After a while purely scientific statements of genetic and genealogical origin point grow somewhat dreary, no? In any case, these less factual ideas might inform some kind of cultural perception, perhaps even a religion of sorts.
Origins, or Otherwise
1- From deep unground, in warm pools of primordial water heavy with silt and life, did the physical forms of these people grow. And when they grew too large to fit, and felt their bodies ache with stillness, did they claw at the earth above and drag themselves to the dusty surface to be burned by the suns.
2- Upon the strings of the still universe did the God play the first song, a perfect one that echoed in every space until the God heard it a hundred-thousand times over. And when it heard its own song, it found revisions could be made—but had since forgotten how to play; so the second song had a new ending, which caught at itself and lit the stars and ripped open the emptiness between. This displeased the God, who attempted again; so the second song was played backwards, which jarred at the echoes and sent small stones around the stars. The third song, played in a low key, awoke the stones and their inhabitants. The fourth song, played in a high key, set time in motion with its last notes. And so the God crafts the fifth song to perfect the mistakes.
3- When the last of the Old Ones died at the core of the world, their servants took the corpses and threw them inside vast ovens for fuel. Upon those ovens cook-pots were placed and filled, and the servants cut themselves and each other to pieces for the vast meal to take place. But the cook-pots were far too hot, and many of the pieces leapt out from the core of the world to cool as new beings.
4- And in the space before time all were gods in that purified world. And since all were gods, some thought themselves greater than all else, and took condemnation and subjugation upon those others who did not contest them. Conflict sundered the purity of that world: those subjugated gods fell to lesser planes like scorching stars as the foundations crumbled under their feet, and those condemning gods clung to rotting, ethereal cliffsides.
5- '...Being a species of replicants brought back from literal extinction by recorded genomes of our predecessor humans, we are not technically human ourselves: more akin to children, or else an elaborate attempt for the humans to continue their lineage. It is a terrible shame that their efforts failed to come to fruition, and we must keep eternal vigil to prevent any of the offworlder abhumans to assault their holdings and contaminate their greatest and last work...'
6- We have always been on this ship: it is our light, it is our life, and the High Navigator tells that the waves have been lapping at the sides of the hull for as long as they have been aware. We are pulled by hooks and ropes from the stinking bilge and cracked out of rotten holding cases as infants, in batches of one or two, of all kinds and all places, now equal on the ship.
7- Fragmented and heretical are the words that they speak, for theirs is the language of the lesser, warped and mangled to mock the language of the greater and isolate themselves as individual beings. At their heresy they were cast into deep stone darkness, but returned with pale fire and brackish water and knowledge upon leaving the caves. Though far from enlightened, they took upon to at least preserve the greater's tongue even as they drowned and desecrated everything in their path that was not them.