While rare in nature, many organisms including humans have some, but few, members that are lefties. Author Gregory P. Dietl, post-doctoral fellow in geology and geophysics at Yale has studied the survival advantages or disadvantages of being a "leftie" by working with snails and their predatory crabs.
"One of the conclusions we draw from the interaction between crabs and these snails is that in the adversarial mode, lefties have a competitive advantage as long as they remain rare," said Dietl. This parallels some social interactions in human cultures, such as sporting competitions in which left-handed players enjoy an advantage over their right-handed opponents.
The functional advantage of this rare reversal in shell-coiling direction, while a topic of fascination for scientists and laypersons alike, has evaded explanation. Persistence of handedness in snails is most often associated with a mating advantage. In this case, snails mate most effectively with snails whose shells coil in the same direction.
The overwhelming majority of snail species are right-handed -- their shells coil clockwise. Dietl studied a species of snail that are lefties, and have shells that coil counterclockwise.
The left-handed advantage is realized when snails interact with predators of opposite handedness. Some predatory crabs are "righties" -- and have a specialized tooth on their right claw that acts like a can opener to crack and peel the snail shells. "The 'sinistral advantage,' or advantage to being left-handed, is that it would be like using a can opener backwards for the crab to crack and peel the snail shell," said Dietl.
They measured the frequency of unsuccessful crab predation left as repair scars on the sn
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Contact: Janet Rettig Emanuel
janet.emanuel@yale.edu
203-432-2157
Yale University
23-Mar-2006