Thursday, March 23, 2006


Comment: Symmetry and Asymmetry

This news item reminds me of the Palmer papers on symmetry and asymmetry in the Main Blog:

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.

'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."

The two papers are:

From symmetry to asymmetry: Phylogenetic patterns of asymmetry variation in animals and their evolutionary significance

"...Furthermore, because antisymmetry typically signals an environmentally triggered asymmetry, the phylogenetic transition from antisymmetry to directional asymmetry suggests that many cases of laterally fixed asymmetries evolved via genetic assimilation."

Symmetry Breaking and the Evolution of Development

"...First, directional asymmetry, an evolutionary novelty, arose from nonheritable origins almost as often as from mutations, implying that genetic assimilation ('phenotype precedes genotype') is a common mode of evolution."

For recent posts on genetic assimilation see:

Re: The evolution of adaptations (Waddington) (1) etc..

John Latter

Featured books from the Science and Evolution Bookshop:

"Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms and Cultures" (Amazon UK | US)

"Hemispheric Asymmetry: What's Right and What's Left (Perspectives in Cognitive Neuroscience)" (Amazon UK | US)

Other books on Symmetry from the Science and Evolution Bookshop: UK | US

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