Since the dawn of the space age, advocates have urged us to seek out new homes in the heavens and colonize other planets. But our long-range survival depends on our ability to successfully reproduce and propagate our species. No one yet knows how possible this is. Experiments have been conducted on a wide range of organisms—including invertebrates such as sea urchins and fruits flies; animals like fish, frogs, salamanders, birds, and rodents; and, in some sense, humans—to see how they respond to off-world gestation. Certain results have proved promising, but a great many more point to the extreme challenges that await us when we decide to have families somewhere other than Earth.
The creatures with perhaps the best chances for long-term living in space might be fish. Medaka, or Japanese rice fish, have the distinction of being the first vertebrates to mate in orbit. An aquarium full of them flew on Space Shuttle Columbia in 1994, and their fry turned out completely healthy, even growing up and giving birth to a second generation of medaka once back on the ground. Based on their success, one researcher concluded in a 2004 paper that “fish are the most likely candidates to be the first vertebrate to live their life cycle in space.”
Experiments on other animals have been a mixed bag. Frogs that lived on the Space Shuttle produced tadpoles in space with few problems and salamanders gave birth to mostly healthy baby salamanders aboard the Russian space station Mir. Quail and chicken eggs, on the other hand, have shown extremely high mortality rates when flown in space. Researchers are still unsure exactly why this is but experiments that included turning the eggs—something that hens do naturally during incubation on Earth—increased the number of surviving chicks.
Invertebrate gestation experiments in space have mostly shown poor results. Sea urchins that flew aboard NASA’s Space Shuttle in the 1990s developed unusually slow sperm and their embryos showed genetic and developmental abnormalities. Another shuttle flight carried a swinging fruit fly party—240 female and 90 male Drosophila melanogaster. But after the flies got busy in zero-g, a significant numbers of their eggs failed to hatch and around a quarter of the larvae that came back to Earth failed to develop into adults.
The earliest investigations into mammalian pregnancy in space happened on the Soviet Cosmos 1129 biosatellite in 1979, which carried a crew of male and female astro-rats. Though the females were ovulating during their time in space, none came back expecting any offspring. A post-flight examination revealed that two of the rats had gotten pregnant, but the embryos were reabsorbed before developing further (nobody knows why this happened).
Later rodent experiments have had varying results. When researchers placed just-fertilized mice eggs in a 3D clinostat—a device that mimics zero-g—and then implanted them in mothers, the embryos tended to develop abnormalities and fewer numbers survived to birth than a control group. This suggests the earliest parts of development are significantly affected by altered gravity conditions. But fetuses that develop during the later stages of pregnancy seem to be fine. When already pregnancy mice and rats spent time on the Space Shuttle and International Space Station and came back, their pups tended to be healthy. Other experiments have shown damage to reproductive organs, such as decreased sperm counts in males, due to weightlessness. The ovaries of female mice that spent 13 days in space essentially “shut down,” according to the author of a 2011 study.
Human pregnancy in space remains the final frontier. Experiments obviously have a difficult ethical dimension in this case and, so far, none have been conducted. But the first woman in space, cosmonaut Valentina Tereshkova, gave birth to a healthy baby just a year after returning from her orbital flight in 1963. Since then female astronauts and cosmonauts have gone on to give birth to a total of 17 babies, suggesting that human reproductive organs aren’t particularly affected by short stays in space. Still, most researchers predict problems for longer duration missions.
Radiation in deep space is one of the biggest hazards to reproduction. Embryos are especially susceptible to damage from radiation and high-energy particles, which crash into DNA like sub-atomic bullets and cause genetic malfunctions. The sun is a major source of such threats, as is radiation from our galaxy, and neither can be adequately shielded against during an outbound flight to another planet. NASA researcher Tore Straume told Space.com that “the dose of radiation received by a fetus on a trip to Mars could likely result in severe mental retardation or other deficits.”
Will these problems be showstoppers in our efforts to colonize the stars? Perhaps, perhaps not. It’s possible that we will develop better protection against radiation or artificial gravity chambers for long-term space voyages. Maybe the lower gravity available on Mars and other planets will be enough to trigger normal embryonic development. But it seems that as we crawl out onto the shores of the cosmic ocean, human beings might become amphibian-like, forced to return to our ancestral homelands in order to reproduce.