From astrochemistry to life: network theory reveals universal patterns in the appearance of complex systems

The origin of chemical complexity in space is, in addition to an open question, a fundamental aspect to understand the first steps of the origin of life.

A recent study proposes a new approach to the origin of molecular complexity in space using the theory of complex networks.

The study has been led by the Center for Astrobiology (CAB), dependent on the Higher Council for Scientific Research (CSIC) and the National Institute for Aerospace Technology (INTA), all of these entities in Spain.

The authors of the study explain the appearance of complex molecules in the clouds of the interstellar medium from a novel point of view: chemical complexity arises as an emergent process typical of complexity theory, a discipline that explains collective phenomena as diverse as traffic jams or the avalanches.

These researchers have created a theoretical and computational environment, called NetWorld, where the interaction between complex networks that can represent any simple structure, be it chemical, biological or social, is simulated. The work presented shows that, in “wild” environments, only the simplest pieces of “LEGO” are created. However, when the environment softens, these basic pieces actively interact, drastically giving rise to an enormous diversity of compounds that will later represent the fundamental bricks of structures on a larger scale and in increasingly complex systems.

According to its main author, Jacobo Aguirre, from the group of Prebiotic Chemistry and Physics of Complex Systems of the Department of Molecular Evolution of the Center for Astrobiology (CAB): “What is surprising is that, although our system does not try to simulate the rules of real chemistry nor does it make use of real data, if we understand the nodes of our networks as atoms and each network as a molecule, the theoretical and computational framework that we have developed (NetWorld) is capable of describing the starting point in the process of the origin of life : the emergence of complexity in the evolution of chemical diversity in the interstellar medium”.

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

Artist’s rendering of the connection created between the science of complex networks and astrochemistry that the authors of this study introduce to explain the emergence of chemical complexity in space. (Image: PNAS / Marina Fernández-Ruz (CAB), CSIC-INTA)

NetWorld and its applications to real data

The NetWorld environment models the evolution of complex network-like structures (ie, nodes joined by connections) toward complexity. The rules of interaction between these networks, which allow them to grow and evolve, are very simple and have been extracted from game theory: each node competes with the rest to be well connected in the network as a result of the interaction. Therefore, the rules have nothing to do with real chemistry or biology, but rather an abstract “network chemistry”.

In this way, NetWorld predicts a drastic transition from a simple network “biodiversity” (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. And 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 novel point of view. This is because in this astrophysical environment the phenomenology is similar to that of the NetWorld computational environment: when interstellar clouds condense, interstellar dust shields ultraviolet light that hinders many chemical reactions, and the molecules created up to that moment interact giving give rise to dozens of new, much more complex molecules. “There is a drastic transition towards complexity in the two systems, and the properties of these two transitions are equivalent,” says Fernando Puente-Sánchez, a researcher at the Swedish University of Agricultural Sciences and co-author of the study.

a new perspective

Models often allow us to look at reality from new perspectives. The results obtained with NetWorld made the team look at the real abundance data of the molecules detected in the interstellar medium from a new perspective, since, in this computational model, the abundance of the structures that are created is proportional to the number of paths that give rise to each structure. Encouraged by this result, the team has found a hitherto unknown proportional relationship between the actual molecular abundances of the various molecules in the dark clouds (such as HCN, NH3, etc.) 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 astrochemist Izaskun Jiménez-Serra, co-author of the study.

The study is entitled “The emergence of interstellar molecular complexity explained by interacting networks”. And it has been published in the academic journal Proceedings of the National Academy of Sciences (PNAS). (Source: CAB)