What is Life?: How Chemistry Becomes Biology (Oxford Landmark Science)

by Addy Pross

cooperation is endemic in the biological world—biologists call it symbiosis.

the entire process when viewed over an evolutionary time frame is seen to be one of complexification. The main difference between the two phases is that the first phase, the chemical phase, is the low-complexity phase, while the second phase, the so-called biological phase is the high-complexity phase, all taking place within the context of replicating entities.

complexification, primarily through network establishment, appears to be the mechanism for the transformation of simpler chemical replicators into more complex biological ones. In

replication, mutation, complexification, selection, evolution

The previous discussion might suggest that the evolutionary process is based solely on complexification and this is clearly not the case. It is well established that in particular instances evolution follows a process of simplification.

the processes of abiogenesis and evolution are actually one single physicochemical process governed by one single mechanism, rather than two discrete processes governed by two different mechanisms.

Phenomena at a higher hierarchical level of complexity are normally explained in terms of scientific principles associated with a lower hierarchical level. Thus we conventionally explain biological phenomena in chemical terms and chemical phenomena in physical terms,

the faster replicating molecule will out-replicate the slower replicating molecule and drive it to extinction.

natural selection = kinetic selection Biological natural selection merely emulates chemical kinetic selection. Natural selection is the biological term, kinetic selection is the chemical term.

fitness = dynamic kinetic stability (DKS)

in order to understand life’s essence one should focus on life’s population aspect, not its individual aspect. Life is an evolutionary phenomenon and evolution does not operate on individuals, only on populations.

the population of replicating RNAs that is generated by this exploration of the fitness landscape does not consist of one single sequence, but rather a population of RNAs of differing sequences, centred around the most successful sequence (termed the wild type) within that population.

This population of varied sequences was termed a quasispecies,

in the RNA sequences that it is not the fittest sequence that is selected for but the fittest population of sequences—the fittest quasispecies—that is selected

heterogeneous populations evolve more effectively than homogeneous ones.

the essence of stability in the world of replicators is rooted in populations, not individuals.

evolution operates so that DKS tends to increase over time.

the relative rates at which the two RNAs replicate may be taken as a quantitative measure of the relative DKSs of the two RNA populations.

DKS for populations of RNAs is circumstantial. Its magnitude depends on the particular materials that are present in the reaction.

Thermodynamic stability is an intrinsic property of any system and is measured in closed systems. Dynamic kinetic stability depends on rates of reaction, is highly sensitive to reaction conditions, and can only be assessed in open systems, in which energy and resources are continually supplied.

two crude measures of DKS are actually available. These are the steady-state population number for a given replicating entity and the length of time that the replicating population has managed to maintain itself. A large steady-state population of some life form means that it is more readily able to withstand environmental changes that may undermine its existence.

fitness is the biological expression of a particular kind of stability

the driving force for all chemical reactions is just the omnipresent Second Law of Thermodynamics.

Forces do not have to be visible to be identified. The existence of a force is postulated through empirical recognition of its action. In the case of replicating systems and their clear tendency to become transformed into more effective replicating systems, the driving force can now be identified as the drive toward greater DKS.