Orig Life Evol Biosph (2010) 40:119–120 DOI 10.1007/s11084-010-9189-y EDITORIAL NOTE Defining Life: Conference Proceedings Jean Gayon & Christophe Malaterre & Michel Morange & Florence Raulin-Cerceau & Stéphane Tirard Received: 14 September 2009 /Accepted: 15 September 2009 / Published online: 5 March 2010 # Springer Science+Business Media B.V. 2010 Keywords Definition of life . History of science . Origin of life . Philosophy of science Foreword This Special Issue of Origins of Life and Evolution of Biospheres contains papers based on the contributions presented at the Conference “Defining Life” held in Paris (France) on 4–5 February, 2008. The main objective of this Conference was to confront speakers from several disciplines—chemists, biochemists, biologists, exo/astrobiologists, computer scientists, philosophers and historians of science—on the topic of the definition of life. Different viewpoints of the problem approached from different perspectives have been expounded and, as a result, common grounds as well as remaining diverging arguments have been J. Gayon Institut d’Histoire et de Philosophie des Sciences et des Techniques, Université Paris 1 - Panthéon Sorbonne, 13 rue du Four, 75006 Paris, France e-mail: [email protected] C. Malaterre Institut d’Histoire et de Philosophie des Sciences et Techniques, Université Paris 1 - Panthéon Sorbonne, 13 rue du Four, 75006 Paris, France e-mail: [email protected] M. Morange Centre Cavaillès and IHPST, Ecole Normale Supérieure, 29 rue d’Ulm, 75230 Paris Cedex 05, France e-mail: [email protected] F. Raulin-Cerceau (*) Centre A. Koyré, Muséum National d’Histoire Naturelle, 57 rue Cuvier, 75005 Paris, France e-mail: [email protected] S. Tirard Université de Nantes, Centre François Viète d’Histoire des Sciences et des Techniques, 2 rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France e-mail: [email protected] 120 J. Gayon et al. identified. In addition to individual talks, two large roundtables gave ample room for speakers to discuss their diverging viewpoints. This volume collects almost all the contributions presented during the Conference and provides a rich spectrum of renewed answers to the ever-standing question “What is Life?”. Besides the arguments directly regarding this question, more philosophical or historical reflections are also proposed in this issue that were not presented during the Conference. This volume also offers a synthesis written by J. Gayon taking each contribution into account. To conclude this foreword, we would like to thank all the participants and speakers who made this Conference a most stimulating event. Each provided novel ideas to “Defining Life” while highlighting the extreme difficulty to reach a consensus on this topic. We are also very grateful to the French CNRS Interdisciplinary Program Origines des Planètes et de la Vie (Origins of Planets and Life) for its generous support, as well as to the National Museum of Natural History in Paris for hosting the Conference. We also thank Alan W. Schwartz for generously offering this space for publishing the Proceedings of the Conference. Orig Life Evol Biosph (2010) 40:121–130 DOI 10.1007/s11084-010-9190-5 DEFINING LIFE Software Replica of Minimal Living Processes Hugues Bersini Received: 4 January 2009 /Accepted: 21 April 2009 / Published online: 5 March 2010 # Springer Science+Business Media B.V. 2010 Abstract There is a long tradition of software simulations in theoretical biology to complement pure analytical mathematics which are often limited to reproduce and understand the self-organization phenomena resulting from the non-linear and spatially grounded interactions of the huge number of diverse biological objects. Since John Von Neumann and Alan Turing pioneering works on self-replication and morphogenesis, proponents of artificial life have chosen to resolutely neglecting a lot of materialistic and quantitative information deemed not indispensable and have focused on the rule-based mechanisms making life possible, supposedly neutral with respect to their underlying material embodiment. Minimal life begins at the intersection of a series of processes which need to be isolated, differentiated and duplicated as such in computers. Only software developments and running make possible to understand the way these processes are intimately interconnected in order for life to appear at the crossroad. In this paper, I will attempt to set out the history of life as the disciples of artificial life understand it, by placing these different lessons on a temporal and causal axis, showing which one is indispensable to the appearance of the next and how does it connect to the next. I will discuss the task of artificial life as setting up experimental software platforms where these different lessons, whether taken in isolation or together, are tested, simulated, and, more systematically, analyzed. I will sketch some of these existing software platforms: chemical reaction networks, Varela’s autopoietic cellular automata, Ganti’s chemoton model, whose running delivers interesting take home messages to open-minded biologists. Keywords Artificial life . Autopoiesis . Chemoton . Computer simulations Introduction to Artificial Life Proponents of artificial life have chosen to resolutely neglecting a lot of materialistic and quantitative information deemed not indispensable to focus on the rule-based mechanisms H. Bersini (*) IRI DIA–ULB, CP 194/6, 50, av. Franklin Roosevelt, 1050 Bruxelles, Belgium e-mail: [email protected] 122 H. Bersini making life possible, supposedly neutral with respect to their underlying material embodiment, and to replicate them in a non-biochemical substrate. In artificial life, the importance of the substrate is purposefully understated for the benefit of the function (software should “supervene” to an infinite variety of possible hardware). Minimal life begins at the intersection of a series of processes which need to be isolated, differentiated and duplicated as such in computers. Only software development and running make possible to understand the way these processes are intimately interconnected in order for life to appear at the crossroad. Artificial life obviously relates to exobiology since the later cannot restrict itself to a mere materialistic view of life in order to detect it elsewhere. The material substrate could be something totally different and the presence of life must be suspected through its functions, much before being able to dissect it. Artificial life does not attempt to provide an extra thousandth attempt definition of life, any more than do most biologists. “Defining” is a sociological endeavor which consists in grounding something semantically rather weak on a stronger semantic support. The rejection of an authoritative definition of “life” is often compensated for by a list of functional properties which never finds unanimity amongst its authors. Some demand more properties, others require fewer of those properties that are often expressed in terms of a vague expression such as “self- maintenance”, “self-organization”, “metabolism”, “autonomy”, “self-replication”, “open- ended evolution”. A first determining role of artificial life consists in the writing and implementing of software versions of these properties and of the way they do connect, so as to disambiguate them, making them algorithmically precise enough that, at the end, the only reason for disagreement on the definition of life would lie in the length or the composition of this list and on none of its items. Beginning at the next chapter, I will sketch the history of life as the disciples of artificial life understand it, by placing these different lessons on a temporal and causal axis, showing which one is indispensable to the appearance of the next and how does it connect to the next. The task of artificial life is to set up experimental software platforms where these different lessons, whether taken in isolation or together, are tested, simulated, and, more systematically, analyzed. I will outline some of these existing software platforms whose running delivers interesting take home messages to open-minded biologists. The History of Life Seen by Artificial Life Appearance of Chemical Reaction Cycles and Autocatalytic Networks In order for a system to emerge and maintain itself inside a soup of molecules which are potentially reactive and contain very varied constituents (which could correspond to the initial conditions required for life to appear i.e. the primordial soup), this reactive system must form an internally cycled network or a closed organisation, in which every molecule is consumed and produced back by the network. A network of this kind will be materially closed but energetically open if none of the molecules appears in or disappears from the network as a result of external factors, whereas energy, originating in external sources, is necessary for the reactions to start and take place. The presence of such a energy flux, maintaining the network far from the thermodynamic equilibrium, is needed since, without it, no reactive flow would be possible circulating through the entire network. A reaction cycle thus acts as a chemical machine, energetically driven from the outside. The network transforms as much as it “keeps on” all the chemical agents which it recruits. Biologists generally agree that a reactive network must exist prior to the appearance of life, at least to Software Replica of Minimal Living Processes 123 catalyze and make possible the