Plants are Parallel Processors
It’s that time of year when gardeners can’t keep up with the burgeoning growth of their plants. We can only tackle one job at a time and behind your back everything else is growing at a phenomenal rate. The coronavirus is doing the same thing and there’s a link which I doubt many gardeners have reflected on.
My title is deliberately provocative: what has the lovely organic, homely garden got to do with this alien-sounding parallel processing, a term from computer chip technology?
Everything it turns out. The reason that the garden teems is that the way nature builds plants is radically different to the way that we build pretty well anything. The gardener can only plant one seed at a time, tie up a straggling climbers one at a time. But every living thing starts from a single cell which, left to its own devices divides, the resulting 2 cells dividing again, and again and again. This is the exponential growth we hear so much about during the pandemic.
The power of this is often illustrated by the parable of the rice and the chess board. As the story goes, when the game of chess was presented to a great king, the king offered the inventor any reward that he wanted. The inventor asked that a single grain of rice be placed on the first square of the chessboard. Then two grains on the second square, four grains on the third, and so on. Doubling each time.
The king, baffled by such a small price for a wonderful game, immediately agreed, and ordered the treasurer to pay the agreed upon sum. A week later, the inventor went to the king and asked why he had not received his reward. The king, outraged that the inventor hadn’t been paid, summoned the treasurer and demanded to know why the inventor had not been paid. The treasurer explained that the sum could not be paid — by the time you got even halfway through the chessboard, the amount of grain required was more than the entire kingdom possessed.
From the one grain of rice on the first square of the chessboard, the amount increases to the point that by the time you get to square 64, there are over 18 quintillion grains of rice on the board. It’s exponential growth, doubling at each round of cell division.
If it’s a virus or a bacterium, the result is just a lot more of them all the same; quintillions. If it’s a multicellular organism like plants the result is trillions of cells all developing according to the plan of the species. Nature only has this method of of building: cells divide and the progeny do the same.
All of which shows why Eric Drexler and his fantastical mechanical nanomachines were so far off the mark. Drexler is, after Richard Feynman, the most famous early prophet. of nanotechnology. In the early 1980s, he conjured a world like nano-Lego: hard, cold molecular gear-wheels and motors made from individual atoms, assembled one by one. The absurdity of this can be seen looking at the structural complexity of nature’s protein nanomachines: the engines of all life.
Humira, the best selling drug in the world has the chemical composition C6428 H9912 N1694 O1987 S46. That is 20,067 individual atoms. It is derived from a natural protein structure, evolved in the lab to target another protein, tumour necrosis factor, which causes, among other things, autoimmune diseases such as rheumatoid arthritis and multiple sclerosis. Can it be made atom by atom? Of course not. Just to create a single molecule by adding one atom at a time would be a herculean task, if possible at all. By why bother? To create the quintillions of molecules that would make a macroscale drug that could actually be used would be a task like that in Borges’ short story The Library of Babel, which imagines a library in which every conceivable book of 410 pages made of 25 characters is kept.
In fact, Humira is made by genetically modifying one of nature’s existing proteins, the product of billions of years of evolution. As Francis Arnold, the 2018 Nobel Prize Winner for Chemistry, wrote: “Since designing enzymes is still beyond our capabilities for anything but the simplest of reactions, it makes sense to look to the very effective evolutionary mechanisms nature has devised and exploited”.
Prodigiously large virtual objects can be constructed one entity at time: it the way the standard general purpose computer works. The reason it can achieve this is that its central processing unit runs at fabulous speeds. Nevertheless, parallel processing was developed to overcome the drawback that every instruction has to flow through the chip one at a time.
Unless you’re a researcher like Frances Arnold, it’s not possible to visualise the processes that enable plants to run quintillions of complex reactions simultaneously to build the plant’s structure. The reactions, running in parallel in each cell, enable them to double at each division, as in the rice board parable. 1 2 4 8 16 32 64 128 256 512 1024 2048 4096 etc — at the bottom end of the scale, the numbers are familiar from the pagination of print books, at the higher end from computer chip specifications. In plants, not only do the cells double in number at each round of divisions they multiply more in some directions than others to create the intricate shapes of leaves and flowers.
In the lockdown, more people than ever are growing plants from seed, enabling them to see the process at least on a low resolution macro scale. The plant I’m most intrigued by is Cobaea scandens, the Cup and saucer vine which after a very slow start — 1,2 4 8 16 etc — becomes a prodigious climber, climbing several inches a day at its peak.
Watching this gives some insight into the reason technologists now want to use nature’s parallel processing to create useful chemicals — drugs, fuels, paint, plastics , glues etc. As Frances Arnold has said:
Life — the biological world — is the greatest chemist and evolution is her design process. …I dream of the day that much of our chemistry becomes genetically encodable, and microorganisms and plants are our programmable factories.
An alternative dream to Drexler’s.
From a different angle, a plant like Cobaea reveals a staggering living force that calls for a poetic appreciation. This is Camille Paglia’s dithyrambic evocation of nature’s power:
A mind that opened itself fully to nature without sentimental preconception would be glutted by nature’s coarse materialism, its relentless superfluity. An apple tree laden with fruit: how peaceful, how picturesque. But remove the rosy filter of humanism from our gaze and look again. See nature spuming and frothing, its mad spermatic bubbles endlessly spilling out and smashing in that inhuman round of waste, rot, and carnage. From the jammed glassy cells of sea roe to the feathery spores poured into the air from bursting green pods, nature is a festering hornet’s nest of aggression and overkill.
Sexual Personae: Art and Decadence from Nefertiti to Emily Dickinson, 1991.
