When Lefty is Right

Evolutionary advantages of moving to the left

• Hannah Schardt
• Aug 01, 2006

EVERYONE KNOWS that pitching to a left-handed batter can be tough. Because of their relative rarity, lefties also have the upper hand in other sports: tennis, boxing, even basketball. This led Yale University geologist Greg Dietl to ponder whether some lefty animals might also be at an advantage when they go up against an aggressor. Dietl studies fossilized snail shells, including the few that are "left-handed," or counterclockwise-coiling. Dietl, along with colleague Jonathan Hendricks of the University of Kansas, found that lefty shells showed fewer of the healed scars that are signs of attempted predation. So he put live snails in a tank with snail-eating crabs, whose sharp right claws act like can openers on their prey. As Dietl predicted, when the shell-crushing crabs picked up lefty snails, they often failed to open them and simply gave up.