A closed loop

The DNA helix gave 20th-century biology its symbol. But the more we learn, the more life circles back to an older image

Twentieth-century biology was dominated by a strongly reductionist agenda even before James Watson, Francis Crick, Rosalind Franklin and Maurice Wilkins revealed the structure of DNA in 1953. Early geneticists knew perfectly well that they were studying statistical correlations (if one makes such-and-such a change in gene x, then allows the organism to develop in a fixed environment e, one will observe alteration f, etc). In later generations, however, the language of causation started to creep in, and with it the idea of a fixed relationship between genes and body features. Every reader of this essay will have read or heard phrases such as ‘the gene for breast cancer’, ‘the gene for autism’ or even ‘the gene for intelligence’ (try typing any of those phrases into a search engine). The cultural idea that went with this slip of meaning – that bodies are made according to a genetic blueprint – placed genes at the centre of mainstream biological thought. The discovery and progressive unravelling of the double helix seemed only to confirm their place there.

Where any part of the mechanism is sensitive to the environment, the whole self-organising loop can be too. The number of red cells in blood, for example, is set by a feedback loop sensitive to measurements of oxygen deep in the kidneys. When someone goes to live in the thin air of a high mountain, they tend to have more blood cells. Why? Because the ‘normal’ complement of cells is not sufficient in that environment, so the kidneys sense abnormally low oxygen and signal for more blood cells to be made. The effects of environmental sensitivity at a single point percolate throughout the entire organism. If we recognise that genes do not make body features, they make the machines that organise body features adaptively, that shift in perspective does much to lay to rest the long debates about nature versus nurture.

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.

More: http://aeon.co/magazine/science/why-the-symbol-of-life-is-a-loop-not-a-helix/?utm_source=Aeon+newsletter&utm_campaign=9c7bfbc00d-Weekly_Newsletter_26_Sept_20149_26_2014&utm_medium=email&utm_term=0_411a82e59d-9c7bfbc00d-68643017

Par to būs jādomā nākotnes robotu būvētājiem: atgriezeniskās saites mikrolīmenī (mehānisko kustību mācīšanās) un makrolīmenī (savas izturēšanās vērtēšana un pārvaldīšana). Ja mēs robotiem iedosim arī emocijas (bez tām viņi nespēs mūs saprast un mēs neuztversim viņus kā sev līdzīgus), tad balanss starp šīm abām pasaulēm būs grūts uzdevums. I.V.


About basicrulesoflife

Year 1935. Interests: Contemporary society problems, quality of life, happiness, understanding and changing ourselves - everything based on scientific evidence.
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