Via Reactor:

The Fermi Paradox asks, “Where is everybody?” Even with modest propulsion, a technological civilization could spread across much of the galaxy in a geological instant, yet we see no evidence that this has occurred.

One proposed solution, Geoffrey Landis’s “percolation model,” emphasizes the geometry and probability of settlement spreading through a network of stars. Each colony has some probability of founding additional colonies, and spacecraft have a limited effective range. Below a critical propagation probability, colonized systems form finite clusters rather than a galaxy-spanning network. Expansion therefore leaves persistent voids, potentially including our region. Cultural divergence and declining expansionist motivation could further increase this unevenness.

This essay proposes a biological mechanism that might lower the probability of successful propagation. If each colony is founded by a subset of the population of its parent colony, genetic diversity may decline at each successive step. After several iterations, distant colonies could become sufficiently homogeneous that reduced genetic resilience would leave them vulnerable to environmental catastrophe or disease. Repeated local extinctions could further reduce the species’ total genetic diversity, producing a self-limiting cycle of expansion and collapse. Large regions of the galaxy might therefore remain uncolonized, and our apparent isolation could reflect our location within one such void.

The hypothesis faces substantial objections. Reduced genetic diversity does not necessarily entail a proportionate loss of fitness or resilience. Founding populations could be selected specifically to preserve diversity, while cryopreserved gametes, embryos, genetic material, or digital genome sequences could carry far more variation than the living crew alone (as in Nolan’s Interstellar, for example). This assumes, moreover, that extraterrestrial reproduction depends on genetic mechanisms broadly analogous to ours. Expansion might also proceed in parallel rather than as a single serial chain, allowing multiple lineages to preserve or recombine diversity. Sufficiently advanced biotechnology may largely decouple an interstellar civilization from the reproductive bottlenecks that constrain the dispersal of terrestrial species upon which this essay is based.