Let’s breed space humans

Part of my series on countering misconceptions in space journalism.

Image result for mars family space

Space development advocates routinely envision cities in space or on other planets, which implies the eventual existence of humans born off the Earth. For some reason this topic is surprisingly divisive, so I feel compelled to add my voice to the noise.

The concern is that humans may be unable to reproduce in a weightless, or reduced gravity environment. For example, the surface of the Moon is 1/6 g, while Mars is about 3/8 g. Both are a lot of fun if you can get time in a vomit comet!

For me, this concern doesn’t make it onto my list of short term worries, because babies are the least effective way to get humans where you need them. Space stations, Moon bases and Mars cities will need lots of highly trained humans to do all kinds of complicated work, and will suffer a terrible labor shortage. Humans below a certain age are enormous net consumers of labor, so reproduction will be a niche issue at best. In any case, it won’t be on the critical path.

This isn’t that crazy to say. We routinely deploy professional specialists across the world when we need people to operate submarines, oil rigs, or Antarctic stations. No-one ever suggested that the key to operating a mine efficiently is to produce the workers on site, with a 20 year operational delay. And since the automation of factories and mines, children have generally been discouraged from working in these environments. Indeed, migration, or human importation, has driven population growth in many countries, such as my native Australia, for the entirety of their modern existence.

So, in the short term, whether or not humans can breed in space is not really a critical problem. But what about the long term? Earth can produce plenty of humans for the Moon or Mars, but what about interstellar voyages? What about after industrial self sufficiency and post-scarcity luxury space communism is achieved? All these things may occur way before evolutionary changes could significantly alter our genome.

The second reason I’m fundamentally unconcerned by this question is that, as of 2020, we simply have no evidence at all, one way or the other, of fertility in reduced gravity. Some space station experiments have suggested problems with zero g, but not conclusively.

We know that tiny environmental changes (or nothing at all) can end the viability of a fetus. On the other hand, all aquatic species live and reproduce in an environment of neutral buoyancy. Babies are conceived and grow in a watery environment with plenty of external forces, bumps, and bounces, but no overarching orientation. An expecting mother can perform yoga, take sea voyages, swim, or lie down without the baby being harmed in any way. Personally, I think we’ll find that conception and gestation work fine in Mars or Moon gravity. Interestingly, there are animal experiments on the ISS that may eventually inform this question.

But let’s say that it turns out that humans are 100% infertile in any environment except one g, and that this has become a big problem for parents wanting children on Mars or the Moon. There is a mechanically easy fix. A maternity hotel built as a centrifuge with a truncated inverted cone floor plan can readily reproduce 1 g, or any other desired apparent gravitational force. There’s no reason why this futuristic form of maternal confinement should be cramped – any civilization capable of building a city big enough to have encountered this problem will easily have the resources to build an enormous rotating hab with generous interior spaces. Space radiation similarly.

Technologically, it’s on the level of an advanced theme park ride. Compared to replicating the industrial stack on a barren world, it’s a very nice problem to have.

13 thoughts on “Let’s breed space humans

  1. Dr. Handmer, for the short term, you are absolutely correct. People will be in space for only limited durations as you describe. But in the long term, when it becomes expected that one will live one’s entire life in space, human nature being what it is, there will be demands for having and raising children there.

    My concern is not fertility. I’m pretty sure that will not be a problem. In fact, I would imagine that third trimester, low or micro g will be a boon. But it is the growing child that concerns me. We already know that such environments have effects on bone and muscle health for adults that grew up in 1 g. We know from animal experiments that high g environments cause an organism to develop even stronger. Many have interpolated this to suggest that a low g environment will mean that children who grow up in them will be weaker, with thinner bones, and likely be cripples if they attempted to move to Earth’s 1 g.

    Your solution could be implemented, but would have to become the norm for families w/ children their entire childhood years. The other solution would be intermittent, twice daily or more, exposure to progressively higher g (g > 1) as toddlers through young adulthood, possibly combined with anabolic and bone growth meds. A visit to the “weight room” would have an entirely different connotation. That room may be where they spend their play time in active games and athletics.

    Interesting that you should mention interstellar travel. Perhaps off topic, but I don’t see such ever being feasible save for seed ships… and then there are all kinds of issues with jump starting a viable ecosystem and human culture at the end of the journey. It was this very problem that got me to thinking and then writing SciFi stories about it.

    Seaby Brown
    (Author of “All The Stars Are Suns”)

    Liked by 1 person

  2. Pregnant women can swim, lie down, etc, but they still are living under gravity. There are effects we see under zero gravity that, to the best of my knowledge, we don’t see under conditions of prolonged bed rest, like the vision loss problems. To the best of my knowledge, no mammal species has demonstrated full reproduction from conception to birth in zero g, even in conditions where we would have expected them to.

    As I understand it, even healthy astronauts who exercise every day still experience significantly weakened musculoskeletal and immune systems during stays in zero g. Their cuts apparently don’t heal, or heal extremely slowly. The experience of pregnancy and childbirth may not be survivable under those conditions. And that effect may be present in low g as well.

    After birth, the kid has to spend 20 years growing and developing. And there is definitely good reason to think that growth process won’t happen correctly in zero or low g, because it likely depends on loading on the skeleton. There’s basically nothing that’s been more constant in the evolutionary history of life on Earth than Earth’s gravity level.

    The reason people are worrying about the kid issue is because there’s basically no reason to send more people to Mars or space in general than are required to staff a scientific base. There’s nothing worth mining or manufacturing there. So the only reason to make this enormously expensive effort to build up self-sufficient cities on Mars is for the sake of colonizing it, and nobody is going to spend the trillions involved if they don’t even know if colonizing Mars is even possible with human physiology (they wouldn’t spend it anyway, but…). And it’s unlikely that anyone will find out anytime soon, because in the near-term attempting a pregnancy in low g and then raising the child there would be extremely unethical and in all likelihood illegal. So for the reproduction issue (among many others) Mars colonization is a non-starter for the foreseeable future.

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  3. I think planets are a crummy place to live, unless you happen to have evolved there. Their hold on the popular imagination is more than enough to offset the disadvantages, if it turns out that 3/8 g is adequate. But if human physiology turns out to require closer to 1 g, I think that would be reason enough to switch to asteroids. Why build a gigantic turntable on a planetary surface, when you can just have a rotating structure in space?

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  4. Casey, you clearly wrote this blog from the perspective of whether “growing” humans on site is a feasible way to get the population necessary to staff and operate a large, self-sufficient settlement on Mars. And clearly it is not. But the comments show people are as concerned about the physiological viability of raising humans in reduced gravity as they are about how to get a labor supply. It is an important issue because there will be children on Mars unless we send only one sex there. How, and how well and safely and healthy, we raise them is of utmost concern, of course. Your blog posts help us understand what it will take for a Mars settlement to be self-sufficient by focusing (realistically and mainly) on the “industrial stack”, how to get what we need to produce everything we need on Mars. But the point of having a self-sufficient settlement on Mars is to have a multi-planetary society/species, and that means, at its most fundamental, the ability to raise children and continually recreate, even reinvent, that society over generations.

    I don’t agree that for the “foreseeable future” the difficulty of raising kids will inhibit or prevent Mars settlement from advancing beyond scientific outpost size, nor do I believe we should (can) just live in free-space habitats. Therefore we have to address child conception and rearing. I think it would be best to include child rearing in the calculations of developing that “industrial stack”, at least to the degree that it has effects on achieving self-sufficiency. We may need to include highly specialized (and paid) category of labor for this purpose; we may need to consider regulations on the number and frequency of offspring, or seriously discourage it before a certain threshold of development is reached; certainly appropriate spaces should be included in development budgets.

    “Growing” humans in place to create a labor supply is silly and inefficient, but new little humans will appear and will have to be considered.


    1. I don’t necessary agree that proliferation is inevitable. Antarctic bases are all gender and yet noone has had a child there.

      I can understand that people might be concerned about viability of pregnancy and labor in space. Similar concerns existed in the past for boats, planes, and Australia. In this regard, my argument is that we have no evidence that it will be problematic, and if it is due to gravity, building centrifuges is easy compared to building an entire industrial stack.


      1. There have been at least 11 children born on Antarctic bases (or, technically, Antarctic colonies of Argentina and Chile). https://en.wikipedia.org/wiki/Demographics_of_Antarctica

        I think we’re going to want to solve this problem earlier than later as the reason people will want to go to Mars permanently in the first place will be similar to choosing to have children (legacy for the future, sense of immortality, bringing something amazing and new into the universe, love), and I agree it probably won’t be a major thing (and, as you say, a glorified giant merry-go-round would likely be sufficient if it is a major thing).


      2. There have even been several babies born *on* aircraft carriers to military personnel even though it’s strictly prohibited and deployments rarely even exceed 6-7 months and usually they’re close enough to land for pregnant women to be sent to a shore hospital. But some women, strange as it may sound, either do not notice the pregnancy until later (ie they’re large, maintain periods while pregnant, etc) or for whatever reason do not let themselves acknowledge it (ie were using protection and thus have no reason to suspect they might be pregnant, etc). Once we’re sending tens of thousands of people to Mars, eventually some babies will slip through. Life, uh, finds a way.


  5. Mars gravity is less of a concern to me than the nine months minimum to get there. Cosmonauts reportedly refused to produce semen samples in microgravity due to the discomfort involved. Once this becomes common knowledge, only monks will be willing to sign up for such an ascetic pilgrimage.


    1. There have been 12 month stints on ISS and Mir. But typical crewed trajectories to Mars are 6-8 months, with SpaceX planning 3-4 month transits, and that’s without hydrolox, without high Earth orbit refueling, and without nuclear thermal, all of which could enable even faster transits. 9 months is closer to the *maximum* reasonable transfer time for a crewed mission than the minimum.


  6. If you live in a rotating structure in space and the tether holding the parts together fails, the two pieces go their separate ways. That’s not good, but it’s not instantly catastrophic. If you live in a rotating city on a planetary surface, spinning fast enough to give you the extra 5/8g, and the bearings fail, everyone in the city undergoes extremely high acceleration until their velocity matches that of the surrounding planet, with the release of all the kinetic energy. In a word, bearing failure means your whole city explodes. It’s not just like an amusement-park ride.

    If it turns out that near-1-g gravity is necessary for long-term human health, I don’t think we’ll ever live in gigantic rotating structures on the surface of planets with insufficient gravity. Having it be just the residential district isn’t a big help. If we only need a few hours in a personal centrifuge every now and then, sure, that’s just one more cost of having humans on site. But if we need to live there all the time, for any significant portion of our life cycle, then we might as well focus on colonizing Venus as Mars.

    I still think asteroids are likely to be the way to go. Or rather, they would be if not for the need to have dreams pay the bills, combined with the fact that people apparently can only dream of planets. There’s less material than in planets, but far more than we’ve dug up in all of our history so far.


  7. At the same level of analysis, Starship is conceptually no more sophisticated than 1000AD fireworks. Size matters. Safety margin requirements matter. A merry-go-round doesn’t need anything specifically designed to dissipate kinetic energy, because it moves at a speed that people can crash at without significant injury.

    How big is the residential district? Let’s say a radius of one kilometer. A city that’s approaching autarky would have a residential district that’s much, much larger. But that’s about how far I walk to the grocery store. We can imagine that a city could function in chunks of that size that you have to leave and enter at the hub. Maybe. Designing these choke points into the traffic system sounds like a pain and a half. And only the edge is at the full 9.8 m/s2, so there would have to be a bunch of non-residential real estate in the interior if our biology turns out to require us to live very close to 1g, which means the residential area has to be split among more of these things. We could bring the number down by building taller, although that would mean proportionally more load on the bearings per square meter of bearing.

    A required acceleration of 6m2/s2, at a 1km radius, has the residential district moving at about 77 m/s. The first Google hit for weight of a house said about forty tons. This would be the whole shebang, streets and sewers and whatever, not just houses. On the other hand, a house isn’t designed for low mass. Call it ten tons. The coefficient of friction for a bearing, first hit have a range from.001 to .005. Let’s give an order of magnitude for free, and assume .0001. The bearings would be dissipating 280 Watts per person. They’re under a city, so there’s nowhere for the resulting heat to go, so the bearings also need 280 Watts of air conditioning. And we’ll need access tunnels for maintenance. Bearings wear out. Is steel strong enough for bearings that hold up a city? I suspect not, but I don’t know how to calculate it. What do we use, if it isn’t? I don’t know.

    My guess is that we will be just fine in .38g. But that’s just a guess. If we turn out to need the full g full-time for long-term growth and development, it’s a serious increase in the cost and complexity of the city. “It’s just like a merry-go-round” a facile analogy, not a serious solution. There are no cities on merry-go-rounds.


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