Human sperm don’t swim the way that anyone had thought
Sperm have long fooled scientists. Instead of swimming straight by twirling their tails like propellers, human sperm flick their tails lopsidedly and roll to balance out the off-center strokes. Over 300 years ago, microscopy pioneer Antonie van Leeuwenhoek described sperm tails swaying in a symmetric pattern, like “that of a snake or an eel.” The prevailing view that sperm tails move in a balanced way, however, doesn’t capture what actually happens in three dimensions, researchers report July 31 in Science Advances. High-speed 3-D microscopy of human sperm swimming freely in the lab revealed that the cells corkscrew as they move, consistent with previous studies. The sperm almost seemed to be drilling into the surrounding fluid, says Hermes Gadêlha, a mathematician at the University of Bristol in England. Contrary to what people have thought, sperm tails don’t beat symmetrically. High-speed 3-D microscopy and mathematical analyses reveal that the tails wiggle to only one side...