Can humans reproduce in space? The short answer is we don’t know. The long answer is maybe, but there are significant hurdles to overcome to make zero gravity pregnancy safe, and research into this topic is just beginning.
Space is a dangerous place no matter who you are. Astronauts who are in peak physical condition often return home after extended periods in space to find themselves weak, their muscles atrophied and their eyes damaged. Many of these effects are reversible, but some are not, such as the doses of solar radiation you receive that may lead to cancer later in life. Much of the experiments on the International Space Station are designed to advance medical science and alleviate the worst of these problems. But there’s more to learn, and when it comes to pregnancy, we know very little.
What we do know is that the real danger to developing human embryos is not radiation: it’s gravity. Or rather, the lack of gravity. In the early stages of the process, as cells begin to divide and grow, growth can occur more rapidly at one end of the embryo than at the other, and there is some evidence that gravity plays a role in this variation. Subsequently, gravity helps ensure that the body is shaped correctly, with cells appropriately oriented and in the right places. It is unclear what will happen to the development of human embryos in microgravity.
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Like other areas of medicine, animal testing can help scientists understand processes at work without risking human life. The first tests, going back to the days of the Gemini program, were conducted on frog eggs. The researchers found no abnormalities in cell division – a good sign. Soviet researchers tried to do fertilization tests on the fish, but struggled to get them to mate—it wasn’t until the space shuttle flight in 1994 that researchers succeeded in encouraging fish mating and spawning in space, and even then, only certain species seemed to adapt well. for microgravity. Other research in the 1990s found that 81% of newborns born in space developed neural tube abnormalities – but this was reduced to 23% when the newts were placed in a centrifuge, creating artificial gravity at 1G.
Birds and geckos have been studied similarly, but if we really want to understand human evolution in space, we need to study mammals.
The droppings of young mice studied in microgravity offer some good news and some new bad news. The good news is that many healthy rats and mice survived their spaceflights, after which they adapted to life on Earth without problems. Fearful flaws – changes that can last for generations – are not realized. The bad news is that a few of the newborns have shown ill effects, but the jury is still out on whether the cause was microgravity, or rather poor maternal care, as the mother behaved differently in microgravity and could not bind to offspring as they do on Earth. This lack of parental care can easily explain flaws such as a lack of attractiveness. More research is necessary.
Human development depends to some extent on embryonic stem cells: these are versatile cells that can develop into any type of cell the body needs. Unfortunately, there is some evidence that this process may be hampered in space. This is bad news for the possibility of pregnancy in space. On this front, too, it’s not all bad news. Stem cells from adult tissues – often used in treatments for degenerative diseases – appear to grow faster in microgravity, making these treatments better available to those who need them.
In the long term, if reproduction and pregnancy in space are to be safe, progress is needed in one of the two areas. We can attack the problem from an engineering point of view, developing rotating space habitats that simulate 1G by artificial gravity. Or, from a medical point of view, we can find ways to aid fetal development at the cellular level, perhaps through drug therapy.
Currently, Earth’s gravity (and possibly other gravitational wells, such as Mars), are the safest havens for pregnancy and childbirth. Leaving the proverbial cradle would not be a trivial matter. In this case, Mother Earth is a fitting embodiment of our planet, our reproductive systems here alone have evolved to function, and moving our biology beyond that will require creative adaptation, both technological and medical, to have hope of success.
Joanna Bridger and Emmanuel Cartres, “Pregnancy in Space: Studying Stem Cells in Zero Gravity May Determine If They’re Safe.” Conversation. 2022.
Alexandra Proshchina et al. “Reproduction and early evolution of vertebrates in space: problems, outcomes, and opportunities.” Life (Basel). 2021.
Featured image credit: Steve Jurvetson, cropped, https://creativecommons.org/licenses/by/2.0/deed.en