Monday, June 27, 2011
Life, for the fastidious
by Rishidev Chaudhuri
For the first week after I began taking a cell biology class I dreamed of deserts, vast sterile expanses of open heat with no living things, interrupted only by dreams of inter-galactic space and the structured infinity of mathematical forms. There is something profoundly disturbing and eerie about life at the molecular level. It is too purposive and awake to see it as inert matter – it is impossible not to anthropomorphize it or, more accurately, to attempt to make sense of its motives in the same way we do for people. And yet it is too alien to anthropomorphize in any useful way. Somehow, brute matter has figured out how to replicate itself and has exploded into a cacophony of form. Here proteins rush around cells carrying other proteins on their heads; other proteins slice and dice and reassemble yet other proteins. It is so easily seen as a parody of human ends. Looking into a microscope we are alienated from ourselves by our cells. We stare into a world of automata, a world made uncanny by the juxtaposition of its echo of and utter distance from our world.
To their credit, there is nothing explicitly malevolent about microscopic life or its components, even things as sinister as prions. The suspicion of matter that they induce is not the Gnostic horror of waking up and finding oneself trapped in a coffin that is actively conspiring to stay shut. And it lacks the single-mindedness of a thriving Schopenhauerian will to life. And neither is it the anguish of finding oneself alive in a universe indifferent to life; matter seems all too eager to become animate. If anything, we seem to find ourselves viewing matter in company with the early Buddhists, as life-creating but amoral. They, finding themselves doomed by nature to live (and suffer as an incidental effect), and for whom suicide was subverted by rebirth, sought to live so as to break the chain of causation and extinguish themselves.
Of course we don’t understand the strange frontier towns where inanimate matter begins to wriggle and repeat, though we have lots of interesting speculation about what might happen at those boundaries. In the molecular world of modern life, DNA stores information; this information is transcribed into RNA; and then some RNA is then translated into proteins, which carry out most of the functions of life. Among other things, proteins catalyze a host of reactions needed for life. In one possible origin-of-life scenario, RNA performs the functions of both DNA and proteins: it both stores information and catalyzes its own production and replication. Chains of RNA get longer and more complex, eventually beginning to co-operate with each other and to catalyze the assembly of amino acids into proteins. Eventually, the proteins take over much of the structural and catalytic work, and DNA, being more stable, takes over the information storage.
In an alternate scenario, metabolism precedes information storage and self-replicating genes. Autocatalytic metabolic cycles start to form on the surfaces of minerals near undersea hydrothermal vents, generating larger and more complex sets of organic compounds which eventually begin to store replicable information.
In a third possible story, life begins by inventing interiority. Molecules that have one end attracted to water and the other one repelled by it (delightfully named ‘amphiphilic’) self-organize into primitive cell membranes, like bubbles. Once life has identified and segregated its Other, the story goes, molecules trapped inside the membrane can encounter each other regularly and develop complex society shielded from the floating disorder outside.
Echoes of these ideas live on in some of the odd cast of almost-alive molecular beings that populate modern biology. Prions, famous as the possible cause of mad-cow disease, are self-replicating misfolded proteins: the structural defect is very stable and is able to propagate itself by causing other nearby proteins to misfold and so, zombie-like, forms copies. Viroids and plasmids are free-floating bits of RNA and DNA that can be autonomously replicated by the machinery of a host cell. Nanobes and nanobacteria are either really unusual crystal growths or very tiny DNA-containing cells, perhaps similar to the speculated primitive cell-membranes; no one is quite sure yet which they are. And these are probably only a tiny sub-sample of a diverse menagerie. We know next to nothing about the millions and millions of microbial life-forms in existence, with a diversity of genomes, shapes and strategies that dwarfs anything seen among animals. There are whole ecosystems among microbes that we play no part in and that we are only beginning to glimpse. Horizontal gene transfer might mean that evolution no longer happens by descent but by swapping bits of DNA (or RNA) between different cells, which would mean that our boundaries between species are irrelevant at this level (a taxonomist’s nightmare). There is also speculation about entire shadow biospheres that live undetected alongside us; for example, we’d be extremely unlikely to detect life based entirely on RNA.
There are visions of life that are less uncanny because they are more remote from us. It is not impossible that there could be some form of life in the giant clouds of gas and dust that lie in the vast almost-empty spaces between the stars and galaxies, and a number of people have speculated about self-organization in plasma, including the existence of structures like cell membranes. Some intriguing recent work used computer simulations to show that dust particles embedded in a plasma (as one finds in some interstellar and intergalactic clouds) could form self-replicating helical structures.
In a similar vein, inspired by Fred Hoyle’s novel “The Black Cloud”, Freeman Dyson envisages an organism composed of a large cloud of charge-bearing dust grains, communicating electromagnetically. He calculates that in a forever expanding universe, by slowing down its biological clock and hibernating for longer and longer fractions of time, the organism can survive on a finite store of energy forever, with its subjectively experienced time still being infinite.
Depending on your temperament, this vision of the end of the world might be a comforting triumph of life, thought and complex organization. Or it might suggest the horror of eternal return and the impossibility of nirvana, that the universe will not be allowed to calmly settle towards heat death and stasis but will be forcibly infused with sentient matter and compelled to reenact the same thoughts and gestures over and over for eternity.
 Tsytovich et al, New Journal of Physics 2007
 Dyson, Reviews of Modern Physics 1979. Obviously the paper is very speculative and there are many who disagree with the assumptions he makes to do the calculation. For example, the lack of a continuum of energy states or the existence of protein decay would be problematic for his argument.
Posted by Rishidev Chaudhuri at 12:40 AM | Permalink