thinking makes it so

There is grandeur in this view of life…

Left over right and right over left

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I spoke last time about what I thought was one of Stuart Kauffman’s points in Reinventing the Sacred. This was that although you could explain for example a sand dune in terms of subatomic particles (by way of grains of sand and then silicon and oxygen ions), you couldn’t do the same thing if you started with a living organism. The living organism is an emergent real entity while the sand dune is not.

Now I’m not so sure. His Chapter 3, The Physicists Rebel, is about the inadequacy of reduction ‘even in physics itself’. But a number of times during the chapter I heard myself asking, ‘So what?’.

This is the second in a series on Stuart A Kauffman’s Reinventing the Sacred which began with Reinventing the sand dune.

Ammonia molecule

Ammonia molecule

Kauffman talks first about symmetry and asymmetry, drawing on the work of physicist Philip W Anderson. The ammonia molecule is a tetrahedron with a nitrogen atom at the top and three hydrogen atoms at the base. But it could also be envisaged as having the nitrogen atom below the three hydrogen atoms. And in fact the ammonia molecule oscillates between these two mirror-images, at an ‘inversion frequency’ of 3 x 1010 per second.

More complex molecules cannot do this however, so they exist as either left-handed or right-handed forms which cannot ‘flip’ between each other. (Apparently a right-handed glucose molecule could change over to its equivalent left-handed form by ‘quantum mechanical tunneling’, but not ‘during the life of the universe’.) In living organisms most amino acids are left-handed and sugars are right-handed. Kauffman describes this homochirality as an emergent ‘fact of life’.

The two optical isomers of amino acid alanine

The two optical isomers of amino acid alanine

It is probably also the occasion of my first ‘so what?’. I can understand that an ‘enzyme’ protein made of right-handed amino acids would not be able to do what the equivalent natural enzyme made of the same sequence of equivalent left-handed amino acids can do. I don’t know enough organic chemistry to know if it’s even possible for a mixture of left- and right-handed amino acids to string together to make a protein. Or if it is, whether there is any efficiency gain by ‘opting’ for either all left-handed amino acids or all right-handed amino acids. But it certainly seems plausible that early on in the development of life natural selection let metabolic pathways other than those based on left-handed amino acids and right-handed sugars fall by the wayside. Presumably pathways based on right-handed amino acids and left-handed sugars could have survived instead, but a chance event dictated that they didn’t.

I’m not suggesting I know the answer or that it’s an easy question. But it doesn’t appear to me to be a significant mystery in comparison to all the other things we don’t know. I can see that the inversion feature of an ammonia molecule is an ‘emergent’ fact about its structure, just as the virtual impossibility of a glucose molecule inverting would be an ‘emergent’ fact about its more complex structure. But I am not convinced that the ‘right-handed only’ rule about natural sugars was similarly emergent. Why couldn’t it have been chance?

Kauffman’s next example, also from Philip Anderson, is to do with computing.

I think I’ll leave that for next time!

© Chris Lawrence 2011.

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