Understanding how life on earth evolved is an enduringly fascinating and profound question. Relative to our understanding of eukaryotic evolution, however, our understanding of how the molecular machines underpinning life have evolved is poor. The bacterial flagellar motor, which drives a rotary propeller for motility, offers a fascinating case study to explore this further, and is now revealing recurring themes in molecular evolution. This article describes recent discoveries about how flagellar motors have diversified since the first flagellar motor evolved, and what this diversity tells us about molecular evolution.

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