Human sperm don’t swim the way that anyone had thought

Rolling and lopsided tail flicks keep the cells moving in a straight line

illustration of sperm

In this illustration of a swimming sperm’s position over time, the head (red) rotates as the tail (blue) beats to only one side. The combination results in straight-ahead movement.

polymaths-lab.com

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.