How Mars Exploration Could Lead to a New Human Species
The upcoming Hollywood movie The Space Between Us tells the story of a boy who is born to an American astronaut on Mars. His mother dies in childbirth, but the child survives and grows up under the care of a small colony of astronauts on the Red Planet. In the movie trailer, a dark voiceover provides the premise of the movie: “His heart just can't handle gravity; his bones are too weak. In other words, there is no turning back. This question is worth pondering: if we decide to leave Earth, will our descendants ever be able to return back?
Every year we are getting closer to Mars. NASA hopes that human feet will set foot on the Red Planet in 30 years, and Elon Musk calls the figure 10 years: at first it will be a test flight, meanwhile the ultimate goal is to create self-sufficient Martian cities. In a speech in September 2016, Musk mentioned "two main paths" that humanity can take: "One path is to stay on Earth forever, and then we will face the final extinction. The alternative is to become a space-conquering civilization and a multi-planetary species."
If we ever reach Mars, living conditions there will differ from those on Earth in all respects. Adaptation to the weaker effects of gravity, intense radiation, and the complete absence of bacterial flora will force several generations of Martian colonists to experience a series of dramatic evolutionary changes in human ancestry, comparable to the onset of upright walking and an increase in brain volume.
The first evolutionary changes can be quick and subtle. Since the group of the first humans on Mars will inevitably be limited in number - Musk has proposed sending about a hundred people aboard the spacecraft - the first Martian colonists will experience a phenomenon known as the founder effect. This phenomenon is observed each time a new place, like a volcanic island rising from the ocean floor, is colonized by newcomers. The few individuals who settle in a new place, regardless of how they got there, are unlikely to represent the majority to which they originally belonged. The smaller the sample, the less likely it is to represent the larger group it came from.
If we send a hundred colonists to Mars, the likelihood that they accurately represent all people living on Earth in terms of height, hair color, propensity for diabetes or breast cancer, ability to move ears or any other genetic factors is extremely low … Whatever traits the early colonists possessed, they would pass on to their children, and thus a growing Martian colony, even in the absence of natural selection, would become something different from the inhabitants of Earth. For example, if all the astronauts we sent to Mars were red, there would be another reason to call Mars the Red Planet.
The founder effect, of course, is not limited to Mars explorers or interplanetary travelers. It can occur in any isolated or selected population. But as a number of generations change, changes can acquire a more pronounced and specific character. In conditions where gravity is only one third of the earth's gravity, pregnancy and childbirth can be much more difficult on Mars. Researchers of embryonic development in mice have found that fertility rates in mice, whose embryos were formed under artificially created microgravity conditions, are lower than under normal gravity. Interestingly, fertilization - carried out in vitro - does not appear to be affected by the decrease in gravity, but some of the embryos obtained did not develop as well as the embryos.appearing under normal gravity. The reasons for this are not yet clear, but the results indicate that mammals, including humans, may experience more difficulties during gestation on Mars than on Earth. And this, in turn, can exert a new pressure of evolutionary selection, which is not observed on Earth.
Insufficient gravity will also result in bone loss at a rate of about 1% to 2% per month. After two or three years on Mars, settlers risk losing half of their bone mass, which is likely to affect pregnant women even more, since the body requires a lot of calcium during pregnancy. Loss of bone density makes people more prone to injury, especially hip and spine fractures. Since such injuries can have irreversible consequences on Mars, people with naturally higher bone density - which was more characteristic of our ancestors than modern humans - are more likely to survive and pass on their genes. Therefore, as a result of the change of many generations, people on Mars will end up naturally having denser bones than their predecessors, which means they will be stronger in appearance.
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Martian settlers will also have to adapt to high levels of radiation. With no magnetosphere or atmosphere to protect the planet, Mars is attacked by high-energy cosmic rays, intense ultraviolet radiation and solar particles. For 500 days on the surface of Mars, a person will receive a dose of radiation that is six times the maximum annual dose allowed by employees of the United States Department of Energy. Spacesuits or underground living quarters may provide some protection, but of course, some time will still need to be spent on the surface of Mars, growing crops, erecting buildings and the like.
Radiation damages DNA, causing a kind of mutation that leads to cancer. While radiation may mean higher rates of cancer for Martian settlers, it can also speed up evolution by generating random genetic variations, including traits that are useful in the Martian environment.
These genetic variations can be ways of protecting our bodies from radiation exposure. On Earth, our skin produces melanin, a pigment that acts as a natural sunscreen. Skin pigmentation has evolved in human populations as a balance between the risk of excess radiation, which disrupts DNA production, and the risk of insufficient radiation, which interferes with normal bone formation. Many other organisms use melanin to protect themselves from radiation, including dark-colored fungi that grow where the core of the Chernobyl nuclear reactor melted. The type of melanin that provides the human body with maximum protection from solar radiation is eumelanin, which gives the skin a dark brown or black color. People who have much more eumelanin in their skinwill be able to better tolerate extreme levels of radiation on Mars, with the result that Martians' skin will be darker than that of any human.
The rover crosses the sand dunes of Dingo Gap
On the other hand, intense radiation on Mars could contribute to the evolution of new skin pigments. Carotenoids - the orange pigments that give carrots their color - are produced by many plants and microorganisms to protect them from sunlight. Although many animals have carotenoids, most of them get them from their diet. One exception is the pea aphid, a small insect that is usually green in color, but in some cases turns red due to carotenoids that it produces itself. Genomic analysis showed that the pea aphids received the genes responsible for the production of carotenoids from one fungus, which means that in rare cases, animals can borrow equipment for the production of pigment from other organisms. The harsh conditions on Mars could increase the likelihood of such rare borrowings if the end result - say, bright orange skin - were especially beneficial.
Recent research has shown that high levels of radiation also affect the brain, altering spatial memory and risk-taking behavior in some, but not all, mice. Such violations could pose a serious threat to the success of the Martian colony. However, if the same fluctuations in radiation sensitivity that we see in rodents are found among humans on Mars, natural selection will work in favor of those less affected by radiation. Future generations will be able to develop resistance to the harmful effects of radiation on the brain, helping humans better adapt to the Martian environment and increasing their ability to further space exploration, perhaps even travel to more distant habitable planets such as Proxima b.
Then there is the microbiome - bacteria and other tiny organisms that live inside and on the surface of our bodies and have a serious effect on our body. These microbes are acquired by us throughout our lives, starting with those that we receive from our mothers when passing through the birth canal. Early childhood is an important period for the development of a healthy microbiome as children receive additional microbes from their parents, siblings, friends, and the environment. Children on Mars will not be exposed to the many different microbes we find here on Earth, and while scientists still hope to find microbial life on Mars, there is still no conclusive evidence of its existence.
People on Mars
The loss of beneficial microbes can lead to adverse physical and mental health consequences for the Martian settlers. Here on Earth, we are already seeing a decline in microbial diversity in the microbiomes of people living in urban environments, where we do our best to disinfect our bodies and surrounding objects in order to prevent the exchange of diseases. In many ways, this process is undeniably beneficial - once pervasive diseases such as smallpox have been defeated by vaccine development, and improved sanitation and the availability of antibiotics have limited the spread of other diseases to specific regions. However, an unforeseen consequence of our war on microbes was the pursuit of microorganisms beneficial to our health, including thosewhich have coexisted with us for millennia and are currently under threat of extinction.
Moving to Mars can be too much of a test for these microbes, and their complete loss will almost certainly be detrimental to humans. People with a poorly diverse microbiome are more likely to develop obesity, type 1 diabetes, and possibly other illnesses, including allergies, asthma, celiac disease, and some types of cancer. Experiments in which mice and rabbits are raised under sterile conditions without allowing them to develop any microbiome whatsoever suggest a rather bleak prospect. Their immune and nervous systems do not develop properly, and their ability to obtain nutrients from food is compromised.
The microbes that live in our gut play a vital role in digestion, so in the face of the complete loss of the microbiome, the diets of the Martian settlers must undergo changes. Scientists can design specially formulated foods that include only simple sugars, proteins, and fats that are easily digested without the help of microorganisms. On the other hand, if some beneficial microbes accompany a person to Mars, they themselves can develop with him. Due to the short generation period - some types of bacteria multiply every 30 minutes - microbes develop much faster than humans, which allows them to quickly adapt to changing conditions. They will also be affected by radiation, increasing their mutation frequency and further accelerating their evolution.
The same processes will occur with any plants or animals that we bring with us, as well as with the microbes living inside and on the surface of these species. In other words, by creating a Martian colony, we will lay the foundations for a new type of ecosystem. Arranging Mars - deliberately changing the Martian environment in order to bring its conditions closer to Earth's - can lead to the development of ecosystems that are unlike any existing on planet Earth.
The good news is, Mars probably won't have an infectious disease problem. As with the human microbiome, the only viruses, pathogenic bacteria and other pathogens on Mars are likely to be the ones we bring with us. Long interplanetary travel could become a quarantine that limits the chances of the accidental appearance of infectious diseases on Mars. Most of the infectious diseases that affect humans are the result of infections we have contracted from animals, in particular birds and mammals. Many of these, such as anthrax and rabies, are carried by domestic animals such as sheep, cattle and dogs. Others, such as Lyme disease, mainly come from wild animals. On Earth, we are constantly faced with new diseases,such as Ebola and Zika, in part because these microbes regularly infect animals and humans. On Mars, we can avoid this problem if we don't bring birds or mammals there, opting instead for a selection of insects that are less likely to carry infections that can infect humans (and require less food).
On the other hand, living outside the threat of infectious disease can lead to immune system atrophy, which risks becoming an appendix-like relic, or perhaps disappear entirely. This atrophy can be caused not only by the absence of disease: during space flights, astronauts often suffer from immunosuppression, which is largely due to the stress associated with takeoff, landing and being in a confined space, but according to some reports, microgravity also plays a role here.
Immunocompromised Martians will face life-threatening diseases if they return to Earth, and humans who come from Earth risk destroying the entire Martian colony if they bring any disease with them. The risks associated with illnesses that do not show obvious symptoms, as is usually the case with sexually transmitted infections such as HIV or chlamydia, will be especially high. Close personal contact - like sex - between Earthlings and Martians would be very risky.
Put it all together: the ban on sexual intercourse between Earthlings and Martians, the founder effect, changes in the microbiome, natural selection in the harsh conditions of the Martian environment, plus weak gravity - and it becomes clear to you: the settlement of Mars will ultimately lead to the development of a completely new human species … This is a common phenomenon in the world of animals and plants isolated on the islands - remember the famous Darwin's finches. But while speciation on islands can take thousands of years, the accelerated mutation rates on Mars and the stark contrast between living conditions on Mars and on Earth are likely to accelerate the process. In just a few hundred generations - perhaps as little as six thousand years - a new species of man could emerge.
In 1950, Ray Bradbury published a series of related short stories called The Martian Chronicles, in which he portrayed a distant future in which Mars is colonized by people who have long lost all interest in and connection to Earth. The Martians Bradbury have brown skin and yellow eyes. "Have you ever thought about - well, about whether people live on a third planet?" - asks one of the Martians. “The third planet is not habitable,” her husband replies. "Our scientists say there is too much oxygen in its atmosphere."
Bradbury's fiction may well be prophetic. If the Earth is hit by some serious disasters, the colonization of Mars in the long term may be a necessary condition for our survival. However, a strategy to preserve the human species can ultimately change us forever.
Scott Solomon is a biologist and scientific writer based in Houston. He teaches ecology, evolutionary biology and scientific communication at Rice University, where he is a professor in the Department of Biosciences. His first book Future Humans: Inside the Science of Our Continuing Evolution was published on October 25, 2016 by Yale University Press.