University of Groningen
Enabling Darwinian evolution in chemical replicators
Mattia, Elio
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2017
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Mattia, E. (2017). Enabling Darwinian evolution in chemical replicators. Rijksuniversiteit Groningen.
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SUMMARY
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Self-replicating molecules are very likely to have played a central role in the origin of life from the so-called primordial soup. In this thesis, the mechanism of self-replication was studied in detail. The results in Chapter 2 show that the self-replicating molecules are capable of growing exponentially. This is a veryimportant breakthrough. Almost all self-replicating molecules discovered up to the latest years were not capable of exponential growth, due to the the fact that after a round of replication they remain bound to each other. The new replicators behave similarly, but in the form of fibres that break into smaller pieces upon simple mechanical agitation. Since the replication takes place at the extremities of the fibres, the breakage induces an exponential acceleration in the rate of replication. Exponential growth of replicators is important, since exponentially growing replicators are better prone to survive during Darwinian evolution. The fibres can be broken down in yet smaller molecules, after which the replication process can start again. This process is comparable with the constant arisal of new reproducing bacterial cells, while at the same time some of these bacteries die or get killed. Primordial molecular life was very likely the result of repeated attempts of replication in an environment where the replicators were repeatedly broken down, in a steady process or as a result of many destruction waves. After a number of attempts, thanks to replication errors, a replicator with a favourable mutation could appear. Due to this mutation, the replicator could be better at surviving the threats from its environment. This process is at the core of Darwinian evolution. In this research, the dynamics of a system where replication and destruction take place simultaneously were studied in detail in the lab and with the help of computer simulations. Based on these studies, presented in Chapter 3, it is in principle possible to set up an
experimental system where the replicators are constantly broken down into building blocks, from which new replicators can form. Energy-consuming, entropy-producing far-from-equilibrium replication conditions are necessary for Darwinian evolution. The simulations suggest that the energy coupling with a far-from-equilibrium replicating system is the most efficient when the replicators are destroyed selectively and sufficiently quickly to create a cycle of replication and destruction.
The research then focused on the development of replicators that compete with each other for their constituent building blocks. This competition yields the formation of replicators with mixed building blocks. Replication of nucleic acids (DNA, RNA) is based on information from the order of the individual nucleic acids. In the research described in Chapter 4 the pathways
by which information can be exchanged in peptide fibres were studied in detail. The results show that the exchange of building blocks from one fibre to another one takes place at the extremities thereof. Building blocks located in the core of a fibre are hardly used in the replication of other fibres. These building blocks are therefore protected from replication and the information that they carry can hardly be exchanged, unless the fibres continuously break in smaller pieces.
While in our experiments Darwinian evolution does not yet take place, we could observe in these systems a few processes of significance for Darwinian evolution: exponential growth of fibres, destruction of replicators and selective exchange of building blocks.
