Why do crabs walk sideways? Scientists trace it back 200 million years

Crabs’ famous sideways walk may trace back to a single evolutionary moment 200 million years ago. Researchers found that most modern crabs inherited this trait from one ancestor—and never looked back. The movement likely gave them an edge, helping them dodge predators with quick, unpredictable bursts. It’s a rare example of a behavior evolving once and then dominating an entire group.