If humans ever try to have babies in space, sperm may first need a navigation lesson. Australian researchers say that sperm exposed to simulated microgravity moved erratically—the Guardian notes they started "[tumbling] around like an untethered astronaut"—and were far less likely to reach their destination in a lab-built "reproductive tract" maze. Using a 3D clinostat to mimic weightlessness in space, the University of Adelaide team found about 40% fewer human sperm made it through compared with a control group.
Samples from mice and pigs showed similar issues, with early embryos from those animals also developing differently in microgravity. The work, published in Communications Biology, suggests that gravity plays a key role in how sperm orient themselves, though viable embryos still formed, which the scientists say keeps the prospect of off-world reproduction alive. Adding progesterone, a hormone naturally released by eggs, helped guide disoriented sperm, hinting at potential workarounds for future lunar or Martian settlements.
The study adds to decades of research on reproduction beyond Earth as NASA, SpaceX, and others talk openly about long-term human habitats in space. The research also underscores calls from scientists for more coordinated, ethically guided research on how microgravity and radiation shape fertility. "These insights show how complex reproductive success in space is, and the critical need for more research across all early stages of development," study co-author Nicole McPherson says in a release.
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