Human Sperm Swim Like 'Playful Otters,' New Study Finds

Sperm cells are wobblier and wonkier than we ever imagined.

A new study has revealed that everything we thought we knew about sperm movement was a lie: Those persistent little swimmers don’t wiggle their way towards an egg like a snake, but rather roll around like an otter.

That revelation, published Friday in the journal “Science Advances,” came from scientists at the University of Bristol and the National Autonomous University of Mexico, who reconstructed the movement of a sperm tail using three-dimensional microscopy.

The researchers’ findings go against the observations of Antonie van Leeuwenhoek, the Dutch scientist often known as the father of microbiology who was the first to document bacteria and red blood cells.

Van Leeuwenhoek also just happens to hold the unique distinction of having studied his own sperm under a microscope in 1677, with his erudite ejaculate evaluation published by the Royal Society of London a year later. At the time, van Leeuwenhoek described his sperm cells as “animalcules” and observed that the sperm tail, “when swimming, ... lashes with a snakelike movement, like eels in water.”

The idea of this “snakelike movement” is an optical illusion caused by viewing sperm from above with a two-dimensional microscope, said Hermes Gadelha of the University of Bristol’s Polymaths Laboratory, one of the lead scientists on the study, in a statement. In reality, sperm wobble through the water in a manner quite unlike an eel, with their tails rotating repeatedly only on one side, like a spinning top.

“Human sperm figured out if they roll as they swim, much like playful otters corkscrewing through water, their one-sided stoke would average itself out, and they would swim forwards,” Gadelha said, calling this corkscrew method of movement “a swimming technique to compensate for their lop-sidedness.”

Gadelha added that the “otter-like spinning” of sperm might seem unusual but holds an inner complexity reminiscent of the planets. “The sperm head spins at the same time that the sperm tail rotates around the swimming direction. This is known in physics as precession, much like when the orbits of Earth and Mars precess around the sun.”

Alberto Darszon of the National Autonomous University of Mexico said that the discovery will “revolutionize our understanding of sperm motility and its impact on natural fertilization,” potentially providing new insight into how sperm swimming affects fertilization. He said the finding shows that there is still much misunderstood about the human body.

Sperm are very cheeky little creatures,” Gadelha told CNN. “Our new research using 3D microscopy shows that we have all been victims of a sperm deception.”

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