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:
"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:
"...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."
"...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:
Featured books from the Science and Evolution Bookshop:
Wednesday, March 22, 2006
Re: Coming Soon: Evolution of the Lateral Line into the Ear
I haven't had much internet time for the last few days (and I'm likely to be busy until the weekend) but I thought I'ld post an 'update'.
Looking into the lateral line has certainly proved interesting - some possibilities have evaporated while others have appeared in their place - but my overall impression at the moment is that it may be more profitable (in terms of time invested) if I put this on hold and then come back to it later. I'll see how it goes!
technorati tags: lateral+line
Sunday, March 19, 2006
Coming Soon: Evolution of the Lateral Line into the Ear
On Monday I posted this Nature news item to the General Evolution News category:
"Why is our cochlea, the key organ of hearing, curled into a spiral? It has been often thought to be a space-saving measure. But researchers in the United States have shown that the spiral could be vital for increasing our ear's sensitivity to sound, particularly at low frequencies.
Daphne Manoussaki of Vanderbilt University in Nashville, Tennessee, and her colleagues believe that the snail-shell curve of the cochlea focuses sound waves at the spiral's outer edge, making it easier for vibration-sensitive cells to detect them1.
If the researchers are right, then the ear is more sophisticated than we thought. "
Not only is the article interesting in itself, but it brought to mind something I read sometime ago concerning evolution of the lateral line into the ear, and I thought it might make a good example of how such questions can be approached from the perspective of the proposed internal evolutionary mechanism.
I've spent quite a lot of time today trying to establish a 'baseline' from which to proceed, making sure I've got my facts right etc., but it may be that the notes will be very brief. It's a question of starting from the 'top' and then deciding how far down the hierarchy to go - I'll probably spend more time on creating the jpegs! Anyway, the post should give an insight and hopefully will be ready by Wednesday at the latest.