Friday, December 14, 2012

The Algorithmic Origins of Life

Revolutionary Paper Tackles Definition of Life. 
In the newly published paper “The Algorithmic Origins of Life,” (1) Paul Davies and Sara Walker try to tackle the definition of life, and its evolution, from an informational system perspective rather than from the chemistry and the physical properties of the molecules that might have existed at the time on the planet. This is a unique and quite revolutionary way of re-conceptualizing what defines life and what would be needed to sustain, reproduce and evolve it.

Logical First Steps?
They begin by reviewing the analog versus the digital systems of information. The cell contains both an analog system (the continuous biochemical interactions between molecules in the cytoplasm) and a digital system (DNA) which is separate. Presently the favored idea of the original molecule of life is RNA. But as the paper argues, RNA is an extremely unstable molecule, susceptible to degradation by hydrolysis and difficult to synthesize in the first place under the conditions originally present on earth.
In addition, having RNA as both the digital carrier of information and as the biochemical catalyst that processes such information to control its environment is theoretically suspect. They argue that an analog system of a collection of molecules that interact to control their local environment would have been a more logical first step in information control. This system, however, suffers from an inability to adapt.

“Both the traditional digital-first and analog-first viewpoints neglect the active (algorithmic or instructional) and distributed nature of biological information.”

Trivial and Non-Trivial Replication. 
The challenge is to explain “how the instructional  information control systems emerge naturally and spontaneously from mere molecular dynamics.” To do this they employ the concepts of trivial and non-trivial self-replication. A system using trivial self-replication relies strictly on physics and chemistry to reproduce itself (crystals). Non-trivial replication, on the other hand, possesses active information which allows the molecule or system to create itself and objects other than itself (DNA can replicate itself and also has the code for creating proteins). The paper defines the emergence of life as the transition between trivial and non-trivial replication.

Top Down Information. 
Furthermore, non-trivial systems have been found to emerge when information flow in a system shifts from bottom up to top down (the molecules in the whole system are “the top” which influence the DNA-“the bottom”). Thus the emergence of life can further be defined as the transition to top down information flow.

Was Darwinian Evolution the First Step?
The paper concludes with the statement that “the onset of Darwinian evolution in a chemical system was likely not the critical step in the emergence of life.”  Instead, “the emergence of life was likely marked by a transition in information processing capabilities.” The cellular system as we know it today consists of bidirectional information flow—DNA passes its information to create proteins but is also influenced by those same proteins in what it expresses and when.

Questions abound, such as: How did digital RNA combine with analog molecules to create a hierarchy of information that would flow bidirectionally and thus benefit both itself and its compatriot molecules? 

Immortal Creator?
Nevertheless, this new theory that information is the driver of evolution echoes the physicists who ultimately arrive at the conclusion that information (the laws of mathematics) is the "immortal" element in the creation of the universe.

1 comment:

  1. The "top down" flow of information, which I think means downstream products influencing DNA precursors, hints at how environmental pressures might affect DNA directly and therefore accelerate the development of a certain trait. To add to the complexity, it is possible that the downstream products themselves might alter the local environment which, in turn, alters the precursor DNA: creating a self-enhancing or destroying feedback loop.


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