Some of the world’s wealthiest and most influential people remain deadset on leaving Earth behind for a new life in outer space. But despite what they may think, life among the stars is not simply a matter of developing the technology and logistics to get us there. Humans have uniquely evolved over millions of years to thrive on Earth—alter any of those conditions even slightly, and it’s liable to cause all sorts of problems.

Among the many potential issues, life in space may wreck our kidneys, increase the risk for numerous diseases including cancer, and even fundamentally alter our DNA. Now, a team at Australia’s Adelaide University have found another possible roadblock. Humans in space may have trouble simply making new humans.

“This is the first time we have been able to show that gravity is an important factor in sperm’s ability to navigate through a channel like the reproductive tract,” said Nicole McPherson, a biomedical researcher and co-author of a study published today in the journal Communications Biology.

McPherson and her colleagues examined how zero gravity (or zero-G) conditions affect the sperm of three different mammals, including humans. Since hitching a ride into orbit was unlikely, they placed the samples in a 3D clinostat machine instead. This device simulates zero-G by flipping and disorienting the cells placed within it. 

They then put the sperm cells in an artificial maze built to resemble a female reproductive tract. In each instance, the cells had immense difficulty navigating what should have been a relatively straightforward path.

“We observed a significant reduction in the number of sperm that were able to successfully find their way through the chamber maze in microgravity conditions compared to normal gravity,” McPherson explained. “This was experienced right across all models, despite no changes to the way sperm physically move.”

The problems didn’t end there, either. After four hours in zero-G conditions, mouse sperm fertilized 30 percent fewer eggs than they do under standard conditions. Longer time in the space simulation worsened the issues, too.

However, it wasn’t all bad news for the little swimmers. The researchers discovered that supplementing human sperm with the sex hormone progesterone—critical for successful pregnancies—helped improve the odds of fertilization. According to McPherson, this may be because eggs also produce progesterone to help guide sperm. Still, they cautioned more analysis is needed before reaching a definitive conclusion.

Moving forward, the team is preparing to study how different gravitational environments like those experienced on Mars or the moon may affect sperm and embryo development. They will also explore how artificial gravity systems influence reproduction. At the moment, it certainly looks like it’s harder to make space babies than make them at home—but not impossible.

“Many healthy embryos were still able to form even when fertilized under these conditions,” McPherson concluded.This gives us hope that reproducing in space may one day be possible.” 

 

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