Human reproduction in space is in doubt: it turns out that microgravity may prevent pregnancy.

“In light of the upcoming plans for long-duration space flights and the growing interest in space tourism, the topic of potential human conception in microgravity has become quite relevant,” reads an excerpt from an article by Spanish scientists published in the scientific journal Acta Astronautica. Their concerns stem not only from the increasing desire of volunteers to engage in sexual activity in Earth’s orbit but also from future prospects—specifically, the necessity of reproducing on the way to other planets.

On the Moon—the closest goal for humanity—the gravity isn’t much better: it’s only 1/6 of Earth’s. How will sperm, which are accustomed to Earth’s gravitational pull, fare in such and even worse conditions?

Researchers from the Technical University of Catalonia (Technical University of Catalonia) and Dexeus University Hospital divided each of the 15 samples of sperm collected from volunteers into two equal parts. Half was kept on Earth, while the other half was sent to microgravity—not in space, but in a brief period of weightlessness that can be artificially reproduced in a parabolic flight. As seen in the Russian blockbuster “The Challenge,” this method is also used to train future cosmonauts.

The exposure to microgravity was not prolonged, so the sperm underwent noticeable changes in that short time. Many sperm cells died, though not all. The survivors became sluggish and lost their orientation—the ability to purposefully swim towards the target, i.e., the egg.

- The negative consequences would have been even more significant if the exposure had been longer, - the Spanish researchers noted in their published article.

Thus, microgravity essentially has a contraceptive effect, which, according to the Spaniards, raises doubts about the prospects for reproduction in space “not only through traditional methods that have stood the test of time but also through assisted reproductive techniques such as in vitro fertilization (IVF), which may be necessary if we establish bases on the Moon or Mars.”

To put it plainly, it’s disheartening.

MEANWHILE

Physics Laws Don’t Apply to Sperm

The existence of sperm—male reproductive cells—has been known since 1677. The remarkable naturalist Antonie van Leeuwenhoek observed them through a microscope he invented himself, which provided nearly 300 times magnification.

Leeuwenhoek sketched the “little swimmers” and reported that they moved by whipping their tails, later named flagella.

Since then—since the invention of the first microscope, as is commonly believed—sperm swim towards the egg, wiggling their tails side to side, much like fish in water. This is precisely what is visible under the microscope—even in the latest models.

Ten years later—in 1687—Isaac Newton formulated his famous three laws of classical mechanics, which describe the motion of any systems for which the forces acting on the bodies are known.

Only over 300 years later did scientists inexplicably attempt to apply classical physics to the movement of sperm (as well as some single-celled algae with tails) and were surprised to find that they do not obey these laws.

As researchers from Kyoto University discovered, specifically, “little swimmers” violate Newton’s third law. They reported this in the journal PRX Life.

In modern terms (according to Wikipedia), Newton’s third law states: “material points interact with each other through forces that have the same nature, directed along the line connecting these points, equal in magnitude and opposite in direction.”

Sperm were exposed to microgravity

Or more simply: “for every action, there is an equal and opposite reaction.” Or even simpler: “action equals reaction.” This is a consequence of the uniformity and mirror symmetry of space.

Sperm swim in a very viscous medium—almost like jelly. However, they seem to swim as if they experience almost no resistance. In other words, they violate Newton’s third law.

The Japanese attributed a “strange elasticity” to the sperm tails, as they put it. Allegedly, thanks to this, by moving their flagella, the reproductive cells expend anomalously little energy. Yet, the scientists admitted they have not fully understood their mechanics.

For the sake of fairness, it’s worth mentioning that four years ago, British mathematicians from the University of Bristol (Department of Engineering Mathematics, University of Bristol, UK) shed some light on the mechanics of sperm and discovered that they behave more cunningly than just “fish in jelly.”

High-speed filming at 55,000 frames per second and the latest 3D microscope, which allows for volumetric imaging of examined objects, demonstrated that sperm do not whip their tails like fish or tadpoles. This is an optical illusion—a trick of perspective caused by a flat image. Instead, they twist their tails, which rotate in a spiral like a corkscrew, making about 20 rotations per second.

At the same time, the “little swimmers” dart their heads, allowing them to move both in a straight line and to maneuver.

If we track the successive positions of a sperm tail, it turns out that it performs helical movements

Whether this cleverness can be wholly blamed for the violation of Newton’s law is unknown. But partially, certainly.

Returning to space, it is worth noting: it is possible that microgravity somehow suppresses the ability of sperm to twist their tails so cleverly. It acts physically, so to speak. Although the Spaniards do not rule out that “perhaps there is some shift in the chemical processes necessary to maintain the health of sperm.” They plan further research in hopes of gaining clarity.