Network science to explain how molecular complexity appeared in space

O origin of chemical complexity in space is, in addition to an open question, a fundamental aspect to understand the first steps that gave rise to the origin of life. Now an international study, led by researchers at the Center for Astrobiology (CAB, CSIC-INTA), proposes a new approach to the origin of molecular complexity in space, making use of complex network theory.

The authors, who publish their work in the journal PNASexplain the appearance of complex molecules in the clouds of the interstellar medium from a new point of view: as an emergent process typical of the complexity theoryused in fields such as sociology and computing and which explains collective phenomena as diverse as traffic jams or avalanches.

The team created a theoretical and computational environment, called networldwhere the interaction between complex networks that can represent any simple structure, whether chemical, biological or social, is simulated.

The results show that, in ‘wild’ environments, only the simplest pieces of this type of LEGO are created. However, when the environment softens, these basic pieces actively interact, dramatically giving rise to an enormous diversity of compounds, which will later represent the fundamental building blocks of structures on a larger scale and in increasingly complex systems.

If we understand the nodes of our networks as atoms and each network as a molecule, NetWorld is able to describe the starting point in the origin of life process: the emergence of interstellar chemical complexity.

Jacobo Aguirre (CAB)

This system does not attempt to simulate the rules of real chemistry nor does it make use of real data, but as the lead author points out, James Aguirre from the CAB, “what is surprising is that if we understand the nodes of our networks as atoms and each network as a molecule, NetWorld is able to describe the starting point in the process of the origin of life: the emergence of complexity in evolution. of chemical diversity in the interstellar medium.

The connection between the extreme simplicity of the model and its ability to describe the real phenomenology of astrobiological relevancesuggests that many of the basic properties on the long road from space chemistry to prebiotic chemistry and ultimately to life as we know it may show simple, universal patterns.

NetWorld and Game Theory

The NetWorld environment models the evolution of complex network structures (nodes joined by connections) towards complexity. The rules of interaction between these networks, which allow them to grow and evolve, are very simple and were drawn from game theory: each node competes with the others to be well connected in the network as a result of the interaction.

So the rules have nothing to do with real chemistry or biology, but it’s a “network chemistry” abstract. NetWorld predicts a sharp transition from a simple “biodiversity” network (a few different networks of small size) to a much more complex one (thousands of different networks of very different size and complexity) when the parameter representing the environment reaches a critical value.

This transition is observed in different areas of astrobiology, so NetWorld is able to describe this fundamental property of the chemistry of the origin of life from a truly new point of view, the authors insist.

Similar astrophysical and computational environment

This is because in this astrophysical environment, the phenomenology is similar to that of the Networld computing environment: when interstellar clouds condense, interstellar dust protects the ultraviolet light that disrupts many chemical reactions, and the molecules created up to that moment interact, giving rise to dozens of molecules. new and much more complex.

“There is a drastic transition to complexity in the two systems, and the properties of these two transitions are equivalent,” says the co-author Fernando Puente Sanchesresearcher at the Swedish University of Agricultural Sciences.

According to the computational model, the abundance of structures that are created is proportional to the number of paths that give rise to each structure. so it was found proportional relationship hitherto unknown between the actual molecular abundances of the different molecules in dark clouds (such as hydrocyanic acid –HCN–, ammonia –NH3– and others) and the potential number of chemical reactions that generate them as a product.

Therefore, “NetWorld promises to be a new bridge between astrochemistry and complexity theory”, concludes the CAB astrochemist Izaskun Jiménez-Serraalso co-author of the article.