Left-Handed Snails Are Impossible for Crabs to Eat.

Gregory Dietl of Yale University and colleagues found that snails with left-handed cones are impossible for predators to eat.

They found the crab is unable to open left-handed shells because it only has a tool for peeling them on its right claw; so it discards them.

"The crabs have a special tool on their claw, a tooth that's used like a can-opener," said Gregory Dietl from Yale University.

"So, if you imagine trying to use a right-handed can-opener with your left hand - it's very hard to do," he told the BBC News website.

Despite this evolutionary advantage, however, left-handed forms remain rare.

Link