International Journal of Astrobiology cambridge.org/ija Review Article Cite this article: Edwards MR (2021). Android Noahs and embryo Arks: ectogenesis in global catastrophe survival and space colonization. International Journal of Astrobiology 1–9. https://doi.org/10.1017/S147355042100001X Received: 3 November 2020 Revised: 1 January 2021 Accepted: 5 January 2021 Key words: Artificial uterus; ectogenesis; embryo cryopreservation; global catastrophes; human survival; mass extinctions; space colonization Author for correspondence: Matthew R. Edwards, E-mail: matt.edwards@utoronto.ca © The Author(s), 2021. Published by Cambridge University Press Android Noahs and embryo Arks: ectogenesis in global catastrophe survival and space colonization Matthew R. Edwards John P. Robarts Library, 6th Floor, University of Toronto, Toronto, Ontario, Canada M5S 1A5 Abstract To ensure long-term survival of humans and Earth life generally, strategies need to be in place to recolonize Earth after global catastrophes and to colonize exoplanets. In one strategy of space colonization, the physical barriers erected by time and space are circumvented by send- ing cryopreserved human and animal embryos to exoplanets rather than adult crews. There the embryos would be developed to neonates in artificial uterus (AU) systems. A similar strat- egy could also be used to repopulate Earth after human extinction events. In this paper, we review the status and future prospects of these embryonic survival strategies. A critical require- ment in each scenario is an AU system for complete ectogenesis, i.e. complete development of embryosto neonates outside the natural womb. While such systems do not yet exist, they may soon be developed to afford clinical assistance to infertile women and reproductive choices to prospective parents. In human survival schemes, AU systems would likely first be used to extend conventional survival missions (e.g. subterranean bunkers) by replacing some adult crew members with cryopreserved embryos. For major mass extinctions and all far future events, adult crews would be entirely replaced by embryos and androids. The most advanced missions would feature orbiting embryo spacecraft for Earth recolonization and analogous interstellar spacecraft for colonizing exoplanets. We conclude that an advanced civilization using such an integrated, embryonic approach could eventually colonize distant parts of its home galaxy and potentially the wider universe. Introduction In the last few decades, there has been increasing recognition that the future of our civilization on Earth could be bleak. Global warming is the immediate threat, together with its subthemes of sea-level rise, pestilence, famine and conflict. Yet there are many other ways our civilization could fail, from declining fertility rates to pandemics to replacement of humans by AI to sim- ple urban decay (Baum, 2015; Avin et al., 2018; Turchin and Denkenberger, 2018). While these threats individually might not be so severe as to cause human extinction, collectively they might conceivably do so (Kareiva and Carranza, 2018). Other events could on their own have a magnitude sufficiently high as to cause human extinction. Asteroid collisions could potentially destroy much or all of the biosphere and render the Earth uninhabitable for many years (Walkden and Parker, 2008). Other potential mass extinction events include solar processes (e.g. coronal mass ejections) and supervolcanoes (Denkenberger and Blair, 2018). The remaining classes of mass extinction events, chiefly of geological origin, have taken place frequently in the last 250 million years and are thus nearly certain to occur in the future as well. They include glaciation periods, including those of the ongoing Quaternary glaciation, and periods of episodic volcanism, which gave rise to at least four of the last five major mass extinctions (Wignall, 2005; Ward, 2007; Feulner, 2009). Finally, the steadily increasing luminosity of the sun will guarantee an end to life on Earth in a few billion years (Klee, 2017). These multitudinous risk factors, especially the human-caused ones, have led to renewed proposals to safeguard civilization. The proposals include securing human populations in sub- terranean caverns; in giant ships orbiting the Earth; in lunar or Martian colonies; or, in the extreme case, on exoplanets. Subterranean bunkers remain a viable option for extinction events with low magnitudes and lasting not more than a few decades (Jebari, 2015), but not for a longer duration or higher magnitude events. Orbiting survival missions (e.g. Asgardia) have serious technical problems (Harby, 2018), while missions to terraform Mars lack theoretical viability (Jakosky and Edwards, 2018). At the extreme end, proposals for manned missions to exoplanets face such serious physical and biological constraints as to be entirely unrealistic (Klee, 2017). There is, however, one lesser known strategy for colonizing other worlds which could not only potentially circumvent these constraints, but also serve as a template for survival missions https://www.cambridge.org/core/terms. https://doi.org/10.1017/S147355042100001X Downloaded from https://www.cambridge.org/core. IP address: 207.241.225.241, on 10 Feb 2021 at 10:16:25, subject to the Cambridge Core terms of use, available at