An information-processing approach to the origin of life
December 17, 2012
A novel approach to the question of life’s origin, proposed by two Arizona State University scientists — Paul Davies, an ASU Regents’ Professor and director of the Beyond Center for Fundamental Concepts in Science, and Sara Walker, a NASA post-doctoral fellow at the Beyond Center — in an open-access Journal of the Royal Society Interface paper, attempts to dramatically redefine the problem.
The authors shift attention from the “hardware” — the chemical basis of life — to the “software” — its information content. They suggest that the crucial distinction between non-life and life is the way living organisms manage the information flowing through the system.
“We propose that the transition from non-life to life is unique and definable,” said Davies. “We suggest that life may be characterized by its distinctive and active use of information, thus providing a roadmap to identify rigorous criteria for the emergence of life. This is in sharp contrast to a century of thought in which the transition to life has been cast as a problem of chemistry, with the goal of identifying a plausible reaction pathway from chemical mixtures to a living entity.”
“Chemical based approaches,” Walker said, “have stalled at a very early stage of chemical complexity — very far from anything we would consider ‘alive.’ More seriously they suffer from conceptual shortcomings in that they fail to distinguish between chemistry and biology.”
“To a physicist or chemist life seems like ‘magic matter,’” Davies explained. “It behaves in extraordinary ways that are unmatched in any other complex physical or chemical system. Such lifelike properties include autonomy, adaptability and goal-oriented behavior — the ability to harness chemical reactions to enact a pre-programmed agenda, rather than being a slave to those reactions.
“We believe the transition in the informational architecture of chemical networks is akin to a phase transition in physics, and we place special emphasis on the top-down information flow in which the system as a whole gains causal purchase over its components, This approach will reveal how the logical organization of biological replicators differs crucially from trivial replication associated with crystals (non-life). By addressing the causal role of information directly, many of the baffling qualities of life are explained.”
Nonlocal biological functions
“The most important features of biological information (i.e. functionality) are decisively nonlocal,” the authors say. “Biologically functional information is therefore not an additional quality, like electric charge, painted onto matter and passed on like a token. It is of course instantiated in biochemical structures, but one cannot point to any specific structure in isolation and say “Aha! Biological information is here!”
The authors expect that, by re-shaping the conceptual landscape in this fundamental way, not just the origin of life, but other major transitions will be explained — for example, the leap from single cells to multi-cellularity.
“In all of these cases where appeal is made to an informational narrative, we encounter context- (state-) dependent causation. In this respect, biological systems are quite unlike traditional mechanical systems evolving according to fixed laws of physics.
“In biological causation, subject to informational control and feedback, the dynamical rules will generally change with time in a manner that is both a function of the current state and the history of the organism (suggesting perhaps that even the concept of evolution itself may be in need of revision.”
Life in non-organic substrates?
This perspective “forces new thinking in how life might have arisen on a lifeless planet, by shifting emphasis to the origins of information control, rather than — for example — the onset of Darwinian evolution or the appearance of autocatalytic sets (i.e. either analog or digital that lack information control), which, although certainly important to the story of life’s emergence, do not rigorously define how/when life emerges as a function of chemical complexity.
“It also permits a broader view of life, where the same underlying principles would permit understanding of living systems instantiated in different chemical substrates (including potentially non-organic substrates). …
“Purely analog life-forms could have existed in the past but are not likely to survive over geological timescales without acquiring explicitly digitized informational protocols. Therefore life-forms that ‘go digital’ may be the only systems that survive in the long-run and are thus the only remaining product of the processes that led to life.
“As such, 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. This transition should be marked by a reversal in the causal flow of information from bottom-up only to a situation characterized by bi-directional causality.
“Characterizing the emergence of life as a shift in causal structure due to information gaining causal efficacy over matter marks the origin of life as a unique transition in the physical realm.”
Hallmarks of life
The authors suggest these specific hallmarks of life:
- Global organization
- Information as a causal agency
- Top-down causation
- Analog and digital information processing
- Laws and states co-evolve
- Logical structure of a universal constructor
- Dual hardware and software roles of genetic material
- Non-trivial replication
- Physical separation of instructions (algorithms) from the mechanism that implements them
Walker is also affiliated with the NASA Astrobiology Institute in Mountain View, Calif. and the Blue Marble Space Institute, Seattle.