Human

Humans, taxonomically referred to as Homo sapiens (Latin for "wise man") and known as hamanune (plural hamanush) in the Forerunner era, are a sentient species native to Earth. A part of the primate family, they are the only extant species of a formerly diverse genus of multiple species once classified as human.

By around 110,000 BCE, humanity had achieved a thriving interstellar civilization nearly on par with the Forerunners, although their catastrophic defeat in the Human-Forerunner War would see them reduced to a preindustrial state as hunter-gatherer tribes, forced to achieve technological sophistication again. Thanks to the efforts of the Forerunner known as the Librarian, however, humans were later elevated to the role of Reclaimers, intended to inherit the Mantle the Forerunners used to hold. Humanity would not begin to rise from the confines of their homeworld until nearly 100,000 years later, with the re-invention of space travel in the mid-20th century and the beginning of space colonization in the later half of the 21st century. Following a series of violent conflicts across the Sol system, humanity at large was brought under a single banner with the establishment of the Unified Earth Government in 2170. Over a century later, the invention of the Shaw-Fujikawa Translight Engine heralded a new golden age for humanity: no longer confined to their home system, humans spread across the neighboring stars.

At the end of the 25th century, this age of flourish was coming to an end, and the rising economic and political tensions across the colonies eventually culminated in a series of civil conflicts collectively known as the Insurrection. The war claimed millions of lives over the next three decades, but a far more dire threat loomed. In 2525, a theocratic alien hegemony known as the Covenant invaded the colony world of Harvest, beginning the apocalyptic Human-Covenant War. For nearly three decades, humanity, under the emergency military governance of the United Nations Space Command, was pushed back by the relentless Covenant war machine, until the tide turned in 2552. With humanity teetering on the brink of extinction, the discovery of a Forerunner artifact known as Halo set in motion a course of events which would lead to the fragmentation and eventual destruction of the Covenant.

Following the end of the war, humanity began to emerge as a major power in the known galaxy, with new technological developments sped up by the discovery of Forerunner relics. These developments may have elevated them from Tier 3 of technological advancement, on which they stood for most of the 26th century, to a higher Tier 2. Despite the defeat of the Covenant, humanity continued to be gripped by conflict in the post-war years. In addition to threats from within in the form of renewed dissidence across the colonies, a resurgent Covenant soon drove humans into a second conflict which also saw the reawakening of hostile Forerunner Promethean forces.

Prehistory


Modern humanity, Homo sapiens, is believed to have appeared in Earth's fossil record between approximately 100,000 and 200,000 years ago (an older branch of Homo sapiens known as Homo sapiens idaltu was believed to have lived as far back as 160,000 BCE). While the exact origin of humanity is a hotly contested paleontological debate, one theory is that the first humans evolved from a genus of upright ape-like hominids called Australopithecus (likely Australopithecus afarensis).

The origins of humanity lay in the ancient race of beings known as the Precursors. Responsible for seeding the galaxy with life, the Precursors genetically engineered early humanity along with many other species in the galaxy, including Forerunners, a would-be rival species to humanity. The Precursors intended humanity to inherit the Mantle, their assumed role of guardianship for all life in the galaxy. The Forerunners refused to accept this decision and subsequently rebelled against the Precursors. After exterminating the Precursors to the point of extinction, the Forerunners claimed the Mantle for themselves, using it not only as the basis of their society but also as justification for securing their own dominance for millions of years.

Homo sapiens is not the only species of human to have evolved on Earth, but they have either displaced or outlasted all other branches of the genus Homo, all species of which were once collectively known as "humanity". In prehistoric times, there was significant contact between anatomically modern humans and other members of the genus, both cultural and genetic, coexisting with species such as Homo erectus, neanderthalensis and floresiensis, and, based on residual genetic evidence, interbreeding with other species (1-4% of the DNA in European and East Asian humans is Neanderthal, while Melanesian people have 4% of Denisovan blood). Modern humans usually stand 6' tall, though this varies depending on nutrition, genetics and other factors. Members of the species, like some Covenant species, are four-limbed and bipedal, which enables them to walk upright on two legs and use their arms and hands (including opposable thumbs) to hold and manipulate objects such as tools.

Early civilization and Forerunner involvement
Humanity achieved an advanced state early in its history, over 150,000 BCE, eventually reaching a level of technological sophistication close to that of the Forerunners. Humanity resented Forerunner dominion over the galaxy, and as a result expanded their civilization outward along the Orion Arm and across the galactic margin. At one point, humanity formed an alliance with the San 'Shyuum and later warred against the nascent Flood. While humanity lost a third of their population, the Flood was eventually driven out of the galaxy. However, the conflict led to a war with the Forerunners, a war which humanity lost. As punishment, the humans were stripped of their technology, nearly all evidence of their civilization was erased from the galaxy, and the scattered remnants of their species were exiled to their homeworld, reduced to a pre-technological state from which they would be forced to start again.

Humanity was one of many species indexed by the Librarian and preserved during the Conservation Measure. Viewing humanity as special, the Librarian imposed a geas upon the species, which has been said to have greatly affected their development; in particular preparing humans for their role as successors to the Forerunners as stewards of the galaxy. Although the bulk of the indexed human population - as well as many of the formerly diverse human species - were lost when the Ur-Didact used the Composer on the inhabitants of Omega Halo, the Librarian and her successor, Chant-to-Green, managed to save enough specimens to successfully revitalize Homo sapiens and several other species. Following the firing of the Halo Array, the surviving humans were returned to Earth.

Post-Array recovery
The development of human civilization as humans recognize it today started from the ability to harness the growth cycle of plants, producing edible food-energy in a systemic fashion. This time is referred to as the Neolithic Revolution, which occurred first on Earth over 10,000 years ago and soon spread to disparate human groups. The stability that came from systemic agriculture allowed for more permanent settlements and the development of ever-more-complex tools to further benefit the members of the species.

Innovated toolmaking and the domestication of other species on Earth gave human populations greater and greater power to expand their populations, and trade ensured the diffusion of new technologies to adjacent groups. These exploding populations led to the formation of the first genuine civilizations over 8,500 years ago. The sites of such early cultures are believed to have formed in Southwest Asia and Asia Minor, and appeared elsewhere soon after. The infrastructure of civilizations continued to expand and grow in complexity as innovative technologies and larger populations allowed for increasing food-energy availability. Economic, political and scientific advancement continued to quicken as this species was able to automate many tasks in the Industrial Revolution.

This automation gave birth to the Digital Revolution, in which computing machines allowed scientific discovery and technological development to accelerate with explosive speed. Larger urban centers and tools for civilian and military uses were able to develop, as were more modern economic and political systems. As these systems developed further, the species was able to enjoy longer, more pro-creative, and more comfortable lives, virtually impervious to other creatures from whose midst they sprang. Thus-unchecked, human population growth eventually led to the presence of several billions more humans on Earth than could be comfortably sustained, ultimately leading to a high demand for humans to expand out-world.

18th-20th century
The 18th through 20th centuries were times of drastic change for countries known as the "Industrial Revolution". As an unintended result of major political and economic ramifications due to the rise of constitutional governments and refined capitalist resource management techniques, important inventions such as the automobile, electrical devices like the radio, and aircraft went into widespread use at previously unheard of rates for human innovations. Revolutionary progress in humanity's understanding of medicine and chemistry was also being made during this era of turning points. Such important chemical engineering advancements included anesthesia which dramatically enhanced all surgical practices, and plastics that could cheaply fulfill an enormous amount of material roles (with the better preservation of food being one of its greatest functions). Prior to such chemical and medical advances, average humans at the beginning of this time span could expect a lifespan of approximately 45 years, but towards its end, thanks to the introduction of antibiotics and other medicines combined with better food production and preservation, the age-old scourge of widespread plague and starvation was becoming virtually a thing of the past, and enabling people to live well beyond 80 and even into 100 years of age.

Essentially, Mankind was growing ever more efficient in how it applied itself to previous sciences and arts, and the art of the military would prove no exception to this pattern. There would be a rapid change in armed conflicts, starkly different from the primitive melee-oriented wars of the past; after two massive wars within the first 50 years of the 20th century, humanity saw the invention of such technologies as superior firearms and automatic weapons, radar, tanks, missiles, jet engines, and ultimately the atomic bomb, which became the most powerful weapon then known. Atomic bombs ultimately led to nuclear warheads, which eventually became key components in human arsenals in the brutal war against the Covenant. In the next 60 years the superpower nations of the United States of America and the Union of Soviet Socialist Republics (succeeded by the Commonwealth of Independent States) became highly competitive, leading to a period of military and cultural tension known as the "Cold War"; an arms race by which the lethality of humanity's relatively new warfare technologies would be further refined upon in their destructive potential and precision, complimented with ever evolving battlefield doctrines and tactics as both nations sought to intimidate the other, with the newly developed nuclear weapons playing a large part in this period. In the 1950s, the Soviet Union launched the earliest satellite and sent the first human, Yuri Gagarin, into space, officially making humans spacefaring and entering Tier 5 in the Technological Achievement Tiers. The United States successfully placed the first human, Neil Armstrong, on the Moon, and eventually surpassed the Soviet Union's spacefaring and military production capabilities, leaving their doctrines as the ones that would heavily influence the UNSC in later centuries.

Additionally, with the creation of the Internet in the late 20th century, achievements from that era would dramatically revolutionize communication and data processing, further streamlining mankind's rate of technological progress. World politics also changed, with the early history of the United Nations beginning during this time period. The religiously neutral nature of many of these constitutional style governments also saw a relative diminish in the weight of ideological dogma, with scientific and logical explanations for phenomena and methodology rising in importance. Religion would remain a staple of human societies insofar as advocating personal ethical codes, though unlike the Covenant its primary influence was no longer that of a mere framework to justify a large hierarchical system of differing castes and birthrights.

Space colonization
The human species was able to explore the space immediately surrounding their home planet in the 20th century, as the population began to advance beyond the capacity of the planet to comfortably sustain their civilization. The subsequent conflict over resources, economics, religion and politics on Earth gave way to numerous wars. Furthermore, these tensions put great pressure on the species in the late twenty-first and early twenty-second centuries, and the transnational mediator organization known as the Unified Earth Government engaged in more frequent space colonization and sought to represent the entire species, even though no one state ever previously ruled the entire human race. The Interplanetary War in the 2160's marked a major shift in humanity's governance: after a violent conflict spanning the Solar System, the UEG was formed into a true governing body in charge of all human nations. While growing overpopulation on Earth continued to pose challenges for the new government, the development of Slipspace travel in 2291 helped the UNSC engage in spreading the human race beyond their home solar system, relieving the serious ecological pressure on the home world.

This expansion was to usher in promising new opportunities for humanity, as some of these colonies, such as planet Reach with its bountiful titanium deposits, could offer abundant stores of raw materials that may had otherwise been considerably unique and scarce on Earth. With the initial advent of interplanetary trade driving down the costs of what may had once been an expensive implementation of their technology - such as the forging of space-worthy ships and naval vessels - the effects from these carefully implemented first colonization projects helped to ensure that interstellar trade, travel and communication were to be more commonplace amongst the general populace in the ensuring centuries, eventually granting humanity the capacity to establish colonies at enhanced rates. In the background, the progress of human civilization was being subtly manipulated for hundreds of years by the Assembly, a shadowy collective of AIs committed to humanity's survival.

The Insurrection
After over a century of prosperous expansion, humanity's populations had spread relatively thin across hundreds of worlds in a volume of space dozens of light-years across. The colonies had become divided among the Inner and Outer Colonies, the former representing the first established, stable and wealthy populations and while the latter were responsible for supplying a large portion of the resources that allowed the core worlds their high standard of living. As predicted by sociologist Dr. Elias Carver, a buildup of discontent among the Outer Colonial populations eventually culminated in the onset of numerous brushfire wars across the Outer Colonies which would come to be known collectively as the Insurrection. The UEG's fear of these civil conflicts escalating into a projected apocalyptic war between the Inner and Outer colonies to the creation of the ORION and SPARTAN-II supersoldier programs, along with extensive UNSC military campaigns across the colonies.

The Covenant War
After decades of internecine conflict, humanity as a whole was forced into their first major war against an outside opponent when they were discovered by the genocidal alien hegemony known as the Covenant. As the decades-long war wore on, the human species gained the reputation as a worthy adversary against the Covenant, despite the fact that they were technologically and numerically inferior. Despite the fact that humans could hold out and even defeat the Covenant on ground combat, the Covenant could in turn withdraw to space where they had virtually undisputed supremacy and would be capable of glassing the planet.

Humans have been able to show great bravery when facing insurmountable odds. Some of the members of the Covenant wondered why their leadership had refused to allow the humans to join them, as they had been able to hold steadfast even when outmatched in almost every way. However, despite great courage and tenacity, the future seemed dark for the survival of the human race as the Covenant continued to methodically exterminate their colonies, marching ever closer to Earth, eventually discovering and invading it on October 20, 2552. In the ensuing battles over possession of Earth, humanity suffered heavy casualties.

Post-war
Following the final battle of the war on December 11, 2552, the Human-Covenant War ended in a victory for humanity and their newfound Sangheili allies - the majority of the Covenant military having been defeated at Delta Halo by the Sangheili Fleet of Retribution, while the rest were annihilated by the joint Elite-UNSC forces at the Ark. This victory came in time to save the human home world, thanks chiefly to the actions of the Arbiter and Spartan John-117. The Human-Covenant War was officially declared over on March 3, 2553, when a memorial service was held near Voi, Kenya, to those fallen during the 27 years of fighting.

In her inaugural speech in January 2553, President of the Unified Earth Government Ruth Charet outlined humanity's future and foreign policy, promising that they would rebuild as well as stating that humanity would now reclaim their "rightful place in the universe". While humanity was willing to coexist with other species, they would never again allow themselves to be the victims of alien aggression. While the official stance within the government and the military was to build peace with the Sangheili, the UNSC's Office of Naval Intelligence covertly worked to neutralize the Sangheili, whom they considered the most acute threat to human primacy.

Not long after the end of the war, a new Covenant order led by Jul 'Mdama initiated their own campaign against humanity, beginning a new conflict with the alien collective. However, the UNSC fared significantly better against this significantly weaker incarnation of the Covenant, with improved assets and technology, such as the and the SPARTAN-IVs, at their disposal proving an advantage for the recovering UNSC. In 2557, after both parties stumbled upon the shield world of Requiem, the conflict was joined by Promethean forces led by a surviving Forerunner known as the Didact, who once commanded the Forerunner armies against prehistoric humanity in the Human-Forerunner War. Allied with the modern Covenant, the Didact defied the Forerunners' decision to pass down their Mantle to humanity by continuing his previous genocidal campaign. During the conflict, contact was also made with mankind's ancient benefactor, the Librarian, who had archived her personality and memories to assist humanity to guide them in their ascension to the Mantle. The Didact attempted to digitize humanity with the Composer, but was defeated at the last minute by John-117 and his AI Cortana, though thousands of human lives were lost.

Technology
Prior to the human-Forerunner wars, humanity had achieved a remarkably advanced technological state, having developed interstellar travel, colonized thousands of worlds outside of their solar system, and even having an understanding of Precursor technology. However, all records and examples of this former technology were obliterated following their war with the Forerunners. Humanity managed to develop rudimentary technology such as steam power roughly nine thousand years after their defeat. Unfortunately, this technological and cultural development proved to be in vain: during a phase after the Conservation Measure's reintroduction stage, aptly termed as the dark time, the species regressed back into hunter-gatherers for over 90,000 years until the development of the modern human civilizations first began.

In early stages, human technology and knowledge advanced through simple trial and error in an inefficient manner, hampering faster progress. Although humans had developed writing very early on in their history, it wasn't until the invention of printing that information and ideas could be mass-communicated in an effective manner. The development of the scientific method in later conjunction with improved and more efficient capitalistic resource management techniques during the lessons of the "Industrial Revolution" resulted in stark accelerations in the development of technologies and the acquisition of knowledge. New technologies were experimented and explored with advanced knowledge of underlying principles as talented individuals were better organized and better supplied, allowing extremely accurate and fast improvements to be made with minimized trials and costs. Such methods of thought and organization are a hallmark of humanity which differs from the Covenant who, lacking proper researching methods, would simply copy and reverse-engineer technology from ancient Forerunner artifacts via the Huragok, whilst generally having no understanding of the underlying concepts themselves. Thus it it was said that the Covenant are "imitative" while the humans are "innovative" as the war progressed.

By the 26th century, human technology has not advanced equally for every concept previously explored. The most basic technologies (such as the ballistic weaponry and the wheel) have undergone few principal changes, the explanation for this being their proven reliability over centuries of use. The technology worked and so did not require heavy alteration or major changes. However, certain significant advancements have been made in other fields, such as Shaw-Fujikawa Translight Engines that allow ships to reach other star systems, as well as the creation of highly sophisticated AIs that can serve to fulfill a versatile amount of roles. In addition, humans have also developed various forms of nanotechnology which allows many advances impossible with conventional engineering.

Human technology has undergone further advancements as a result of the reverse-engineering of Covenant and Forerunner technologies at the close and aftermath of the Human-Covenant War. These include, among other things, significant improvements in slipspace navigation and velocity as well as improved offensive and defensive weapons technologies, such as the more widespread adoption of energy shielding.

Artificial intelligence
Human AI constructs can be grouped into two main categories; "dumb" and "smart" AIs. These labels are technically misleading, as both types are extremely intelligent, but dumb AIs are only capable of learning about subjects within their designated area of expertise, whereas smart AIs exhibit much more human-like characteristics, such as emotions, creativity and intuition. Smart AIs can only be created by scanning a human brain and replicating the neural pattern to a digital storage system known as a Riemann matrix, which allows the AI to develop its own neural linkages. However, this ability comes with a price; as the linkages increase in density, after seven years of operation, the AI will descend to a terminal condition known as rampancy. Various solutions have been attempted to counter this issue, but none are known to have been effectively implemented.

Weapons
While still primarily based on projectiles and chemical reactions, human weapons are more advanced than the weapons of the 21st century. They come with a variety of electronic gadgets such as ammo readouts and are significantly more reliable, seldom malfunctioning. They are also generally immune to electromagnetic pulses. Still, there have been many advanced developments, such as electromagnetic accelerator weapons. The most prominent of these is the Magnetic Accelerator Cannon, used as the main armament on UNSC warships, and in smaller form in ground-based weapons. Another electromagnetic weapon system, known as the railgun, is used to a lesser degree. There have been developments in energy weapons such as the Spartan Laser and the pulse lasers used on UNSC prowlers.

One of the largest breakthroughs came in the mid-20th century where humans discovered that nuclear fission and fusion can be used as a weapon to cause a large explosion. By the 26th century, there are several types of nuclear weapons in the UNSC's arsenal, intended for both atmospheric and exoatmospheric use. Innovation in this area would also converge in the creation of humanity's most devastating weapon during the war effort, known as the NOVA bomb.

Vehicles
Though human vehicles still rely on crude wheeled or continuous track motion for locomotion, UNSC vehicles are still extremely advanced, incorporating high-strength materials with precision engineering to improve mobility and durability, while often mounting a variety of weapons or equipment to increase their flexibility. Most have switched from fossil fuels to hydrogen-fuel cell engines or at the very least use hybrid-electric engines for enhanced fuel efficiency. The most powerful of human vehicles usually run on continuous tracks that allow them to better distribute their weight over uneven ground and to better grip uneven terrain thus allowing for the vehicles to go places where other wheeled counterparts could never, but the vehicles are usually heavier than their wheeled counterparts.

Most UNSC aircraft are designed with Vertical Take-off and Landing capabilities, using adjustable jet engines for lift and thrust. It is possible that some incorporate lifting body principles.

Medical advances and biotechnology
Humanity has mastered a number of medical technologies, improving the quality of life in general but also providing many military applications. Among the most prominent is flash cloning, which allows the re-growth of almost any body part and is often used to replace damaged or lost organs. Lost limbs may also be replaced with advanced mechanical prosthetics. Humans have been effectively immunized against some conventional diseases, such as cancer. Though isolated cases of cancer still occur, they can be easily treated. On long slipspace voyages, humans use cryo chambers, allowing the occupant to enter cryonic suspension which effectively stops biological aging for the duration of the journey. These and many more advances have continued to push human longevity beyond prior estimates; with flash-cloned organ transplants, coupled with time spent in cryosleep, one's biological age may be decades less than their chronological one.

The use of sterile field generators means that surgery is not only safer to perform, with a greatly reduced risk of infection, but is also able to be performed in the field. Even critical injuries can be treated with relatively limited facilities; with sufficiently sophisticated equipment such as that of the, the resuscitation of individuals traditionally considered dead is not unheard of. Biological death can also be delayed by placing an individual into cryonic suspension until proper medical care can be provided. A number of synthetic compounds have been developed to allow more rapid recovery from injuries or to ease the treatment of patients in general; these include biofoam, bone-knitting polymer, and polymerized hemoglobin.

Humans have also adopted a variety of bioengineering and augmentation technologies. The first widespread use of biochemical augmentation was implemented in the early days of human space travel, to help humans adjust to long-duration spaceflight and different planetary environmental conditions. Subsequently, human enhancements saw military application in the first interplanetary conflicts. While human enhancement has been commonplace for centuries, more extensive augmentation or experimentation has been limited due to ethical concerns. An exception to this are the biochemical and cybernetic augmentations used in the SPARTAN programs, which represent the peak of human medical technology in the field of biological enhancement. Human rebels also use "rumbledrugs", which degenerate the user's body but grant them superhuman abilities for a short time.

Space-faring
During the mid-20th century, humanity experimented with rocket technology using it to build satellites and visit and subsequently colonize the Moon and beyond in the latter half of the 21st century. With the advent of Slipspace engines allowing faster-than-light travel, the UNSC was able to expand well beyond the confines of the Solar System, colonizing hundreds of worlds. UNSC freighters transport food and goods between colonies, while UNSC Navy warships protect trade routes from pirates and defend colonies from enemy assault. Space elevators are used on many worlds to provide orbital transport.

Human spacecraft are typically equipped with nuclear fusion engines for subluminal propulsion. These drives provide thrust via expelling either the fusion reactor exhaust or some other form of reaction propellant through a series of thruster nozzles. They are capable of remarkable thrust, allowing ships to cross interplanetary distances in a matter of hours, although gravity-assist maneuvers are commonly used to an advantage. Rocket thrusters using triamino hydrazine as propellant are used for attitude control and small-scale maneuvering.

While the weapons and combat abilities of human spacecraft were still very limited by the time of the Human-Covenant War, the reverse-engineering of Covenant and Forerunner technologies has subsequently granted humanity multiple advances in these technologies.

Gravity technology
As of the 26th century, humanity employs a variety of gravity-manipulating technologies, including two forms of artificial gravity aboard spacecraft and space stations. The first is a system of rotating "carousel" sections which generate an approximation of gravity through centrifugal force. Humanity has also developed a form of artificial gravity which does not require moving parts, but this technology consumes enormous amounts of power and spinning sections are generally regarded as being more efficient. Some UNSC ships, such as Phoenix-class colony ships or UNSC frigates are equipped with a form of anti-gravity technology, as evidenced by their ability to operate in a planetary atmosphere without the use of thrusters. Not all ships are equipped for atmospheric operation, however. Anti-gravity is not typically implemented on craft smaller than warships; conventional engine systems are used to produce lift instead.

Communications
By 2552, humanity has managed to develop a communication system which enables instantaneous superluminal communication. In effect, this allows instant data transfer and real-time conversation over interstellar distances. Prior to this, the primary form of long-range communication was limited to manually delivering the messages to the recipient by carrying messages aboard starships. For short-range communications, humanity employs conventional radio, as well as tight-beam laser and maser-based systems. The various human communication systems are commonly shortened to "COM".

Population
Earth's population was deemed overpopulated in the 22nd century, jump-starting the colonization programs at the time. Despite the colonisation efforts made to resolve the overpopulation issue, Earth's population still remained in the billions. In 2511, Dr. Halsey and UNSC estimated the universal human population to be around 39 billion, of which many were unrecorded by colonial infrastructure. In October 2552, Cortana said that humanity suffered 23 billion casualties throughout the course of the Human-Covenant War, putting the surviving human population around 16 billion. However, the actual population may be larger as it doesn't take into account the population growth from 2511 to 2525, or the population growth from 2525 to 2553 that was overshadowed by the comparatively larger number of deaths.

There has been some discrepancies regarding the population of Earth after the Human-Covenant War. According to the Bestiarum, the human population on Earth was stated to have been reduced to 200 million near the end of the Human-Covenant War, while the Halo Encyclopedia merely mentions the population to have been cut in half at the start of the Battle of Earth. The Encyclopedia does not however specify whether it means half of Earth's population were killed, or if a significant number were evacuated. However, the latter is more probable, as the statement is in regard of the situation at the beginning of the battle and the Covenant did not commence planetary bombardment—which was said to have produce "extreme" casualties—until the last days of the engagement. In a ViDoc, Halo 3's art director Marcus Lehto briefly mentioned the casualty count during the Battle of Earth as being in the millions.

Anatomy and physiology
Humans are mammals, and are closely related to other large apes on the planet Earth. Like all placental mammals, they are warm blooded and give birth to live offspring, and nourish their offspring with milk. They have five fingers, one being an opposable thumb. This hand structure aided them in making tools early in their history.

Unlike Sangheili, their circulatory system is closed and consists of one heart and a network of blood vessels. They have red blood due to their iron-based hemoglobin, as well as two lungs which breathe mainly a nitrogen-oxygen based atmosphere. Externally they have more hair than most Covenant species, but not nearly as much as Jiralhanae. They have an average sense of sight, but compared to Covenant species a poor sense of hearing and smell. They are omnivorous, meaning that they will eat both meats and plants, as well as consume high calcium foods, such as the milk of other animals.

Their bone structure is calcium-based and is designed to withstand moderate stresses, but is generally weaker than the skeletons of Jiralhanae and Sangheili. Their muscular system is, on average, also weaker than most large Covenant species. In theory at least, physical conditioning can still negate this somewhat as even a standard UNSC marine can be witnessed flipping a turned over vehicle, and with the right enhancements and equipment, overcome their physical disadvantages to an even further extent as demonstrated by the Spartans. If in extreme distress, humans can tap into hidden reserves of energy, known as an adrenaline rush thus giving them drastically increased strength. This response is known as the "Fight or Flight" reflex.

Connections between the Forerunners and humans
Until recently, it was popularly theorized among the Halo community that the Forerunners are the ancient ancestors of the human species. Evidence of possible descent include the fact that only humans could activate certain Forerunner technology, as well as multiple comments made by 343 Guilty Spark during the Halo trilogy. With the story of human-Forerunner relations being revealed in The Forerunner Saga, it is now known that humans and Forerunners are two distinct species, and that humans are not direct Forerunner descendants, although they are noted to have a strangely similar genetic code. The Forerunners themselves were intrigued by the similarities between their own race and humanity. Because of their genetic and physical similarities, some Forerunner scholars theorized that humans were a kindred species, created by the Precursors in their own image, just as the Forerunners believed themselves to be.

The Forerunners chose humans to become the inheritors of their technology along with Forerunners' sacred Mantle, which they formerly believed to have inherited from the Precursors. The Forerunners re-encoded certain aspects of their technology (e.g. the activation index) to only respond to human DNA to stop their advanced technology getting into the hands of other races. In a mixture of guilt and hope, they passed the torch to humanity, in hope that in the future they would defeat the Flood again, which with some help, John-117 did. The Librarian imprinted the humans with a geas, information hidden deep in the genetic code and passed on throughout generations. According to the Librarian, this imprint triggered the development of many technologies which proved critical to the survival of humanity after their contact with the Covenant, as well as containing several latent abilities. This may also explain the "natural" understanding of Forerunner interfaces some humans have demonstrated despite having no prior contact with Forerunner technology. Human memories and patterns extracted during the Conservation Measure were also implanted into future generations.

Despite this, some Forerunner AI constructs seem to regard humans as Forerunner. In Halo: Combat Evolved, 343 Guilty Spark confuses the Master Chief with a Forerunner (specifically, the IsoDidact), referring to conversations they never had. In Halo 3, 343 Guilty Spark tells the Master Chief: "You are the child of my makers. Inheritor of all they left behind. You are Forerunner!" Quotes by the Gravemind spoken in Halo 3 also seem to reinforce the connection between humans and Forerunners, for example: ''Child of my enemy, why have you come? I offer no forgiveness; a father's sins pass to his son.''

During the events in Halo: Contact Harvest, a Covenant missionary ship traveled the edge of Covenant-controlled space and discovered a planet that was covered with Forerunner "Reclamation" glyphs, who were actually the humans. Later, a report of the planet's glyphs was sent to the Vice Minister of Tranquility. He took the information to the Minister of Fortitude and he went to see the Oracle (the Forerunner AI, Mendicant Bias, in the Dreadnought). Upon activation of the "Oracle", the AI proclaimed, "FOR EONS I HAVE WATCHED. LISTENED TO YOU MISINTERPRET. THIS IS NOT RECLAMATION. THIS IS RECLAIMER. AND THOSE IT REPRESENTS ARE MY MAKERS. I WILL REJECT MY BIAS AND WILL MAKE AMENDS. MY MAKERS ARE MY MASTERS. I WILL BRING THEM SAFELY TO THE ARK."

Truth, believing that the humans were actually Forerunners (rather than their inheritors), became panicked and realized that this information could destroy the foundation of the Covenant and, with it, his power. Utilizing his power as High Prophet, Truth proceeded to launch a massive religious crusade against humanity, the Human-Covenant War. At the end of the war, when Truth was preparing to force Sergeant Major Avery Johnson to activate the Halo Array, he still believed humans to be the Forerunners' literal descendants, saying "Your forefathers wisely set aside their compassion. Steeled themselves for what needed to be done. I see now why they left you behind. You were weak. And gods must be strong."

The Iris viral campaign, the comic Halo 3: Cradle of Life and the Terminals of Halo 3 also explained that the humans were not direct descendants of Forerunners; instead, the Forerunners rediscovered humanity on a planet in a "perilous location beyond the line" (Maginot Line, meaning that Earth was outside of the Forerunners' protection). However, this was overridden by Halo: Cryptum, as the novel reveals that humanity's homeworld was known to the Forerunners thousands of years prior to their war with the Flood.

List of appearances

 * Halo: The Fall of Reach
 * Adjunct
 * Halo: Combat Evolved
 * Halo: Combat Evolved Anniversary
 * Terminals
 * Halo: The Flood
 * Adjunct
 * Halo: First Strike
 * Adjunct
 * Petra
 * Tug o' War
 * i love bees
 * Halo 2
 * Conversations from the Universe
 * Halo Graphic Novel
 * Armor Testing
 * Breaking Quarantine
 * Page 122
 * Second Sunrise Over New Mombasa
 * The Last Voyage of the Infinite Succor
 * Halo: Ghosts of Onyx
 * Iris
 * Halo 3: The Cradle of Life
 * Halo: Landfall
 * Halo: Arms Race
 * Halo: Combat
 * Halo: Last One Standing
 * Halo: Uprising


 * Halo 3
 * Halo: Contact Harvest
 * Halo: The Cole Protocol
 * Halo Wars: Genesis
 * Halo Wars
 * Halo: Helljumper
 * The Life
 * Halo 3: ODST
 * Sadie's Story
 * Halo Legends
 * Homecoming
 * Origins
 * Prototype
 * The Babysitter
 * The Package
 * Halo: Evolutions - Essential Tales of the Halo Universe
 * Blunt Instruments
 * Dirt
 * From the Office of Dr. William Arthur Iqbal
 * Headhunters
 * Human Weakness
 * Midnight in the Heart of Midlothian
 * Palace Hotel
 * Pariah
 * Stomping on the Heels of a Fuss
 * The Mona Lisa
 * The Impossible Life and the Possible Death of Preston J. Cole
 * The Return


 * Halo: Blood Line
 * Remember Reach
 * Birth of a Spartan
 * Patrol
 * Deliver Hope
 * Halo: Reach
 * Data pads
 * Dr. Halsey's personal journal
 * Halo: Fall of Reach
 * Boot Camp
 * Covenant
 * Invasion
 * Halo: Cryptum
 * Halo: Glasslands
 * ''Halo Living Monument
 * Halo: Primordium
 * The Commissioning
 * Halo: The Thursday War
 * Halo 4: Forward Unto Dawn
 * Scanned
 * Halo 4
 * Terminals
 * Spartan Ops
 * Halo: Silentium
 * Halo: Rebirth
 * Halo: Spartan Assault
 * Halo: Initiation
 * Halo: Escalation
 * Halo: Mortal Dictata
 * Halo Xbox One