Issue 184 – January 2022


Zero-g Zoo: Trying to Solve Reproduction in Space

Shall we go where no one has gone before? However, if we’re to stay there, we need to think about the next generation. Which means procreation in space—an issue we know very little about so far. What do we know, and what could be the potential obstacles of reproducing in space conditions?

At least officially, no human has yet had sex in space, and NASA has had a very conservative approach toward it, firmly stating that it’s not funding any research in this vein. The ESA and DLR, at least, are currently studying sexual well-being and security in extreme environments on the Antarctic Concordia Station—but that doesn’t answer the question of sex in microgravity. Plenty of thought has been given to the topic and possible solutions devised, some of which have included elaborate harnesses, Velcro, or connectible suits.

Although it’s possible that after some initial curiosity, many people won’t be very interested in partnered sexual encounters while in microgravity (rats, usually very sexually active, were never observed mating for the whole nineteen-day duration of an early space experiment) and would prefer other ways to relieve tension and maintain their sexual health. We can probably assume that the physical act of sex is going to be one of the smaller issues with human procreation in space.

Everything else is a potential showstopper.

Microgravity and radiation are the main factors changing astronauts’ physiology in space, resulting in bone density loss, muscle atrophy, eyesight problems, DNA damage, and a whole suite of other issues that appear to go back to normal upon return to Earth for the most part—but if we decided to have children in space, those problems might prove too severe.

Reproductive tissues tend to be sensitive to radiation, and only experiments outside of Earth’s magnetosphere will let us know just how harmful interplanetary voyages would be for future parents, fetuses, and children. On the International Space Station, radiation levels are approximately a hundredfold those typical of Earth’s surface. In interplanetary space, it would be some two-to-four times more than on the ISS, based on space weather at the moment. Especially thick radiation shielding might be needed in interplanetary space to allow for safe reproduction. On planetary surfaces, we could build stations in lava tubes or cover them with thick concrete made from regolith.

As to weightlessness—rotating sections of space stations and ships would help, but those ideas remain firmly in science fiction so far. Would we need to overcome this engineering challenge or only reproduce on planets and moons? Maybe spacefaring animals can tell us a bit more about procreating.

Quite a number of animals have experienced various stages of reproduction in space. Sea urchin eggs and sperm were flown to space in 1965 on Gemini III to test the effect of microgravity on fertilization, but that experiment ended due to a mechanical failure. Later experiments showed normal fertilization in weightlessness, and normal development of such embryos back on the ground, but eggs exposed to microgravity appeared less able to be fertilized later in gravity.

Jellyfish could reproduce in space—but upon return to Earth, they had more trouble orienting themselves under gravity. The nematode Caenorhabditis elegans appeared to reproduce normally during the Shenzhou-8 mission (bear in mind, these critters can survive a shuttle crash). Snail embryos developed well under zero-g; so did brine shrimp larvae, butterfly cocoons, cricket larvae . . .

But these are all invertebrates. What about animals more closely related to us?

Rice fish mated and produced offspring successfully in the space Medaka experiment, being the first, and so far only, vertebrates completing their life cycle in space. Frog eggs were first shown to develop mostly normally in zero-g in Gemini VII and XII missions after on-ground fertilization, and just as promising were the results from the Biosatellite II experiments. Newts went through fertilization and early development in space without any major problems, though their development was slightly altered. Both males and females born in space were able to reproduce normally. Good news, then?

Birds fared worse, though. Most freshly laid eggs died in space, probably because in weightlessness, yolk failed to stay close to the shell, which impaired gas exchange. Eggs dispatched to space at later developmental stages mostly remained fine. Quail eggs flown to space hatched there, but the young suffered from behavioral problems and developmental abnormalities, and the fertility of adults was impaired.

To see if humans have a good chance of reproducing in space, we must look toward placental mammals. Only rats and mice were studied in this respect. Pregnant rats were flown to space several times and the pregnancies went mostly well (the placentas showed a little hemorrhaging, but that was associated with reentry rather than space itself). The litters born back on Earth had a slightly increased early mortality—worrying, but not necessarily associated with spaceflight.

What happens if we fly newborn mammals to space, though? Not much good, it turns out. When baby rats younger than two weeks traveled to space with their moms, most of them died. The younger the rats, the higher their mortality. Some were abandoned by their mothers; the stress of spaceflight seemed to have disturbed the parent-offspring bond, and even the surviving babies had lower body height and could experience dehydration, hypothermia and stress. Just like other vertebrates, they also had issues righting themselves in gravity, although these appear to be temporary.

These results do look quite frightening for the prospect of delivering a space baby (not speaking of the fact that no mammals have given birth in space yet). But would it even come so far? No mammal has yet completed a life cycle in a space environment and achieving successful fertilization and an entire pregnancy might be difficult. Estrus cycle stopped in female mice within just two weeks in space—essentially rendering them temporarily infertile. What was responsible, though—microgravity directly, or rather stress from the full set of conditions?

Regardless, it doesn’t look so good for us mammals. We even lack sufficient data on women’s reproductive health in space. Although most female astronauts forgo periods in space by taking combined oral contraceptives, menstruation in microgravity appears not to be a serious problem (at least not a medical one; it could become a logistical one on a long-term mission with limited supplies). But forgoing periods means we have little data about potential changes in the menstrual cycle and ovulation in space. Does the thickness of the uterus’ lining change substantially in microgravity? If so, how does it affect the chances of embryo implantation? We need rigorous gynecology studies in space, more female astronauts, and animal studies using mammals to find out.

At least it looks like space doesn’t impair fertility for long—although a lot of female astronauts returning to Earth have needed assisted reproductive techniques to conceive, it was likely due to age rather than spaceflight experience.

Other effects than the direct influence of microgravity and radiation on fertilization, pregnancy, and the baby could become apparent only in sufficient time and numbers—the stressors of spaceflight might potentially increase the risk of chronic diseases and metabolic issues, even across generations. Furthermore, what would the environment of a space station, ship, or settlement do to the microbiome of children born there? The microbiome is an important influence of our health, and its disturbance can lead to severe health issues.

The questions don’t end here. Luckily, as we venture further, we’ll have more opportunities to search for answers. Future animal breeding experiments on the Moon would help elucidate the role of space radiation, conditions in space settlements, and gravity needed for the successful development of various animals—and eventually humans. Would the low gravity on the Moon suffice for normal development? Does the influence of gravity on our physiology, including reproduction, act like a continuum, or is there a sharp spike—for instance humans being unable to procreate in microgravity, but able to reproduce just as well on the Moon as on Mars, Earth, and in slightly higher than Earthlike gravity?

So far, we can very carefully conclude that microgravity, increased radiation, and other conditions don’t prevent most animals—and perhaps wouldn’t prevent us either—from reproducing, but they seem to increase the risk of developmental problems and never have we witnessed the whole development of mammals—especially birth—in space. Would creating artificial gravity via rotating sections and thicker radiation shielding solve the problems observed in rats and mice? We’ll hopefully see in the years to come . . .

Still, human births are complicated enough on Earth, and no matter how many animal experiments we do, they are going to pose significant health risks. We’re paying the price for our big brains.

Another issue is that unplanned pregnancies might occur in space; no contraception is one hundred percent effective every time, although hormonal contraception has very high reliability. What would we do if a pregnancy occurred on a long-term mission with no chance of medevac? Procedures for an abortion should be in place—but what if the astronaut wanted to keep the baby? Would a continuation of her pregnancy even be ethical in light of the challenges faced by the mission (somewhat naïvely portrayed in the 2017 The Space Between Us movie)?

We have no good enough terrestrial analogue for that, but for a confined, demanding, and often dangerous environment, we can turn to Antarctica. Eleven babies so far were born on the southernmost continent, most because of a bizarre territorial claims race between Argentina and Chile. All of them were fine (so Antarctica can claim the lowest infant mortality rate in the world), but if trouble occurred, advanced medical help was too far away. But pregnancies carried to term elsewhere were recorded—Jennie Darlington, who overwintered with her husband in 1947/8, became pregnant there, and gave birth in the US. Australia has a record of at least seven pregnancies on its stations and supply ships (but no birth in Antarctica). The pregnant women traveled back where obstetrics care was accessible.

And we’re still at the issues of reproductive biology. What happens when we introduce psychology, social science, ethics? Some may scoff at the idea of these presenting potentially larger issues than “hard” sciences, but any human space settlement is going to stand and fall with them. Any group of people trapped in a confined space will experience conflict—how they handle it determines whether they survive. While astronauts go through a rigorous selection process, it’s not perfect, as Lisa Nowak‘s jealousy-induced incident shows. Relationship issues can arise even among trained professionals, and having children in the closed quarters of a space settlement might keep old wounds open without any possibility for some of the involved people to move away.

Even in a previously harmonious society, childcare might entice conflict rarely portrayed in SF. A lot of science fiction features parenting, but it’s usually focused on older children, rarely newborns, babies, and toddlers, and even less frequently depicting the challenges of raising children in space. There’s never enough emphasis on just how hard childcare can be.

Some parents may welcome perfectly happy babies into the world, while others may encounter a whole suite of problems, even if the child is essentially healthy—but what if she fusses a lot, has problems latching, or refuses the bottle in the case that the mother can’t breastfeed, or has hard-to-pinpoint food allergies necessitating a demanding elimination-exposure diet in the lactating mother, or all of those together? What if, once solids are introduced, the child simply refuses to eat and continues to do so even well into toddlerhood?

These instances are not as rare as you might think, and they’re stressful enough for the parents even on Earth in “ideal” conditions. In microgravity, our sense of smell gets weakened, and we consequently experience fewer sensations when tasting food. Astronauts typically need more spicy meals to enjoy them. And while some degree of gravity would be necessary to facilitate the development of the vestibular system and muscle control in babies anyway, would they like “bland” baby food in low centrifugal-induced gravity and dry artificial-smelling air? We could hardly throw in some chili for them. It’s possible that issues such as food refusal might become much more prevalent in space, and we still don’t know if spaceflight makes people more susceptible to allergies.

Now imagine these medical problems bleed into social and psychological ones: Developing anxiety in the parents and their social circle, possibly already stressed due to demanding work in a very “alien” environment (astronauts have reported suffering from insomnia, stress, fatigue, headaches . . . ). Creating demand for special conditions for the baby and parents, possibly eliciting disapproval from some of the crew (if your baby is able to suckle but refuses the bottle, you don’t want to do a long EVA; if they’re allergic to cow’s milk, you skip the whey protein drink and get extra rations of dried meat to get enough protein; if they’re only calm when wrapped close to you and no one else, you’ll probably have to find someone else for potentially dangerous lab duty . . . ). That is, if everything went well enough and there’s no previous conflict in the crew over the pregnancy and parenthood. Once we have more people in orbit and space settlements, including tourists and settlers going through less rigorous training and selection, conflicts might be hard to avoid.

And we haven’t gotten to the especially thorny ethical issues yet, such as the lengths we’re willing—or forced—to go in order to keep our space settlements functioning. In harsh conditions without an easy return to Earth, are we going to use genetic engineering or embryo selection to maintain a crew that is sufficiently genetically diverse so as to not be threatened by emerging diseases? How are we going to deal with potential disabilities? Are we going to limit the number of children people can have—and how? By incentives alone—or can we expect abhorrent practices such as forced abortion or sterilization to arise?

All of this, of course, depends on how we go about reproducing in space. A slower approach, reliant on setting up a lot of redundant infrastructure and creating regular travel routes before actually settling places, should help us avoid such dystopic measures. Unless we pile upon our mistakes, it’s likely that we’ll see some space settlements in this century. Some of them might remain relatively isolated for a few generations, with low inflow of new settlers—but within the solar system, genetic diversity might not be so much of an issue if a few people migrate here and there throughout the solar system in every generation.

However, if a generation ship to another star system is eventually launched, it won’t have this option, and might resort to more draconic measures, such as obligatory use of gene engineering, donor embryos, or reproductive partner matching (although even this problem might pale in comparison with others, many of whom were recently explored in fiction, e.g., in Kim Stanley Robinson’s Aurora). What if you had no choice whether to have children and how many? What if you were compelled to bear children with no genetic relation to you? What if you wanted a child, but were forced to have none because of limits on the number of the crew? On the contrary—what if you didn’t want to bear children, but were compelled to do so as a “duty” to your starship’s mission? These questions reflect some of the serious issues people are facing even nowadays across the world for very, very different reasons, and probably all of us would agree that we should strive to leave them behind both on Earth and in space.

We have far more questions than answers when we wonder whether and how we’ll be able to have children in space. To find these answers, we have to go out there: to space stations, the Moon, Mars. We’ll bring animals with us and watch them breed. We’ll do it in large enough sample sizes, with adequate control samples (on Earth as well as in space, exposed to gravity on a centrifuge) and with concrete questions in mind. Then, hopefully, we’ll manage to avoid creating an aimless “zero-g zoo” that some scientists warned of before, but will find the many important answers we’re looking for before trying for the first space-born human baby.

Author profile

Julie Nováková is a scientist, educator and award-winning Czech author, editor and translator of science fiction, fantasy and detective stories. She published seven novels, one anthology, one story collection and over thirty short pieces in Czech. Her work in English appeared in Clarkesworld, Asimov’s, Analog, and elsewhere. Her works have been translated into eight languages so far, and she translates Czech stories into English (in, Strange Horizons, F&SF, Clarkesworld, and Welkin Magazine). She edited or co-edited an anthology of Czech speculative fiction in translation, Dreams From Beyond, a book of European SF in Filipino translation, Haka, an outreach e-book of astrobiological SF, Strangest of All, and its more ambitious follow-up print and ebook anthology Life Beyond Us (Laksa Media, upcoming in late 2022). Julie’s newest book is a story collection titled The Ship Whisperer (Arbiter Press, 2020). She is a recipient of the European fandom’s Encouragement Award and multiple Czech genre awards. She’s active in science outreach, education and nonfiction writing, and co-leads the outreach group of the European Astrobiology Institute. She’s a member of the XPRIZE Sci-fi Advisory Council.

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