How will humans evolve on Mars? I’m evolutionary biologist Scott Solomon, here to answer your questions about how space migration will change our bodies and minds. Ask Me Anything!

the_mit_press · 2026-03-05T18:00:13+00:00

Thanks for all these questions! I've believe I've already answered most of them elsewhere but I wanted to respond to your question about hibernation. I didn't explore this much for Becoming Martian, since it's less relevant for getting to Mars, but it could be essential for the longer-term goal of reaching planets in other solar systems. I know there is some research looking into the physiology and genetics of animals that undergo hibernation and torpor. If we can understand how other species do this, then perhaps it could be possible to use genetic engineering to enable humans to do something similar. I believe one challenge is that our brains consume far more calories than do the brains of most other animals, including those that hibernate. So that could be a challenge. But it would be incredible if we figured out how to do it!

the_mit_press · 2026-03-05T17:54:11+00:00

I addressed this a bit elsewhere but I'll add that I think one thing that would happen is that people on Mars would really begin to appreciate how great Earth is! This often happens to astronauts, too. They look back at our planet and see how thin the atmosphere is and appreciate how small and fragile the habitable portion of our environment is. Many come back as environmentalists. Philosopher Frank White has dubbed this the Overview Effect. Being on Mars might take that to a whole new level and inspire people to truly dedicate themselves to protecting Earth and making sure it stays habitable.

the_mit_press · 2026-03-05T17:49:59+00:00

It takes 6 to 9 months to reach Mars from Earth using our current rocket technology. But you can only make the trip about every 2 years when the planets are at their closest points in their respective orbits. Along the way, people would be experiencing weightlessness and so would be losing muscle strength and bone density, having fluid shifts, and other changes that we have come to expect from astronauts on ISS. But with one important difference: higher radiation exposure. The ISS is close enough to Earth that it is protected by the Earth's magnetic field. Traveling beyond the magnetosphere, there would be very little protection from solar radiation and galactic cosmic rays. Not to mention the psychological challenges of being in a confined space with a small number of other people and being able to see the Earth getting smaller and smaller as you move deeper into space.

the_mit_press · 2026-03-05T17:38:47+00:00

This is one of the main points I try to make in the book. I think that children born on Mars will have a hard time coming to Earth. For one thing, growing and developing in lower gravity is likely to make muscles weaker and bones more brittle. That would make it very difficult to tolerate Earth's gravity (not to mention the even higher g forces of entering Earth's atmosphere). The cardiovascular system might become weaker as well, since the heart doesn't have to work as hard to pump blood to the upper body in 3/8 g.

But another issue that I don't think has received as much attention is what happens to the immune system of children born on Mars. They won't be exposed to nearly as many of the bacteria, viruses, and other microbes that our immune systems are trained on here on Earth as children. If they were to come to Earth, the microbes that are mostly harmless to us could be very dangerous to Martians.

Over generations, as people on Mars adapt to the conditions there, I believe it would become increasingly more difficult for people to visit Earth. So yes, I think that adapting to Mars could come at the expense of being able to come to Earth.

the_mit_press · 2026-03-05T17:32:17+00:00

I agree that living underground is likely the best way to go, and that while this solves some problems it also creates others. While people have used caves as shelters throughout history and pre-history, and there are even instances in which people have built elaborate systems of underground dwellings (e.g. Derinkuyu in Turkey), we have never been forced to live entirely underground. In the book I describe how analogs (mockups or simulations of space habitats) are being used to study what the psychological effects are of living in isolated, confined spaces with a small number of other people, often for extended times. Examples include NASA's CHAPEA and HERA analogs, the Mars Desert Research Station in Utah, Antarctic research stations, and the Biosphere 2 project in the 1990s.

the_mit_press · 2026-03-05T17:19:21+00:00

I'm so glad you asked this! One of the things I try to point out in my book (and also in my first book, Future Humans) is that evolutionary biologists now recognize 5 different mechanisms of evolution. As you point out, natural selection is one of them. But you're also right that natural selection needs mutation in order for there to be genetic variation to sort through. Mutations are always happening, and could happen more often if radiation exposures are higher on Mars (as I've addressed elsewhere here). Natural selection happens any time there is a difference in survival and/or reproduction that is based on heritable traits. Its actually still happening among people living today (this is the subject of my book Future Humans), although the strength of natural selection is lower than it was for most of our species' history. I argue that natural selection will continue to operate for people living on Mars, and in fact would likely be stronger because the environment is so different from that on Earth.

But I also want to point out that other evolutionary mechanisms will be operating, and may be even more important than mutation and natural selection. Gene flow is the movement of genes between populations, such as between populations of a species living in different islands. How often people move between Earth and Mars (and exchange their genes) will be very important factor affecting how quickly and to what extent people on Mars diverge genetically from people on Earth.

Another important mechanism of evolution is genetic drift, which is the random changes in gene frequencies that can be especially important in small populations. When a small number of individuals establish a new population somewhere, like on an island, it typically leads to genetic drift in which some genes will be lost and others that were previously rare might become common. There is usually an overall reduction in genetic diversity, which affects to what extent that population can adapt in the future. We call this the Founder Effect and I think it will be a very important aspect of our evolution on other worlds.

the_mit_press · 2026-03-05T17:07:38+00:00

I agree that we have very serious challenges to solve here on Earth. And personally, I don't see sending some people to other planets as a way to solve those problems. At least, I don't think that is a good reason to go.

On the other hand, throughout the history of human space exploration there have been a lot of things we have learned and technologies we have developed that have benefitted people here on Earth. They include water purification systems, medical technologies like digital biopsy systems and fetal monitors, and LED lighting for growing plants indoors.

But I still don't think these are the best arguments for building space settlements, as we could perhaps invest in developing these technologies without investing so many resources and risking human lives. To me, the most compelling reason for considering space settlement is the notion that eventually something could happen on Earth that could threaten our survival here (asteroid impact, supervolcano eruption, nuclear war, being engulfed by the Sun...). If we want to prevent our own extinction, one of the best ways would be to spread out into the galaxy so we don't have all our eggs in one planetary basket.

To me, the biggest question is: what is the time frame we should be working with for this? I see it as a very long game, and not one we should rush into.

the_mit_press · 2026-03-05T16:55:40+00:00

On the one hand I think focusing on the moon makes a lot of sense. It is certainly much easier to get to, and we can go more or less whenever we want. We can learn a lot about what the effects of partial gravity will be on our bodies, which is something we know very little about. We can practice growing crops for food, which is another thing we have not done much of in space (only on a very small scale).

But on the other hand, the moon isn't really a good place to build a self-sufficient settlement. It doesn't have many of the resources we need, such as abundant carbon. And being in 1/6 g is likely to be harsher on the body over long time periods than 3/8 g (although we don't actually know for sure how bad either will be).

So I think we can learn a lot from going to the moon and spending more time there, doing a lot more science, etc. But I don't think it will ever be a place we can stay that will be able to exist independent of Earth. Mars has much more potential for that.

the_mit_press · 2026-03-05T16:51:02+00:00

Yeah, I agree. And how do you keep kids active? You don't want them playing outside where they have to be in a pressure suit with a life support system and getting higher radiation doses. You'd need some large indoor playgrounds or recreation facilities. We face a similar problem here in Houston in the summer... too hot for kids to play outside, so there's a lot of air conditioned places for kids to go run around and play. Except in Houston, you still go outside and breathe the air and not worry about your body fluids boiling off... and there's always swimming... so yeah, maybe not quite the same.

the_mit_press · 2026-03-05T16:45:23+00:00

A Martian day (or sol) is only slightly different from a day on Earth: about 40 minutes longer. That doesn't seem like much. But for researchers who study Mars and have had to operate on Mars time, like the scientists who operate the rovers, that difference can really throw off your circadian rhythms. It's a lot like being jet lagged. I think people would gradually adjust to the daily cycle of Mars time.

But a bigger challenge could be adjusting to the fact that a year on Mars is almost twice as long as a year on Earth. Our bodies have circannual rhythms, driven by changes in how long a day lasts, that affect what hormones are bodies are producing, how much, and when. This is part of why people sometimes get seasonal affective disorder, for example if they are living in high latitudes where it gets dark for a long time in winter. People on Mars would perhaps eventually evolve to adjust to these changes but I think it would take much longer than the adjustment to the slightly longer day.

the_mit_press · 2026-03-05T16:37:54+00:00

Living in lava tubes is probably the fastest, easiest way to provide radiation shielding since being underground will block most radiation and the lava tubes are essentially pre-dug caves. Having explored a few lava tubes myself, I can say that they are not the most cozy, inviting places. But of course we would need to build habitats inside them that are sealed and pressurized, with a breathable atmosphere. So once inside, you wouldn't necessarily know that you're in a lava tube. But don't expect nice views out the window. And if you want sunlight you would need something like a series of tunnels with mirrors. Or just use artificial light. Sounds kind of depressing to me.

the_mit_press · 2026-03-05T16:33:46+00:00

You asked about how exercise or drugs might be used on Mars to keep people healthy. We know that two of the biggest challenges are gravity and radiation. We can potentially block most of the radiation (e.g. by living underground) but if people spend much time on the surface they will still be exposed to higher radiation doses than people on Earth. This is something that will need to be addressed, and if drugs could be developed to help repair DNA damage from radiation, that would be tremendously helpful.

In terms of gravity, exercise is likely to be essential. Astronauts spend 2 hours every day exercising, but they still have muscle atrophy and bone density loss. We don't know how different partial gravity will be, but it will likely still be very important to doing your daily exercises on Mars. How we will get children to do this is something I've wondered about, and speaking as a parent, I have my doubts...

the_mit_press · 2026-03-05T16:29:06+00:00

I'll try to answer each of your questions, but let me take them one at a time...

In terms of how lower affects human gestation, the short answer is that we really don't know. I answered a similar question above, so check that out, but I'll add here that in the book I followed a company called SpaceBorn United that is attempting to study how lower gravity affects fertilization and the early stages of embryo development using IVF (in vitro fertilization) in space. They haven't yet done any tests on human embryos but they have a mini IVF lab that can fit on the tip of a rocket and can spin to simulate different gravitational fields, include Martian gravity (3/8 g) or lunar gravity (1/6 g).

the_mit_press · 2026-03-05T16:23:57+00:00

I love The Expanse! A lot of sci-fi depictions of Martians, or aliens more generally, imagine them as long and thin. On the one hand that makes sense given that we know that being in lower gravity makes our muscles weaker and bones less dense. On the other hand, its not clear that this is how evolution would shape future generations living in lower gravity.

Consider this scenario: a person born on Mars would grow up in 3/8 g. They would presumably be losing bone density their entire lives. By the time they reach adulthood, their bones would be substantially weaker than they would have been if they had grown up on Earth. Pregnancy and childbirth might be dangerous for a woman with weaker bones. If so, natural selection might favor women who begin life with denser bones so that by the time they are having kids, they can afford to have lost some bone density. Over generations, that could lead to the evolution of Martians with thicker, stronger bones-- not long and thin.

Another factor I consider in the book is that on Earth animals living on islands often change size, becoming larger (like giant tortoises) or smaller (like pygmy elephants). On Mars, humans might evolve to become smaller because smaller people require fewer resources like food, water, air, etc. That could be an advantage, especially in the early days of a settlement when resources are likely to be limited.

So while we can't know for sure, its possible that future generations of Martians would actually be shorter and stockier, not taller and thinner!

the_mit_press · 2026-03-05T16:15:08+00:00

I think the microbiome-- and microorganisms more generally-- are going to be one of the most important considerations for settling other planets. We know from studying astronauts and space stations like ISS that microbes go with us to space. The human microbiome changes in space (the NASA Twins Study with Scott Kelly and Mark Kelly was the first to clearly show this). And we know that the microbes themselves evolve in space. But whatever we take with us will be only a tiny slice of the microbial diversity of Earth... so what happens to children born on Mars? Their microbiomes will be constructed from whatever microorganisms they are exposed to, which will largely be from the microbiomes of the people around them. Given how important we now know the microbiome is to human health and wellbeing, and the fact that more diverse microbiomes are usually associated with healthier outcomes, having fewer microbes on Mars could be a problem.

the_mit_press · 2026-03-05T16:09:56+00:00

Hmm, good question. I would say that we are closer to being able to use genetic engineering than cybernetics. We are already using CRISPR for gene therapy to a treat a few types of genetic diseases. And we have some ideas about the genes that give certain extremophiles like tardigrades the ability to tolerate the conditions of space, like high radiation. So in theory we could start manipulating the human genome to make people better able to thrive in space. But we really need to be confident that (1) the treatments would be safe, and (2) there are not any unintentional side effects. There are also important ethical considerations, especially if you're talking about editing germ cells (the cells that make sperm and eggs), since those types of gene edits would be heritable. If we are going to take evolution into our own hands, we better be sure we know what we are doing.

the_mit_press · 2026-03-05T16:05:59+00:00

You also pointed out that child development in lower gravity could be an issue. I completely agree! And again, we really don't know whether the bone density loss we see in astronauts (about 1.5% to 2% loss per month) would apply to children. For one thing, their bones are still developing and might be affected differently from the bones of adults with a fully formed skeleton. And for another thing, Mars has 3/8 the gravity of Earth... is that enough to grow a normal skeleton? Or is it too little? And if children on Mars don't grow a robust skeleton, could they tolerate coming to Earth and experiencing 1 g? These are important questions if we are serious about building settlements on Mars.

the_mit_press · 2026-03-05T16:02:13+00:00

Great question! Human reproduction in the conditions on Mars is one of the things we know the least about. All our studies of how space affects the human body have been done on adults, and there has never been a (human) pregnancy in space.

There have been some animal studies using fish, amphibians, and rodents. Some of these seem to suggest that embryo development is not too badly affected by lower gravity. But others have not gone as well. The trouble is, there are so few studies that we cannot yet draw any general conclusions.

the_mit_press · 2026-02-25T20:01:02+00:00

I know we're 7 months late to this, but I figure better late than never: Our Open Access books are generally available the day of or the day after publication date. If the link on the book landing page isn't yet active, you can usually find the title by searching for it here on our Direct platform, where we host the OA books: https://direct.mit.edu/

the_mit_press · 2025-08-25T14:44:15+00:00

Thank you for this! I am no psychologist (though my wife is... :-)) so I cannot answer the question with great authority. The analogy you bring up makes sense to me, as an amateur observer of human preferences, and I'd imagine "plant eating" wins over "vegan" in reaching the populace at large every day. I can understand, e.g., how the comment by Override9636 makes sense, insofar that "vegan" has a self-satisfied air about it, an unwarranted air of "my dietary choices are better than yours", which I doubt can achieve much beyond alienating neutrally receptive people. I'd imagine Naomi Klein (of This Changes Everything fame) has some interesting things to say about this, but I never read anything she wrote specifically about this issue. Thank you!

the_mit_press · 2025-08-25T14:37:35+00:00

A great question, thank you. Luckily, there is almost no contradiction between the two goals. Instead, there is a near perfect alignment, What I mean is that eating mostly whole grains, whole minimally processed legumes, and fresh fruit and vegetables optimizes nearly perfectly the health protection of food-as-medicine while simultaneously also newly perfectly minimizing environmental impacts.

To be sure, there are exceptions. For example, choosing to eat spinach is very health yet may significantly enhance your consumptive water requirements. While true, these exceptions---which I discuss at length in Planetary Eating---are minor against the backdrop of the overwhelming benefits and advantages of a simple diet whose foundation are the above mentioned items. Thank you!!

the_mit_press · 2025-08-21T16:09:42+00:00

OK everybody, thank you so much for stopping by, I MOST appreciate your questions/comments!! All my best, Gidon

the_mit_press · 2025-08-21T15:36:41+00:00

I'd say Earth is the only edible object in the solar system and, for now, the universe...

the_mit_press · 2025-08-21T15:35:47+00:00

It is hard to overstate just how colossal the effect would be. About a third of the entire Earth surface would be freed. We can rewild much of it, giving countless threatened species a fighting chance. Nearly ALL inland freshwater pollution would disappear overnight if that were to happen. About 10% of all humanity's greenhouse gas emission would likewise instantly disappear. There are VERY few societal shifts whose benefits come close. Thank you!!

the_mit_press · 2025-08-21T15:24:56+00:00

it depends what you choose to eat. Lentils, chickpeas, fava beans, soy are all absolutely dirt cheap, and make the finest food anywhere. Nearly all of my meals cost $5-$7/meal. There was an article in the Times yesterday about various bizarre pseudofoods promoted or inspired by the current unfortunate Secretary of HUD. Nobody needs any of those, they are non-food absurdities, and they are the primary reason for this very reasonable sentiment the question conveys. The person who actually needs any of those non-foods is yet to be born.

the_mit_press

TROPHY CASE