Precursor

The Precursors are a semi-mythological antecedent civilisation referenced in a handful of Forerunner texts. A pair of references within the aforementioned texts suggest that the precursors were viewed in a somewhat venerable light by the Forerunners, who believed the Precursors to have served as guiding figures to Forerunner civilisation in its earlier stages, teaching them, among other things, their guiding ideology of the Mantle of guardianship over other life. It is suggested by the Forerunners that the precursors had transcended beyond conventional intelligence, achieving a state variously translated as "transsentience" or "transsapience". References to such a state are difficult to decouple from myth, however. The Forerunners appear to have believed that they could have one day "followed in [the precursors'] footsteps" into a supposed ascendance, though the specifics of what this would have entailed remain elusive.

Whether the precursors existed at all is something subject to much debate. While there are several xenoarcheological sites predating the Forerunners throughout the explored portions of the Milky Way, attributing these to any given culture, much less a singular collective, is speculative at best. However, the Forerunners' existence as an offshoot of terrestrial humanity, as well as that of many other instances of anomalous out-of-place biota does imply the existence of at least one pre-Forerunner culture that tampered with the evolution of life on numerous worlds. The preeminent accepted theories place the precursors as those who moved original Forerunner populations away from Earth hundreds of thousands, perhaps millions of years ago, and may have guided these populations into technological enlightenment, alongside being responsible for many of the older ancient examples of biodisplacement encountered across the reaches of space.

While these theories have been commonly accepted by the scientific community, they remain largely that, as any solid details on the precursors are scattered and confused. Some references within the Forerunner archives contradict one another, indicating that belief in the precursors within Forerunner civilisation was not a universally-accepted practice - and that different groups within the Ecumene held opposing beliefs as to the origins of their own civilisation. Indeed, it is unknown as to whether the precursors constituted one species or multiple, or if they were a singular civilization at all.

The Forerunner notion of the Precursors as a single continuum of longtime galactic custodians has been embraced by some branches of Ancestral Displacement Theory. A longstanding problem among the scientific community is the "Dyson dilemma": if intelligent life is abundant in the universe and in our galaxy, and we now know it is, why have galactic resources not been more thoroughly exploited many times over? If sapience has emerged independently on numerous worlds since the ancient past, why has not a single culture already overrun the galaxy hundreds of millions, if not billions of years ago? Such questions were made even more puzzling by the discovery of slipspace (which made interstellar travel and communication vastly easier) and the ruins of past cultures on other worlds (which means that sapient technological life has arisen numerous times). We were not alone, and we were not the first. So why is so much of the galaxy relatively pristine and unexploited? Even the Forerunners, of which the most evidence survives, left relatively little behind considering what a truly long-lived galactic civilization could potentially do, and most cultures the Covenant discovered left an even smaller footprint, encompassing only small patches of the spiral arm.

A hypothetical answer to the dilemma is the position that there was or is a civilization of galactic custodians actively preventing any single culture from becoming too prevalent or technologically advanced, causing the collapse or withering of civilizations at risk of becoming preeminent either by force or via more subtle means. From the antecedent civilizations known, the Forerunners are already an anomaly in their extent. To such longtime custodians, the galaxy would have been akin to a zoo or a wildlife preserve, and any culture that began to rise over the others or exploit galactic resources via mass strip-mining or encasing stars in Dyson spheres would be a threat to galactic biodiversity. However, while this is a commonly theorized motive for "zookeeper" civilizations, it is by no means the only possible one. It is possible that such beings might have motivations and goals too esoteric for us to comprehend.

If the Precursors existed in the form the Forerunners believed, they could be the answer to the Dyson dilemma, acting as the galaxy's zookeepers for eons since the emergence of the earliest technological life. For hundreds of millions if not billions of years, they would have seeded many barren worlds with new life as well as branches of life plucked from other worlds, watched them develop, and pruned them if need be. After their disappearance, the displaced hominid population now known as the Forerunners happened to emerged as a preeminent power over a galaxy now bereft of its custodians, only to meet an untimely demise by their own hands. If this were the case, the current advent of galactic civilization in the Milky Way after the firing of the Halo Array would effectively be the first galactic meta-civilization since primordial times to arise to a galaxy free of an overarching custodianship.