Reproduction is a complicated business, and for many creatures on our world, its a rather lethal and painful experience, complete with disembowelment and impalement on genitals that could double as weapons in a typical Medieval arsenal. Thankfully, we humans tend to have it relatively easy and generally have the making babies thing down so much so, what when we’re talking about venturing into space, we wonder if we can take our kids with us and give birth to new generations as we travel to the stars. In fact one of the dominant ideas for getting to another solar system within the next few centuries involves the generation ship, vast spacecraft designed to function as their own, self-contained colonies and housing thousands of humans for very long stretches of time, ideally with all the comforts of home. And one of those comforts better be gravity because it turns out that if humans were to start reproducing without that familiar acceleration of 9.8 m/s/s or pretty close to it, their children are likely to be born with cranial defects, collapsed jaws, and buckled spines, among some of the other pleasantries of embryos’ inability to cope with a lack of gravity during the development process.
Building on some previous research into reproduction in space, a Canadian graduate student working with a sample of zebrafish embryos decided to temporarily free them from gravity at a developmental stage in which their skulls were being shaped. After spinning them in a bioreactor designed to simulate the perpetual freefall astronauts experience in space, she found that their heads simply didn’t form properly. Jaws were warped, and a number of bones at the base of the skull were deformed and buckled as the fish grew into adulthood. It seems that without the effects of gravity, the scaffolding for the diving cells is altered and the resulting bones, cartilage, and other structures assembled themselves on a faulty foundation. And the damage isn’t just to the skeletons either. An earlier experiment with zebrafish also found that the lack of gravity means that their basic senses were also severely affected. The improper distribution of fluids in the embryos damaged what would become their vestibular system. With a defective internal gyroscope, the fish has problems with stabilizing the movement of their retinas. Humans with a similar defect would be unable to keep track of objects in their line of sight were they to turn their head because their eyes couldn’t adjust. For most zebrafish, these effects were temporary if they were taken out in time, but the longer they stayed in microgravity, the more permanent those effects became. Human embryos in space are very likely to suffer the same fate as well.
Oh and by the way, all this is just from the development process. In the depths of space, as a spacecraft gets pelted with cosmic rays and solar winds, it’s hard to tell what radical and very likely deadely mutations would start surfacing in a floating embryo. Now of course, all these problems aren’t insurmountable and don’t say anything about our future in space. Spacecraft which rotate around a central axis, using centrifugal force as a stand-in for gravity could be built, and an electromagnetic shield would keep out a good deal of radiation. But that said, there would still be very serious risks when it comes to raising new generations away from Earth. It your craft were to break and find itself unable to keep spinning or a sudden power outage leaves the artificial magnetosphere severely reduced or down for any significant length of time, your descendants may suffer the consequences. How do we know that human children may be deformed as embryos in microgravity if we did the experiments on zebrafish? Because zebrafish and other vertebrates share a very similar set of key stages in development and thanks to evolution, we know that what affects the zebrafish is also far more likely to have an effect on us than not. So if we ever want to colonize and populate space, we better start building some very redundant and very reliable spacecraft that won’t just come with some of the comforts of home, but require all of them for the sake of our future astronauts children and grandchildren…
See: Moorman, S., Cordova, R., & Davies, S. (2002). A critical period for functional vestibular development in zebrafish Developmental Dynamics, 223 (2), 285-291 DOI: 10.1002/dvdy.10052
[ photo illustration by Tomas Pais de Azevedo ]