Network science to explain how molecular complexity arose in space

The origin of chemical complexity in space is, in addition to an open question, a fundamental aspect for understanding the first steps that led to the origin of life. Today, an international study, led by researchers from the Center for Astrobiology (CAB, CSIC-INTA), offers a new approach to the origin of molecular complexity in space, using complex network theory.

The authors, who publish their work in the journal PNAS, explain the appearance of complex molecules in the clouds of the interstellar medium from a novel point of view: as an emergent process typical of complexity theory, used in fields such as sociology and information technology and which explains collective phenomena as diverse as traffic jams or avalanches.

The team created a theoretical and computational environment, called NetWorld, where 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 building blocks actively interact, drastically giving rise to an enormous diversity of compounds, which would later represent the fundamental building blocks of structures on a larger scale and in increasingly larger systems. complex.

This system does not try to simulate the rules of real chemistry and does not use real data, but as lead author Jacobo Aguirre of CAB points out, “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 at the origin of the process of life: the emergence of complexity in the evolution of chemical diversity in the interstellar medium.

The link between the extreme simplicity of the model and its ability to describe true astrobiology-relevant phenomenology suggests that many of the fundamental properties of the long path that leads from space chemistry to prebiotic chemistry and ultimately to life as it is as we know it, could show simple and universal patterns.

NetWorld and game theory

The NetWorld environment models the evolution of complex network structures (nodes linked by connections) towards complexity. The rules of interaction between these networks, which allow them to grow and evolve, are very simple and have been taken from game theory: each node competes with the others to be well connected in the network thanks to the ‘interaction.

The rules therefore have nothing to do with real chemistry or biology, but rather an abstract “network chemistry”. NetWorld predicts an abrupt transition from a simple “biodiversity” network (a few different networks of small size) to a much more complex network (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 perspective, the authors insist.

Similar astrophysical and computing environment

Indeed, in this astrophysical environment, the phenomenology is similar to that of the Networld computing environment: when the interstellar clouds condense, the interstellar dust shields the ultraviolet light that hampers many chemical reactions, and the molecules created up at this time interact, giving rise to dozens of new, much more complex molecules.

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

According to the computer model, the abundance of structures created is proportional to the number of paths that give rise to each structure. Thus, a hitherto unknown proportional relationship was found between the actual molecular abundances of 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 CAB astrochemist Izaskun Jiménez-Serra, also a co-author of the paper.


M. García-Sánchez, J. Aguirre et al. “The emergence of interstellar molecular complexity explained by interacting networks”. ‘Proceedings of the National Academy of Sciences’ (PNAS), 2022.

Leave a Comment