We've long pictured human sperm wriggling like tadpoles or snakes. New research reveals they actually roll like playful otters.
For over three centuries, scientists misunderstood sperm motility. In 1677, Dutch microscopist Antoni van Leeuwenhoek described sperm whipping their tails like eels or snakes to reach the egg (PDF in English / 5 pages). But a groundbreaking study published in Science Advances on July 31, 2020, by researchers from the University of Bristol (UK) and the National Autonomous University of Mexico proves this wrong.
The "snake-like" motion? It's an optical illusion from 2D microscope views.
Using advanced 3D microscopy, the team revealed sperm's true asymmetrical, corkscrew-like form. They don't propel forward by tail-whipping; instead, they rotate around their axis—like otters tumbling in water—to maintain balance and direction.
"The otter-like rotation of human sperm is complex: the head spins as the tail rotates in the swimming direction. This is known in physics as precession, similar to how Earth and Mars' orbits precess around the sun," explains a press release on the study.
Why does this matter? Understanding sperm locomotion precisely could improve fertility research and clarify human reproductive biology misconceptions.
Here's the model from the study:
