Out-of-place biota

Out-of-place biota is the occurrence of organisms on worlds where said organisms clearly did not originate. The phenomenon was first recorded with terrestrial biota in the early 24th century with the onset of extrasolar colonization, with the earliest known example being the presence of flora and fauna that unambiguously share a common ancestor with Earth counterparts on Strauss' World in the Tau Ceti system. While initially controversial and subject to heated debate, the most likely explanation the scientific community has since come to favor is the translocation of organisms and ecosystems by one or more spacefaring civilizations in the distant past, perhaps for the purposes of terraforming, preservation or experimentation. It has further been postulated that said civilization(s) may have wished to avoid direct interference on the planet of origin (in this case Earth) to allow the evolution of life to take its natural course there.

The phenomenon remained one of the strongest cases for the existence of extrasolar intelligent life prior to the contact with the Covenant. While the existence of out-of-place biota has largely passed into the realm of mundane everyday knowledge as of the 26th century, it became a cultural sensation at the time of its discovery and remained at the forefront of public discourse for over a century, as evidence for "ancestral meddling" grew by the day with more and more irregularities (real or imagined) being discovered as humanity's reach expanded throughout space. Early examples in particular were often subject to intense scrutiny after several hoaxes came to light, most famously a half-baked attempt by a terraforming corporation to draw interest to Roswell. Out-of-place biota has also fueled numerous conspiracy theories and cults, including the infamous Other Homeworld Theory. Its discovery also marked a resurgent interest in 's 21st-century, which contemplated the existence of divergent branches of humanity around other stars, or even terrestrial humans themselves having originally evolved elsewhere; however, the latter interpretation is now widely rejected due to the overwhelming evidence to the contrary. The phenomenon also inspired art and entertainment; the discovery of "lost colonies" of humans in particular was a staple of 24th- and 25th-century science fiction.

The phenomenon has also been well documented by the Covenant since their early spacefaring history. While the Covenant universally attributed it to the Forerunners, some human scientists in the post-war era have been skeptical of this interpretation, as some of the displaced biota appears to have diverged from its origins long before the Forerunners are known to have been active in the galaxy.