Human sperm swim more like otters than eels, study finds

For more than 300 years, most scientists have assumed that sperm "swim" through fluids by wriggling their tails back and forth like eels to propel themselves forward. But according to a new paper in Science Advances, this is actually an optical illusion—the result of viewing the creatures from above with 2D microscopes. New observations with 3D microscopy have revealed that human sperm actually roll as they swim, like otters, essentially corkscrewing themselves forward.

"With over half of infertility caused by male factors, understanding the human sperm tail is fundamental to developing future diagnostic tools to identify unhealthy sperm," said co-author Hermes Gadelha from the University of Bristol.

The honor of directly observing the first sperm rests with Antonie van Leeuwenhoek, a 17th-century Dutch draper with a side interest in science—specifically, building microscopes and coming up with innovative manufacturing methods to make better lenses for said microscopes. Only a few of his microscopes have survived, but they are capable of magnifying small objects up to 275 times, and historians believe some of his instruments could have achieved magnifications as high as 500 times.

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