Prolonged space travel takes a severe toll on the human body. Microgravity impairs muscle and bone growth, and high doses of radiation cause irreversible mutations. As we seriously consider the human species becoming space-faring, a big question stands. Even if we break free from Earth’s orbit and embark on long-duration journeys among the stars, can we adapt to the extreme environments of space? This won’t be the first time that humans have adapted to harsh environments and evolved superhuman capabilities. Not fantastical powers like laser vision or invisibility, but physiological adaptations for survival in tough conditions. For example, on the Himalayan mountains where the highest elevation is nine kilometers above sea level, an unacclimated lowland human will experience symptoms of hypoxia, commonly known as mountain sickness.
At these altitudes, the body usually produces extra red blood cells, thickening the blood and impeding its flow. But Himalayans who have lived on these mountains for thousands of years permanently evolved mechanisms to circumvent this process and maintain normal blood flow. Cases like that prove that humans can develop permanent lifesaving traits. But natural adaptation for entire human populations could take tens of thousands of years. Recent scientific advances may help us accelerate human adaptation to single generations.
To thrive as a species during space travel, we could potentially develop methods to quickly program protective abilities into ourselves. A beta version of these methods is gene therapy, which we can currently use to correct genetic diseases. Gene editing technology, which is improving rapidly, allows scientists to directly change the human genome to stop undesirable processes or make helpful substances. An example of an unwanted process is what happens when our bodies are exposed to ionizing radiation. Without an atmospheric barrier and a magnetic field like Earth’s, most planets and moons are bombarded with these dangerous subatomic particles. They can pass through nearly anything and would cause potentially cancerous DNA damage to space explorers. But what if we could turn the tables on radiation? Human skin produces a pigment called melanin that protects us from the filtered radiation on Earth.
Melanin exists in many forms across species, and some melanin-expressing fungi use the pigment to convert radiation into chemical energy. Instead of trying to shield the human body, or rapidly repair damage, we could potentially engineer humans to adopt and express these fungal, melanin-based energy-harvesting systems. They’d then convert radiation into useful energy while protecting our DNA. This sounds pretty sci-fi, but may actually be achievable with current technology. But technology isn’t the only obstacle. There are ongoing debates on the consequences and ethics of such radical alterations to our genetic fabric.
Besides radiation, variation in gravitational strength is another challenge for space travelers. Until we develop artificial gravity in a space ship or on another planet, we should assume that astronauts will spend time living in microgravity. On Earth, human bone and muscle custodial cells respond to the stress of gravity’s incessant tugging by renewing old cells in processes known as remodeling and regeneration. But in a microgravity environment like Mars, human bone and muscle cells won’t get these cues, resulting in osteoporosis and muscle atrophy.
So, how could we provide an artificial signal for cells to counteract bone and muscle loss? Again, this is speculative, but biochemically engineered microbes inside our bodies could churn out bone and muscle remodeling signaling factors. Or humans could be genetically engineered to produce more of these signals in the absence of gravity. Radiation exposure and microgravity are only two of the many challenges we will encounter in the hostile conditions of space. But if we’re ethically prepared to use them, gene editing and microbial engineering are two flexible tools that could be adapted to many scenarios. In the near future, we may decide to further develop and tune these genetic tools for the harsh realities of space living.