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These are excerpts and elaborations from my book "The Nature of Consciousness"
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Hypercycles The German chemist Manfred
Eigenwas awarded the Nobel Prize in
1967 for discovering that very short pulses of energy could trigger extremely
fast chemical reactions. In the following years, he started looking for how
very fast reactions could be used to create and sustain life. Indirectly, he ended up
studying the behavior of biochemical
systems far from equilibrium. Eventually, Eigencame up with the concept
of an "hypercycle". A
hypercycle is a cyclic reaction network, i.e. a cycle of cycles of cycles (of
chemical reactions). Then he argued that life can be viewed as the product of a
hierarchy of such hypercycles. A catalyst is a substance
that favors a chemical reaction. When enough energy is provided, some catalytic
reactions tend to combine to form networks, and such networks may contain
closed loops, called catalytic cycles. If even more energy is
pumped in, the system moves even farther from equilibrium, and then catalytic
cycles tend to combine to form closed loops of a higher level, or hypercycles,
in which the enzymes produced by a cycle act as catalysts for the next cycle in
the loop. Each link of the loop is now a catalytic cycle itself. Eigenshowed that hypercycles are
capable of self-replication, which may therefore have been a property of nature
even before the invention of living organisms. Hypercycles are capable of
evolution through more and more complex stages. Hypercycles compete for natural
resources and are therefore subject to natural selection. The hypercycle falls short
of being a living system because it defines no "boundary": the
boundary is the container where the chemical reaction is occurring. A living
system, on the other hand, has a boundary that is part of the living system
(e.g., the skin). Catalysis is the phenomenon
by which a chemical reaction is sped up: without catalysis, all processes that
give rise to life would take a lot longer, and probably would not be fast
enough for life to happen. Then Eigenshows that they can be
organized into an autocatalytic cycle,
i.e. a cycle that is capable of self-reproducing: this is the fundamental
requirement of life. A set of autocatalytic cycles gets, in turn, organized
into a catalytic hypercycle. This catalytic hypercycle represents the basic
form of life. Formally:
"hypercycles" are a class of nonlinear reaction networks. They can
originate spontaneously within the population of a species through natural
selection and then evolve to higher complexity by allowing for the coherent
evolution of a set of functionally coupled self-replicating entities. A
hypercycle is based on nonlinear autocatalysis, which is a chain of
reproduction cycles, which are linked by cyclic catalysis, i.e. by another
autocatalysis. A hypercycle is a cycle of cycles of cycles. Eigens model explains the simultaneous unity (due to the use of a universal
genetic code) and diversity (due to the "trial and error" approach of
natural selection) in evolution. This dual process started even before life was
created. Evolution of species was
preceded by an analogous stepwise process of molecular evolution. Evolution itself turns out
to be inevitable: given a set of self-reproducing entities that feed on a
common and limited source of energetic/material supply, evolution will
spontaneously appear. Evolution is a direct consequence of the dynamics of
self-reproducing systems. That said, not all systems
are suitable for becoming successful biological systems. Systems can be
classified in four groups according to their stability with respect to
fluctuations: stable systems (the fluctuations are self-regulating),
indifferent systems (the fluctuations have no effect), unstable systems
(self-amplification of the fluctuations) and variable systems (which can be in
any of the previous states). Only the
last type is suitable for generation of biological information because it can
play all the best tactics: indifference towards a broad mutant spectrum,
stability towards selective advantages and instability towards unfavorable
configurations. In other words, it can take the most efficient stance in the
face of both favorable and adverse situations. Back to the beginning of the chapter "Self-organization and the Science of Emergence" | Back to the index of all chapters |
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