Abstract
Humanity typically imagines interstellar civilization as an extension of its present biological condition: human beings remain fundamentally unchanged while spacecraft become faster, safer, and more capable. This paper examines the inverse possibility. The principal barrier to deep-time interstellar civilization may not ultimately be the spacecraft, but the biological traveler. Human physiology is the product of terrestrial evolution and depends on environmental conditions that long-duration spaceflight must technologically reconstruct or compensate for. A sufficiently advanced technological civilization may therefore face an evolutionary choice: continue transporting a terrestrial biological environment through space, or progressively transform the beings that travel through it.
The paper develops a distinction between replacement and continuation models of post-biological transition. Under a replacement model, artificial systems outlive their biological creators. Under a continuation model, biological intelligence, artificial cognition, neural augmentation, synthetic embodiment, and perhaps substrate migration progressively converge, making the boundary between creator and creation increasingly ambiguous. This possibility raises a problem deeper than engineering: whether personal and phenomenal continuity can survive changes of substrate. A functionally perfect copy is not thereby numerically identical to the copied person, and gradual replacement does not by itself settle the metaphysics of consciousness.
The analysis then extends beyond survival to agency, value drift, boredom, civilizational plurality, and the possibility that post-biological descendants may fragment into radically different forms of mind. A structured extraterrestrial-observer thought experiment is introduced solely as an ethical instrument, not as an empirical claim. It examines non-interference, paternalism, disclosure, technological asymmetry, and the moral
obligations of a civilization possessing overwhelming power over a younger one. The paper argues that interstellar maturity cannot be reduced to propulsion. It must also concern the architecture of persistence, continuity of persons and values, and restraint in the use of power. The decisive transition toward a long-livedinterstellar civilization may therefore be not the construction of a vessel capable of carrying unchanged humans
indefinitely, but a transformation in what humanity is prepared to become - and in what it refuses to lose while becoming it.
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