Nicholas Guttenberg

Bulk measurements of messy chemistries are needed for a theory of the origins of life

A feature of many of the chemical systems plausibly involved in the origins of terrestrial life is that they are complex and messy—producing a wide range of compounds via a wide range of mechanisms. However, the fundamental behaviour of such systems is currently not well understood; we do not have the tools to make statistical predictions about such complex chemical networks. This is, in part, due to a lack of quantitative data from which such a theory could be built; specifically, functional measurements of messy chemical systems. Here, we propose that the pantheon of experimental approaches to the origins of life should be expanded to include the study of ‘functional measurements’—the direct study of bulk properties of chemical systems and their interactions with other compounds, the formation of structures and other behaviours, even in cases where the precise composition and mechanisms are unknown. This article is part of the themed issue ‘Reconceptualizing the origins of life’.

Simple prebiotic synthesis of high diversity dynamic combinatorial polyester libraries

It is widely believed that the origin of life depended on environmentally driven complexification of abiotically produced organic compounds. Polymerization is one type of such complexification, and it may be important that many diverse polymer sequences be produced for the sake of selection. Not all compound classes are easily polymerized under the environmental conditions present on primitive planets, and it is possible that life’s origin was aided by other monomers besides those used in contemporary biochemistry. Here we show that alpha-hydroxy acids, which are plausibly abundant prebiotic monomers, can be oligomerized to generate vast, likely sequence-complete libraries, which are also stable for significant amounts of time. This occurs over a variety of reaction conditions (temperature, concentration, salinity, and presence of congeners) compatible with geochemical settings on the primitive Earth and other solar system environments. The high-sequence heterogeneity achievable with these compounds may be useful for scaffolding the origin of life.The origins of life likely involved abiotic combinatorial polymer synthesis but the characterisation of such mixtures is challenging. Here the authors show that large libraries of linear and cyclic oligomers spontaneously form from α-hydroxy acids under mild conditions which may be relevant to prebiotic synthesis.

Heredity in Messy ChemistriesHeredity in Messy Chemistries

For natural selection to progress, there must be a sufficiently large evolutionary space to explore. In systems with template-based replication, this space is combinatorially large in the length of the information-carrying molecules. Previous work has shown that it is also possible for heredity to occur in much less structured chemistries; this opens the question of how the structure of a reaction network relates to the number of heritable states it can support, and in particular, how the number of heritable states scales with system size for a given network topology. Answering this question would allow us to map out the space of possible chemical mechanisms for heredity, and to identify places where they might be found in the space of organic chemistries that might have been found on the early Earth. We show that by linearising around a fixed point in a chemical reaction network and solving the corresponding eigenvalue problem, it is possible to detect the set of independent autocatalytic subnetworks that can operate in the vicinity of that point. We investigate an upper bound on the scaling of the number of such “autocatalytic cores” with the number of distinct chemical species, and show that the number of cores scales at best as logN in the case of unstructured networks, but that adding a strong energy constraint on the network topology allows it to scale linearly, which is the best possible case.

Transferable Measurements of Heredity in Models of the Origins of Life

We propose a metric which can be used to compute the amount of heritable variation enabled by a given dynamical system. A distribution of selection pressures is used such that each pressure selects a particular fixed point via competitive exclusion in order to determine the corresponding distribution of potential fixed points in the population dynamics. This metric accurately detects the number of species present in artificially prepared test systems, and furthermore can correctly determine the number of heritable sets in clustered transition matrix models in which there are no clearly defined genomes. Finally, we apply our metric to the GARD model and show that it accurately reproduces prior measurements of the model’s heritability.