Mars Evolution (Script) (Patreon)

It’s fun to think about humanity settling the galaxy. Outposts of familiar homo sapiens spread among the stars. But there may be nothing familiar at all about these distant, future spacefarers. Human populations on other planets may quickly evolve into things that look nothing like humans as we know them. And it will start with Mars.

We may or may not ever become an interstellar species. It’s likely, however, that we’ll at least take a shot at becoming interplanetary. Unless we manage to self-destruct in the next little while, humans will be around for a long time.  At some point, perhaps soon, perhaps in the far future, we will try to colonize Mars. That colony will face monumental challenges to its survival. But if those challenges are met, then we may reach a time when many generations of humans have lived and died on the red planet. Those people will be very different to us. How will they change? Will Martian humans, or human Martians, evolve? Will they eventually become a species distinct from homo sapiens? 

Humans have never stopped evolving. Whenever a human population is isolated, characteristic genotypes develop. Sets of genes defining skin pigmentation, height and build, immunities, even facial structure define the group. The more isolated the population, and the more extreme the environment, the quicker this adaptation happens. For example humans of Tibet developed genetically-coded larger lung capacities, faster breathing, and higher haemoglobin production. These traits developed soon after they moved from neighboring China to the high altitude Himalayas around 3,000 years ago. Mars is quite a bit more isolated and extreme than the Himalayas. How might we adapt there?

First, let’s think about this evolution thing. It’s important to remember that evolution doesn’t just morph a species into the optimal form for its environment. Evolution is blind. It’s an emergent effect of mutation and natural selection. Mutations occur at a steady rate due to DNA copying errors and through chemical and radiation damage. Mutations that improve the function of a gene or add a new useful trait will be more likely to spread through a population. Those that reduce function get weeded out. But natural selection also maintains what traits we have. If a genetic trait is no longer useful then random mutations will gradually destroy it. Like sight and pigmentation for cave fish, or prehensile tails and appendixes for humans. Use it or lose it.

So what traits are likely to be enhanced or developed on Mars? And which are likely to decay? Mars is very different to Earth, but the differences that we adapt to will depend enormously on to what degree our technology addresses those differences. Let’s start with the one that’s hardest to fix.

Low gravity. Mars has a surface gravity 38% that of Earth. This could have different effects. Lower gravity requires less bone and muscle strength to function normally. Strength may not be as strongly selected for as on Earth. Perhaps over the generations Martian humans would become intrinsically weaker. But there’s another effect to consider. We know that the zero-g experienced in orbital or interplanetary space leads to decreased bone density and muscle mass in astronauts. We’d see this in the first Martian colonists also. Over the years of a human life on Mars this could be a huge health issue, so genetic adaptations that countered the risks may be very strongly selected for. 

Perhaps the initial selection will be for people with especially strong bones and high muscle mass. People who can afford a little strength loss and still be healthy. This is an especially compelling scenario when you consider that bone strength makes us more resistant to injury. A really important issue may be childbirth. A mother’s pelvis needs to be able to withstand significant pressure that has nothing to do with the gravitational field. Extremely brittle bones may greatly increase both infant and maternal mortality. That would be a huge selection pressure in any population without very consistent access to safe c-sections. So will martians become stockier or skinnier? Over time people are likely to develop a resistance to low-g wasting, after which strength may go down. But until then we may expect strong selection for very robust individuals.

That same low gravity may also affect height. It takes a lot of effort for our hearts to pump blood from our feet to our heads. That’s why lying down feels so good. In low-g the heart doesn’t have to work so hard so it’s less of a disadvantage to be very tall. In fact, it may be a real advantage. After long zero-g missions, astronauts lose significant muscle mass in their hearts. A life on low-g Mars could be a serious risk for early cardiac problems. Having a little extra height would keep the heart more active and healthy. Perhaps Martian humans will end up much taller than their Earthling forebears.

OK, gravity isn’t the only difference between Mars and Earth. What about this pesky lack of a decent atmosphere? Well, that’s not something we can easily evolve to deal with. We’ll always need some degree of technology, both for a survivable air pressure and oxygen levels, and to protect us from space radiation. But if these technologies aren’t perfect or consistent, we may see some adaptation. This is especially true if we eventually terraform Mars, because probably whatever atmosphere we build won’t be as thick as Earth’s. There are many potential adaptations to low oxygen environments. Different mutations have arisen in Tibet versus the Chilean Andes versus the Ethiopian highlands. In all cases, these humans are able to sustain more activity with less oxygen. We might expect future Martians to be incredible endurance athletes. 

Mars’ thin atmosphere and lack of an ozone layer also means the surface is bombarded with hard UV radiation. It’s deadly and requires artificial protection. But again, assuming this isn’t completely mitigated with technology or  terraforming, we may see rapid evolution of darker skin pigmentation. On the other hand, the less intense sunlight at Mars compared to Earth means it’ll be harder to produce vitamin D. This factor is believed to result in the paler complexions found at high latitudes. So will Martians be dark or pale? It’ll depend on which of these effects we better handle with technology. Perhaps we’ll have lily-white Martians in underground cities and much darker Martians on the surface.

More dangerous than the UV are the high energy cosmic rays and solar particles. These bombard the surface due to the sparse atmosphere and the absence of a protective magnetic field. Unless humans stay underground or in very well-protected shelters pretty much all the time, they will see an increase in DNA damage from these. That’s going to mean increased mutation rates. The most obvious thing this will result in is a lot more cancer. Perhaps Martians will evolve defenses. We have natural DNA repair and cancer-fighting mechanisms. These may become enhanced. Most mutations are bad, but sometimes they’re beneficial. An increased mutation rate means evolution may proceed faster than it does on Earth.

The final really important issue is that Mars is sterile. As far as we know, no microbes whatsoever. The human immune system is constantly being exercised by exposure to Earth’s biosphere, which contains countless bugs bacteria and viruses. This results in a massive selection pressure to keep our immune system up to date. In an environment absent those pathogens, the genes that code for immunity will graduallyte mutate into uselessness. Use it or lose it. Future Martians will be highly susceptible to Earthly diseases. And this effect may actually speed up their divergence from the humans of Earth.

See, even if Martian colonies are extremely well resourced and have technologies to mitigate a lot of the challenges of Mars, there will be an inevitable drift between the Martian and Earth populations. When populations of the same animal species are isolated from each other they drift apart genetically. At first it’s just cosmetic, but eventually there’s a drift in function and, ultimately in their capacity to breed together. At that point we consider the populations to be separate species. Speciation has occurred. This effect will be amplified on Mars because the intermixing with Earth populations will be minimal. Earth will quickly become a deadly place for Martians. They’ll find Earth’s nearly 3-times-higher gravity incredibly uncomfortable, and any stray viral or bacterial infection could kill them. This latter will make them very wary about allowing Earthling visitors to Mars.

And this feeling of separation may lead Martians to thoroughly embrace genetic manipulation technology. Why wait for evolution? It will probably be possible to edit entire genomes of adult organisms at that point. Future Martians may very actively take their evolution into their own hands. 

The inevitable divergence between Earth and Mars will eventually lead to speciation. But that’s a very slow process. Homo sapiens haves been around for 200,000 years in some pretty wildly different environments. This has led to an incredible variety of physical appearance. Yet we’re all still homo sapiens. Our cousins, homo-neanderthalensis, homo-erectus, homo-floresiensis and others evolved – speciated – from a common ancestor, and they shared the Earth with us for millennia. They’ve since gone extinct, leaving us as the only species of the genus homo. But perhaps a new species of human is ahead. Give Martian colonies several tens of thousands of years and some rapid evolution and homo-Martiensis may enter the scene. Tall, strong-boned yet slender, enduring yet disease-prone, and cosmetically very distinct. Perhaps they’ll be the first in a long line of descendent species that spread their way, planet-to-planet, then star-to-star, across the reaches of space-time.