefinite periods of time in a state of cryogenic hibernation. Though usually used for long interstellar journeys to conserve resources, cryotubes have been known to be utilized by oft-eccentric individuals, sometimes called "time-tourists", to effectively skip years or decades of life in suspended animation and live out a few months or a year or two at a time in between. Time tourism is not very frequent due to the way it effectively removes one from normal society, but it happens often enough to have had some interesting implications on how e.g. banking and long-term investments work. Cryosleep cannot be entirely disregarded in the total count of one's lifespan as freezing/thawing cycles do put their own stress on the body, especially if done frequently. But it does effectively stop one's biological clock for the duration of the sleep, which has forced a distinction to be created between chronological and biological age. This difference can sometimes be quite drastic, especially with individuals who undertake frequent journeys through slipspace.