For those who have not completed Xenoblade Chronicles X, this page may contain spoilers regarding the plot. Discretion is advised.
The Samaarians engineered other races, including the Ganglion and the Zaruboggan. This was not an altruistic act of creation—these races were made to serve Samaarians, and were built with failsafes to ensure that servitude.
To control the Ganglion, the Samaarians encoded a failsafe directly into Samaarian (human) DNA: If the Ganglion ever turn against their Samaarian makers, then mere exposure to human DNA is lethal to them. Since the Ganglion betrayed the Samaarians long ago, their race has a visceral hatred for humans and a fear of ever coming into physical contact with them again.
Likewise, the Zaruboggan were made to clean up the pollution ("voltant") that Samaarian civilization left in its wake, with the Zaruboggan worshiping their Samaarian creators as the mythical benevolent deity Golbogga that created all their voltant. The Zaruboggan physically require a steady diet of voltant just to survive, and a clean (voltant-free) environment is lethal to them, thus tethering their fate to that of the Samaarians. The Zaruboggan were only able to survive because their homeworld Bedun had served as a massive toxic waste dump with a vast supply of readily available voltant, nourishing them up until the Ganglion conquered it. When the last surviving Zaruboggan fled the Ganglion and were accepted into New Los Angeles as xenoform refugees, they delighted in the pollution the human city continually created, considering humans as generous in their supply of voltant as the Golbogga they worship, ironically resuming with those humans the same symbiotic relationship the Zaruboggan once had with the Samaarians who created them.
The ancient Samaarians all but disappeared, leaving only humans living on Earth in ignorance of their race's origins. The Samaar Federation they founded continues to function as a polity, but comprised of other alien species including the Ganglion. The Ganglion believe that Mira, or somewhere else within its associated space-time anomaly, may have been the original Samaarian homeworld, and by extension the original human homeworld before Earth.