Friday 17 February 2017

CICÁDAMON GO?

Dick Pountain/Idealog 265/08 August 2016 09:54

Just back from a holiday in Southern France where I spent much of my time reclining in a cheap, aluminium-framed lounger under an olive tree in the 39° heat, reading a very good book. One day I went down to my tree and found a bizarre creature sitting on the back of my lounger: it was however not any member of the Pokémon family but "merely" a humble cicada. The contrast between a grid of white polythene strips woven on an aluminium frame and the fantastic detail of the creature's eyes and wings could have been an illustration from the book I was reading, "Endless Forms Most Beautiful" by Sean B. Carroll.

Endless Forms is about Evo Devo (Evolutionary Developmental Biology), written by one of its pioneers, making it the most important popular science book since Dawkin's Blind Watchmaker, and in effect a sequel. Dawkins explained the "Modern Synthesis" of evolutionary theory with molecular biology: the structure of DNA, genes and biological information. Carroll explains how embryology was added to this mix, finally revealing the precise mechanisms via which DNA gets transcribed into the structure of actual plants and animals. It's all quite recent - the Nobel (for Medicine) was awarded only in 1995, to Wieschaus, Lewis and Nüsslein-Volhard - and Carroll's book was published in 2006. That I waited 10 years to read it was sheer cowardice, now bitterly regretted because Carroll makes mind-bendingly complex events marvellously comprehensible.  And I'm writing about it here because Evo Devo is all about information, real-time computation and Nature's own 3D-printer.

I've written in previous columns about how DNA stores information, ribosomes transcribe some of it into the proteins from which we're built, and how much of it (once thought "junk") is about control rather than substance. Evo Devo reveals just what all that junk really does, and Charles Darwin should have been alive to see it. DNA does indeed encode the information to create our bodies, but genes that encode structural proteins are only a small part of it: most is encoded in switches that get set at "runtime", that is, not at fertilisation of the egg but during the course of embryonic development. These switches get flipped and flopped in real time, by proteins that are expressed only for precise time periods, in precise locations, enabling 3D structures to  be built up. Imagine some staggeringly-complex meta-3D printer in which the plastic wire is itself continuously generated by another print-head, whose wire is generated by another, down to ten or more levels: and all this choreographed in real time, so that what gets printed varies from second to second. My cowardice did have some basis.

However the even more stunning conclusion of Evo Devo is that, thanks to such deep indirection and parameterisation, the entire diversity of life on this planet can be generated by a few common genes, shared by everything from bacteria to us. Biologists worried for years that there just isn't enough DNA to encode all the different shapes, sizes, colours of life via different genes, and sure enough there isn't. Instead it's encoded in relatively few common genes that generate proteins that set switches in the DNA during embryonic development, like self-modifying computer code. And evolutionary change mostly comes from mutations in these switches rather than the protein-coding genes. Life is actually like a 3D printer controlled by FPGAs (Field Programmable Gate Arrays) that are being configured by self-modifying code in real time. Those of you with experience of software or hardware design should be boggling uncontrollably by now.

Carroll explains, with copious examples from fruit flies to chickens, frogs and humans, how mutations in a single switch can make the difference between legs and wings, mice and chickens, geese and centipedes. He christens the set of a few hundred common body-building genes, preserved for over 500 million years, the Tool Kit, and the mutable set of switches that make up so much of DNA are the operating system for it. I'll not lie to you: his book is more challenging than Blind Watchmaker (most copies of which remain unread) but if you're at all curious about where we come from it's essential.

But please forgive me if I can't raise much excitement for Pokémon Go. Superimposing two-dimensional cartoon figures onto the real world is a bit sad when you're confronted by real cicadas. Some of these species have evolved varying hibernation cycle times to prevent predators relying on them as a food source. To imagine that our technology even approaches the amazing complexity of biological life is purest hubris, an idolatry that mistakes pictures of things for things themselves, and logic for embodied conciousness. If the urge to "collect 'em all" is irresistible, why not become an entomologist?

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