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 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 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.

4 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”)


  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.


  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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