Day 052 - Where bodies came from

Submitted by Sam on 11 July, 2011 - 23:07

Intelligence arises from a society of unintelligent agents working together in very complex ways, emerging from a group of neurons that can, individually, be represented algorithmically. But where do neurons themselves come from? Where do all biological structures come from? How can evolution produce something so complex as an electrically-gated logic circuit from raw materials like carbon and hydrogen, insensibly pulling together groups of molecules to create structures as intricate as the organic computers that power the human brain?

In his seminal book The Selfish Gene, Richard Dawkins extends Darwin's theory of natural selection backwards in time to the inorganic precursors to life, lensing Darwin's principle of 'survival of the fittest' into the more general 'survival of the stable' to show how complex yet stable molecules 'evolve' from their constituent elements.

Chemists have shown how a sea of simple substances, like those that would have been found in the earliest environments on earth, can be stimulated with a source of energy, such as sparks (representing primordial lightning) or ultraviolet light, to produce molecules more complex than those originally present in the mix. Typically, after a few weeks, a 'soup' containing amino acids is created. Amino acids are the basic components of proteins, which are in turn the basic components of biological organisms. Dawkins saw that the earliest form of natural selection was therefore a selection of such stable molecular forms against a rejection of unstable ones, which would rapidly and automatically degenerate to be replaced by more robust forms.

Such a 'primeval soup' is believed to have constituted the seas thousands of millions of years ago, where clumps of organic molecules could become locally concentrated, perhaps combining into even larger molecules under the influence of energy from the sun or lightning. Through countless iterations of this process, Dawkins theorized that a singularly remarkable molecule was formed by accident – a molecule able to create copies of itself which he termed tht replicator.

A replicator could have acted as a mould or a template built from smaller building block molecules derived from the abundant soup, arranged in such a way that each building block had an affinity for its own kind. With this chemical propensity to draw together and bond, the building blocks would automatically join together into a sequence that would mimic (or inversely mirror) the shape of the replicator itself. If the chain ever split, there would be two replicators, and they would spread rapidly through the soup of building-blocks, making further copies of themselves.

This process would continue until the smaller molecular components in the soup became a 'contested' resource, placing a selection pressure on replicators which would favour any which might happen to form that used even larger molecules as building blocks. Non-identical replicators may have been created through copying errors in their 'parent' replicators, and these cumulative mistakes could have created molecules even more stable in the new environment than the old replicators. Perhaps new replicators formed by accident which were able to cannibalistically break down other replicators, decreasing their stabillity in order to obtain 'food' to fuel their own replication. In response to these 'proto-carnivores', other replicators may have been selectively favoured if their copying mistakes afforded them chemical or physical protection from their rivals, perhaps through a physical wall of protein which shielded them from chemical assimilation.

Dawkins shows that the replicators which would survive in this soup would be the ones that built 'survival machines' for themselves to live in, which would gradually get stronger and more elaborate as the competition for resources grew closer, and the competition itself grew more advanced. The culmination of these survival machines, and the marvellous conclusion to Dawkins' argument, is that genes are descended from the original replicators, and we are their survival machines.

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