Left vs Right

BBC News: Sinister secret of snail’s escape.

Snails with left-handed shells can have a big advantage in life – predators may find it impossible to eat them. That is the conclusion of research just published in the Royal Society’s journal Biology Letters. Scientists from the US examined whelks and cone shells preyed on by the crab Calappa flammea. 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.

Handedness is not just a human trait. Crabs, shellfish, snails, walruses, it’s everywhere, and lefties are always in the minority. Why is that?

("Sinister" means left in Latin, "dexter" means right.)


  1. Handedness also exists in chemicals, where the right and left hand molecules can have quite different properties. All of the benefits of Thalidomide reside in one form, all the side effects in the other. Originally Thalidomide was sold as a mix, with the well known results. Now they run the drug through a chiral filter to sort all the “good” ones from the “bad” ones, and can sell the drug for morning sickness again. Amino acids comes in L and D forms, equally abundant. But the whole body uses only L forms. One of the mysteries of life – why have two forms when only one is used?

  2. Those of us forced to switch, or ambidextrous made to stop using one hand, still have the brain structure for the other side. My mother was switched, but after a head injury she reverted to being a leftie for a while.

  3. Jessica wrote “Handedness also exists in chemicals, where the right and left hand molecules can have quite different properties”

    In biology this is true, thanks to the specific way that proteins fold and shape their “receptors” for chemicals. When you have a test-tube of a mix of the left and right handed versions of a molecule, however, it’s extremely hard to differentiate because they have identical properties. When left to chance the 50/50 mixture of chemicals that behave identically in a test-tube environment shouldnt exert any influence one way or another over the proteins they would bind to. Chance would therefore dictate that proteins themselves should (similarly) handle a 50/50 mix of handedness. In reality they dont. There’s a clear “design decision” (to borrow a phrase common in the software industry) to go all one way (the “L” form).

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