Human Sperm Swim More Like Otters Than Eels, Study Finds

upstart writes in with an IRC submission for nutherguy:

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.

[...] Back in 1977, physicist Edward Purcell did some calculations that showed how animals of different sizes would swim at different Reynolds numbers. The number would be very high for a whale, for instance, which is able to coast a good distance with a single flap of its tail. According to Purcell's calculations, however, bacteria swim at low Reynolds numbers, so they can barely coast any distance at all if you push them to set them in motion. It's akin to a human trying to swim in molasses and moving their arms at slow speeds on par with the movement of a clock's hands. So eels and sperm (or bacteria) would adopt very different swimming strategies by necessity because they are dealing with different Reynolds numbers.

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