If humans go to Mars, what happens to evolution? - Scott Solomon

Scott Solomon discusses NASA's CHAPEA experiment, a 3D-printed Mars habitat simulation located at the Johnson Space Center in Houston. These studies, known as analogs, help researchers understand the psychological toll of living in confined spaces with limited resources and crew interactions. While they cannot replicate Mars's one-third gravity or high radiation, they provide vital data on how a crew of four can survive a full year of isolation. Solomon also mentions the Mars Desert Research Station in Utah as another key facility for testing these settlement technologies. These simulations are essential for preparing humans for the reality of being 'stuck' with a small group for extended periods.

As an evolutionary biologist, Solomon argues that long-term settlement on Mars will inevitably lead to evolutionary change through multiple generations. He illustrates this using the example of Homo floresiensis, the 'hobbit' humans found on the island of Flores in Indonesia. This species evolved to be much smaller due to restricted caloric resources, a phenomenon known as the 'Island Rule'. Interestingly, islands can also produce giants, such as giant tortoises or the Komodo dragon, showing that isolation forces radical size adjustments. This historical divergence serves as a blueprint for what might happen to humans isolated on the 'island' of Mars.

The discussion shifts to the cultural and biological impact of meeting different hominid species, which was a reality for most of human history. Solomon points out that settling Mars would be the first time humans knowingly place themselves in an environment guaranteed to cause biological divergence. Unlike extreme environments on Earth like Antarctica, Mars lacks breathable oxygen and has pressure so low that human blood would boil without protection. This unprecedented level of environmental extremity makes Martian settlement a unique event in the history of life. The speakers reflect on how our species' history of interacting with other humans like Neanderthals might repeat in a space-age context.

Space travel inflicts immediate and severe changes on the human body, primarily due to weightlessness and radiation. Muscles atrophy and bones become brittle as the body reabsorbs minerals like calcium because they are no longer being strained by gravity. Fluid redistribution leads to 'space face' (puffiness) and 'chicken legs', while the brain suffers from 'space fog' due to galactic cosmic rays. Radiation beyond Earth's magnetosphere poses a high risk of cancer and cognitive decline, which NASA manages by limiting astronaut exposure time. Solomon explains that even a six-to-nine-month journey to Mars would result in significant deconditioning before the travelers even land.

Solomon explains the discovery of the Van Allen radiation belts, which are regions of intense radiation trapped by Earth's magnetic field. While these belts protect the Earth, they represent a major hurdle for deep-space travelers who must pass through them and then survive without such protection on Mars. Upon arrival, the transition from weightlessness to Mars's one-third gravity will be physically punishing for weakened skeletons. Astronauts will likely need robotic assistance or exoskeletons to move effectively after months of bone density loss. This section emphasizes that the global effects of gravity on the circulatory and lymphatic systems cannot be easily replicated by simple gym equipment.

The challenges of long-term survival include a restricted diet of shelf-stable food and the psychological need for fresh produce, illustrated by the story of a 'contraband onion' in a Russian space station. High radiation on Mars will likely increase the mutation rate in human DNA, which acts as the raw material for evolution but also causes significant suffering and 'errors' in the short term. Solomon introduces the concept of the 'Founder Effect', where a small group of colonists creates a genetic bottleneck. This means the specific traits of the first few hundred settlers will disproportionately define the genetics of the future Martian population. This reduction in diversity can lead to rapid, often unpredictable evolutionary changes over just a few generations.

Selecting the right people for Mars is a complex task that goes beyond the 'military pilot' archetype used in early NASA missions. Solomon argues that we need a genetically and psychologically diverse group to ensure long-term population health and adaptability. In isolated environments like Antarctica, the most successful individuals are team players with high emotional intelligence rather than purely 'Type A' personalities. An interesting technical detail mentioned is the preference for odd-numbered crews to provide a natural tie-breaker in decision-making and prevent factional splits. To avoid a genetic bottleneck that leads to failure, the base of the Martian 'pyramid' must be as broad and diverse as possible.

Governing a Martian colony is complicated by the 20-minute communication delay with Earth, making direct oversight from home governments nearly impossible. Solomon suggests that Martian colonists must have their own leaders with 'skin in the game' to handle local crises and legal issues like crime. While astronauts often experience the 'Overview Effect'—a profound sense of global unity and fragility when seeing Earth from space—this may not translate to children born on Mars. Just as immigrant identities fade over generations, Martian-born humans will eventually view Mars, not Earth, as their primary home and identity. This shift in perspective will fundamentally change how Martian society interacts with its 'mother planet'.

Practical Martian settlements will likely be underground to provide natural shielding against radiation and meteorites, which bypass Mars's thin atmosphere. Living in permanent darkness or artificial light will have unknown psychological and physiological effects, potentially altering human vision and spatial awareness. Humans have an innate connection to nature, known as biophilia, and the total lack of wildlife or forests on Mars could be psychologically destructive. Solomon warns that while physical ailments are bounded, psychological instability in a closed ecosystem could have a 'domino effect' leading to catastrophe. This permanent subterranean existence would create a human experience completely unrecognizable to those living on Earth's surface.

Reproduction is perhaps the greatest unknown in space colonization, as there is almost no data on human pregnancy in low gravity. Solomon highlights the risk that a woman raised in Martian gravity might suffer a fatal pelvic fracture during childbirth due to lifelong low bone density. This could lead to a society where all births are done via C-section, which in turn removes the evolutionary constraint on baby head size. Furthermore, Martian-born children would lack the immune systems to ever visit Earth, as they would be unexposed to Earth's diverse microbes. This immunological barrier, combined with potential genetic engineering via CRISPR to alleviate suffering, creates a permanent divide between Earthlings and Martians.

The ethical implications of Mars colonization are profound, particularly regarding the rights of future generations who did not choose to be born in such a harsh environment. Solomon questions whether it is ethical to use genetic enhancement to help children survive Mars if those very changes permanently exile them from Earth. However, not going to Mars also carries the risk of total extinction if a catastrophic event hits our single-planet home. He suggests that while we must eventually become a multi-planetary species, we shouldn't rush the process until we have better biological answers. The conversation concludes with a call for more research into the life sciences to match our rapidly advancing rocket technology.

In the final segment, Solomon promotes his book 'Becoming Martian' and his podcast 'Wild World', which explore these themes of exploration and evolution. He reiterates that the path to Mars is not just a technological challenge but a biological journey that will redefine what it means to be human. The host and guest agree that the topic is endlessly fascinating and represents the next great chapter in human history. They emphasize the importance of understanding our own biology before we attempt to transplant it to another world. The episode ends with a reminder of the fragility and uniqueness of our current evolutionary state on Earth.