There is a remarkable fact about identical twins: they have the same DNA, and therefore the same ‘genetic fingerprint’, yet their actual fingerprints (such as they might leave behind on a murder weapon) are different, and can be told apart in standard police observations. Fingerprints are, of course, produced by the pattern of tiny ridges in skin. So, it would appear that certain fine-scale details of our anatomy cannot be determined by a precise ‘genetic blueprint’.
It isn’t only fine details that seem open to negotiation in this way: anyone who has seen Bonsai cultivation knows how the very genes that would normally build a large tree can instead build a miniature-scale model, given a suitable environment. Bonsai trees aren’t completely scaled down, of course: their cells are normal-sized – it’s just that each component is made with fewer of them.
Well, this neighbourhood isn’t GATTACA then.
The DNA helix is important, of course. But the most important thing it does is make proteins that can operate in regulatory loops. These loops can also operate at the molecular level: genes make proteins, but these proteins determine which genes are ‘off’ and which are ‘on’ (as HIF1A does), making a control loop at even the molecular level. Unlike the helix, loops also operate at scales far above the molecular, covering a range of sizes from bacterial colonies to the vast ecosystems of the rainforest – perhaps to the ecosystem of the entire Earth. Beyond Earth, life without DNA is just about thinkable (one can imagine alternative strategies for storing information). Life without feedback loops, though? I have never met any biologist who can imagine that.
The helix is too well-established an icon to be deposed any time soon. And yet, a simple loop would be a much more universal symbol of how life works at all of its scales and levels. Perhaps the Ouroboros, beloved of gnostics and alchemists, has been an ideal symbol waiting in the wings for centuries: there can surely be no more evocative symbol of feedback than a snake growing by devouring its own tail.
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