The following essay is being published in conjunction with the “(In)hospitable Space Conference” which explores the human dimensions of space exploration and is cosponsored between the English Department of Carnegie Mellon University, the Society for Social and Conceptual Issues in Astrobiology, and the European Astrobiology Institute.
In 2030 NASA is scheduled to wrap up three decades of exploring life in low Earth orbit (LEO) on the International Space Station (ISS) and turn its attention to long duration, deep space missions to the Moon and Mars. We find ourselves, in other words, at an inflection point in space exploration. A turning point which requires us to have difficult conversations about the health and safety of the brave human beings who will be asked to travel and live for long periods in deep space. In his newest book Becoming Martian: How Living in Space Will Change Our Bodies and Minds,Dr. Scott Solomon leverages his expertise in evolutionary biology and science communication to provide a fascinating, accessible, and wide-ranging exploration of pressing questions about the physiological consequences for the humans that will be involved in deep space exploration and settlement. What is most novel about his work is that he pays particular attention to genetics and the possible evolutionary future for humans in extraterrestrial environments.
The possibility of human habitation on Mars is the central focus of the book because the red planet is the nearest, most feasible place in the solar system for us to settle. Feasible, as Solmon points out, is a relative term. Drawing on the latest planetary science, he details the challenges of living on Mars. With an average temperature of -80 degrees, an oxygen starved atmosphere, and low atmospheric pressure, humans living on our planetary neighbor would be confined to temperature-controlled, mechanically-oxygenated, and pressurized habitats and space suits. Worse yet, without Earth’s protective magnetic field astronauts on Mars’s surface would receive in one day the equivalent of two years’ worth of radiation on Earth. At levels this high, settlers would have to live in underground habitats and limit the time they spent on the surface to avoid significantly increasing their risk of cancer and other dangerous conditions. Solomon also points out that food would be an issue. Though movies like The Martian depict farming the red regolith of Mars, he reminds readers that it, and any water drawn from the planet for agriculture, contain perchlorates which would poison most edible plants or make plants immune to the poison inedible for humans.
By describing the myriad physical challenges of Mars, Solomon sets the stage for a detailed discussionof how these conditions are likely to affect the human body and what the long-term evolutionary consequences might be. In Chapter 3 “Space Medicine,” Solomon teaches readers what medical researchers have learned about the physiological risks of space from decades of studying animals and astronauts. One risk that receives a lot of attention is the long-term exposure to microgravity. Spaceships with artificial gravity, though theoretically possible, are still science fiction. As a result, astronauts headed to Mars will be making the months-long trip in microgravity. Though floating freely in space is a novel experience and gets a lot of screen time, what garners less attention is the invisible toll that it takes on the human body after weeks and months. Solomon recounts the variety of physiological systems that are affected: muscles, including the heart, atrophy; bones weaken; fluids shift; body biomes change; the optic nerves in the eyes swell; etc. The good news is that most of these conditions are usually temporary. When astronauts return to Earth, after a few weeks or months fluids readjust, muscles and bones restrengthen, and biomes rebound. But what happens to humans that stay permanently on Mars?
Becoming Martian is most interesting when it contemplates the physiological risks and changes to human bodies that live perpetually on Mars or are born there. After all, any dream of humans and human civilization spreading beyond Earth and evolving can only be realized if humans can thrive and reproduce in extraterrestrial environments. Because no human has lived in deep space (i.e. outside of the Earth’s protective magnetic field) for more than a few weeks or been born off-Earth, we don’t currently have a robust understanding of what the effects of living long-term or reproducing on Mars, or the Moon, would be. To explore the possibilities, Solomon takes readers behind the scenes at Brookhaven National Laboratory where researchers are experimenting with rodents to extrapolate what might happen to humans exposed to regular low doses of cosmic galactic radiation. He also reviews past experiments with fish and rodents to consider what is currently known about the effects of microgravity on complex organisms in utero and whether they can reproduce in microgravity. The discussion of human reproduction he offers, though theoretical, is nonetheless thoughtfully grounded in the currently available space medicine research. Given what we know about human bodies in space, Dr. Solomon suggests that fetuses gestating on Mars may develop physiologically in ways which complicate the process of natural birth and may pose risks to their mothers whose bones will be substantially weakened by living in a low gravity environment. Further, weaker bones and muscles, especially the heart, make it unlikely that Martian offspring would be able to survive a return trip to Earth whose gravity would be two and a half times stronger. Further, children born on Mars would live in a more microbially impoverished environment making them more susceptible to Earth’s abundant pathogens.
Because moving between worlds will be physiologically challenging, Solomon predicts that once Mars has a self-supporting native population it will likely need to remain separate and develop on its own evolutionary trajectory. Natural selection, from an anthropocentric vantage point, however, is a cruel process. Maladapted organisms perish or suffer. No individuals in the history of human evolution are likely to be more poorly adapted to their environment than the initial generations living on Mars. Countless mothers and offspring will die in childbirth. Increased radiation levels will raise the risks of mutations resulting in cancer, cognitive impairment, cardiovascular disease, immune system suppression, etc. Though Homo martianus could be left to suffer the slings and arrows of natural selection until they developed the necessary adaptations to maintain population stability, Solomon explores the possibility of an alternative route. Animated by the work of geneticist Chris Mason, Chapter 8 “Next Humans” examines the question, “What if we could accelerate the process of adaptation and minimize the human suffering that it would otherwise entail?” In the chapter, the author offers an accessible history of the modern science of gene editing. With the aid of advanced techniques like CRISPR, he imagines a possible future in which RNA sequences snipped from the genomes of hardy organisms like tardigrades might protect Martian adults and children from the ravages of radiation. He also envisions a future in which scientists might fashion designer chromosomes to help humans permanently living on Mars avoid the severest consequences of selection.
Would all of this messing around with the human genome be ethical? Solomon is acutely aware of the moral issues involved with artificial selection, particularly the dark history of eugenics, and takes pains to address them. He points to recent international efforts by geneticists to address the morality of gene line editing as evidence that we have learned from our past mistakes and are taking careful measures to create a more ethical future. He also reminds readers of the cruelty of natural selection. Without genetic interventions, sending people to live on Mars would be a death sentence. Finally, he asks “How far are we willing to go to ensure that in the future there will be human lives to protect?” If humans cannot adapt to living off Earth, then the whole human species will go the way of the dinosaur when the next mega-meteor hits or the sun eventually swallows the Earth in a few billion years. If genetic workarounds which allow us to adapt to extraterrestrial environments are the only way to survive as a species, then, Solomon argues, they are worth considering.
Though Solomon believes that humans will have to evolve into a multi-planetary species to survive future catastrophes, he doesn’t believe, as some colonial enthusiasts like Elon Musk or Robert Zubrin do, that we need to be in a hurry to leave Earth. For starters there are too many unknowns. As the book reveals, we don’t know whether humans can reproduce off Earth or whether fetuses can survive. We don’t have a robust understanding of what happens genetically and physiologically to human bodies exposed permanently to the harsh environments of deep space. We don’t yet have the scientific capabilities to address genetically all of the risks that living permanently on Mars would introduce. There are also some serious socio-political problems that require attention. In particular, Solomon wonders whether our tribalistic tendencies could be sufficiently managed to coexist harmoniously with another species of human or whether our differences would be the basis for competition and conflict. Given our current track record on Earth the author concludes, “I don’t think we’re ready to leave yet.”
Becoming Martian is an interesting and accessible exploration of the current state of knowledge on the challenges space poses to human health and reproduction. Solomon teaches readers about what scientists know using historical narratives and enlivens the science with anecdotes of the places and people he has visited on his intellectual journey to write the book. With his expertise in evolutionary biology, he also draws our attention to questions and research that have heretofore been underexamined by popular works on human space travel. Questions like “Can humans reproduce off Earth?” “What sort of physiological changes will permanent Mars dwellers experience?” and “How might these changes influence the traits passed on to their offspring?” are critical to any vision of an extraterrestrial future and yet have received short shrift until this book. While readers may rightfully balk at the idea of a planned evolutionary divergence, the author provides an interesting thought experiment for considering why the development of Homo martianus might serve humanity’s long-term interests as the first step in a long evolutionary journey to the stars.
