A Stroke of Genius: New Research Shows That Sperm Don’t Slither—They Corkscrew

By 1677, Antonie van Leeuwenhoek had already begun to shape his legacy as the “father of microbiology.” In addition to constructing his own microscopes, the mostly self-taught scientist was the first to study microorganisms in pond water, calling them animalcules. So when a medical student named Johan Ham observed something that appeared to be alive in a human semen specimen, he brought it to van Leeuwenhoek.

Through the microscope lens, van Leeuwenhoek saw it, too: a “small earth-nut with a long tail” that we now know as sperm. After examining some of his own specimens, van Leeuwenhoek asserted that sperm propel themselves forward with “the motion of their tails like that of a snake or an eel swimming in water.”

For nearly 350 years, scientists have supported van Leeuwenhoek’s claim that human sperm move through liquid by lashing their tails from side to side. But a new study published in Science Advances shows that these cheeky little earth-nuts don’t slither like eels at all. Instead, they corkscrew like otters.

A group of researchers from the UK and Mexico used a high-speed camera and other microscopy devices to capture a sperm’s movement in 3D, which revealed that its tail actually only lashes to one side—and if you’ve ever tried to row a boat with one oar, you probably know that sticking to one side will send you spinning in circles. The sperm, however, have figured out a clever fix. They rotate their bodies every time their tails strike sideways, which pushes them forward in a corkscrew motion.

The reason van Leeuwenhoek’s original observation went undisputed for so long is mainly because scientists have continued to view sperm with 2D technology. Without depth, you can’t tell that the sperm’s body is spinning, and the tail looks like it’s simply moving to each side, rather than completing a rotation. And as Hermes Gadêlha, University of Bristol lecturer and co-author of this study, explained in his article for The Conversation, sperm’s size and speed make them hard to observe closely. In less than one second, they can complete about 20 propulsions.

While this study is significant for the mere shock factor of realizing we’ve been wrong for centuries, it could also impact future research on the causes of male infertility. In other words, having a better understanding of how sperm travel to eggs may help us understand why some make it there more easily than others.

[h/t The Conversation]