Ellis et al. disambiguate impacts of exposure to extrinsic mortality, or external causes of death, on the tight-linked survival and reproductive life-history traits of humans. The authors’ appraisal and re-synthesis of findings on group and individual outcomes across human sociobiological diversity and experience deliver nontrivial conclusions about evolving life-history strategies, although without the benefit of more compelling insights on sustainable human development. Extrinsic mortality sources, such as warfare, natural disasters, community violence, infectious diseases, and food shortages, may be relatively insensitive to adaptive, actionable human decisions, rendering people largely incapable of mitigating or averting lethal effects (Abrams, Reference Abrams1993; Clark Reference Clark2019, Reference Clark2021a,b, Reference Clark2023). Effort and time allocations for lowering mortality or elevating survival can yield disproportionate bad returns on investments, so eco-evolutionary trends, including biological innovations and normative cultural policies and practices against risks, become ineffective at reasonable bioenergetic and developmental costs. High extrinsic mortality, for example, negates the value of future reproduction and supports tradeoffs favoring earlier reproduction onset, which shortens mortality exposure prior to reproductive maturity and lengthens reproductive span (Chisholm, Reference Chisholm1999; Migliano et al., Reference Migliano, Vinicius and Lahr2007; Quinlan, Reference Quinlan2010). Such straightforward contexts show occasions that improve progeny quality only weakly diminish their mortality, creating selection pressures at transgenerational scales that optimize phylogenetic, ontogenetic, and sociogenetic strategies for sexual fertility over fecundity or offspring count (Chisholm, Reference Chisholm1999; Ellis et al., Reference Ellis, Figueredo, Brumbach and Schlomer2009; Quinlan, Reference Quinlan2010). However, sensing stressful ambient conditions that contribute to extrinsic mortality also enables humans to calibrate personal choice and expression of life-history strategies within an individual’s lifespan, enriching sociobiological complexity and helping delay pubescence while accelerating both pregnancy pace and parturition or birth rate. Ellis et al. resolve these fundamental opposing processes on life-history trait expression through conceptualization of a two-tier model, which places influences of bioenergetics and ambient cues on respective bottom and top tiers. Considering both tiers together is necessary to account for observed countervailing occurrence of slower to faster life-history traits and, notably, may offer a framework to predict and foster human robustness against perilous living in extreme-Earth and extra-Earth environments, meaningful scenarios surprisingly left unexamined by the authors, particularly given widely accepted United Nations recommendations for sustainable living on Earth and in outer space (DESASD, 2015; UNOOSA, 2023a,b).

Humanity faces possible irreparable ecological, social, economic, and political troubles that intensify extrinsic mortality for Earth populations. Scholars to popular fantasists often envision future solar system exploration and colonization of space gateways or extraterrestrial locations as solutions for endangered human existence on Earth. Solutions range from mere escape to distant inhospitable/hospitable planetary refuge to establishing prosperous space-Earth circular economies that drive space-Earth sustainability (Averesch et al., Reference Averesch, Berliner, Nangle, Zezulka, Vengerova, Ho, Casale, Lehner, Snyder, Clark, Dartnell, Criddle and Arkin2023; Clark, Reference Clark2025; UNOOSA, 2023a,b). NASA’s space-democratizing Artemis program plans to land the first person of color and first female on the Moon surface from a lunar-orbit gateway on its next mission, achieve sustainable human presence on the Moon by year 2028, and further prove technologies, capabilities, and business strategies for future successful spaceflight-crewed missions to Mars and other destinations. Severe extra-Earth health and performance risks (Chapes et al., Reference Chapes, Clark, Lowe, Narayanan and Jha2022; Clark, Reference Clark2022a,Reference Clarkb; Seylani et al, Reference Seylani, Galsinh, Tasoula, Anu, Camera, Calleja-Agius, Borg, Goel, Kim, Clark, Das, Arif, Boerrigter, Coffey, Szewczyk, Mason, Manoli, Karouia, Schwertz, Beheshti and Tulodziecki2024) associated with exposure to harmful ionizing radiation, altered gravity, social isolation, physical confinement, and dietary deficiency, among other stressors, nonetheless present extrinsic mortality threats to all humans, with forecasted major changes in biology and evolution of survival and reproductive life-history strategies (Dubé et al., Reference Dubé, Santaguida, Anctil, Giaccari and Lapierre2021; Jain et al., Reference Jain, Chuva de Sousa Lopes, Benotmane, Verratti, Mitchell and Stukenborg2023; Mishra and Lauderer, Reference Mishra and Luderer2019; Ronca et al., Reference Ronca, Baker, Tamara, Bavendam, Beck, Miller, Tash and Jenkins2014; Schuster and Peck, Reference Schuster and Peck2016; Steller et al., Reference Steller, Blue, Burns, Bayuse, Antonsen, Jain, Blackwell and Jennings2020). Some female reproductive physiology and health risks from real and simulated space conditions include thromboembolism in combined oral contraceptive users, functional insufficiency of the corpus luteum, and decreased decidualization and progesterone and luteinizing hormone levels. In contrast, some male reproductive physiology and health risks under analogous constraints include sperm DNA fragmentation and lower testosterone and sex hormone-binding globulin levels, sperm motility and vitality, and male-offspring ratios. Living in space habitats during prolonged travel and settlement might additionally restrict privacy and access to intimate partners, impose hygiene and abstinence protocols, and heighten risks of interpersonal conflicts and sexual violence. Similar to the conclusions of Ellis et al., mortality-tied costs in conceiving progeny in extra-Earth environs may already reveal important natural shifts in life-history traits, including favoring births of female offspring to raise resource bounds on scarce oocyte gametes as well as to propagate female sex-chromosome resilience, despite countervailing greater incidences of life-shortening and reproductive span-shortening autoimmune and metabolic diseases caused by oxidative stress and reprogramming of dysregulated maternally inherited mitochondria.

Changes in sex-trait determinism due to bleak off-Earth habitation corroborate Earth-based findings reported by Ellis et al., implying comparatively rapid-onset adaptations over one-to-few generations following exposure to mortality sources compensate or hedge reproductive successes against the expenses of potential survival failures. However, selective advantages for natural bioenergetics- or cue-induced transitions in life-history strategies may also emerge on longer eco-evolutionary timescales in heterogeneous Earth or extra-Earth niches (Clark, Reference Clark2012a,Reference Clark and Clarkb, Reference Clark2019). The authors’ model unsatisfyingly characterizes and predicts these manifest-to-latent adaptations, which help optimize survival-reproductive tradeoffs in the presence of varying extrinsic mortality. Humans did not evolve to live in extreme-Earth or extra-Earth niches, and traumas accompanying such lifestyles imminently jeopardize the quality and length of life across human lifespans and generations. Predicting human genotypes and phenotypes for known and unknown extrinsic mortality sources becomes essential in narrowing actual and prospective human-health disparities within and between different demographic groups, promoting evolutionary-medicine imperatives and enduring Earth- and astro-Darwinian trajectories (Trevathan, Reference Trevathan2007). Whether or not personalized and public health theragnostic medicine (Clark, Reference Clark2025, in press), perhaps enlisting multimodal patient data, quantum biomedicine and computing, and Artifical Intelligence/Machine Learning-powered (AI/ML) attributional and predictive inferencing, can ultimately save humanity from catastrophic despeciation or reduced trait variation in any environment remains debated. Future sustainable human development in edge cases may require significant, likely controversial, technology-assisted accelerated human evolution, such as that involving directed gene editing, phenotype capture, and other methods unacknowledged by the authors, to advance and rescue vital life-history traits for human flourishing. Ethical design and use of technologies to overcome relative extrinsic mortality must be achieved and enforced by societal governance and norms that fine-tune safe, equitable, and diverse human sustainability on or off Earth.