Peer-Reviewed Publications 

* Student Author, ** Postdoctoral Fellow Author  (Emergence@ASU members underlined)
  1. D. Gagler*, B. Karas*, C.P. Kempes, J. Malloy*, V. Mierzejewski*, A.D. Goldman, H. Kim**, S.I. Walker (2022) Scaling Laws in Enzyme Function Reveal a New Kind of Biochemical Universality. PNAS 119(9), e2106655119. [online]
  2. A. Frank, D. Grinspoon, S.I. Walker (2022) Intelligence as a Planetary Process. International Journal of Astrobiology. p 1-15. [online]
  3. J. Hanson*, S.I. Walker (2021) Formalizing falsification for theories of consciousness across computational hierarchies. Neuroscience of Consciousness 2021(2):niab014. [online]
  4. G. Valentini**, T.P. Pavlic, S.I. Walker, S.C. Pratt, D, Biro, T. Sasaki (2021) Naïve individuals promote collective exploration in homing pigeons eLife 2021;10:e68653. [online]
  5. H.B. Smith*, H. Kim**, S.I. Walker (2021). Scarcity of scale-free topology is universal across biochemical networks. Scientific Reports 11, 6542 [online]
  6. S. Marshal, C. Mathis, E. Carrick, G. Keenan, G.J.T. Cooper, H. Graham, M. Craven, P.S. Gromski, D.G. Moore**, S.I. Walker, L. Cronin (2021). Identifying molecules as biosignatures with assembly theory and mass spectrometry. Nature Communications 12, 3033 [online]
  7. H. Kim**, G. Valentini**, J. Hanson*, S.I. Walker (2021). Informational architecture across non-living and living collectives. Theory in Biosciences [online]
  8. T.P. Pavlic, J. Hanson*, G. Valentini**, S.I. Walker, S.C. Pratt (2021). Quorum sensing without deliberation: biological inspiration for externalizing computation to physical spaces in multi-robot systems. Swarm Intelligence 15, 171-203 ​[online]
  9. H.B. Smith*, A.Drew*, J. Malloy and S.I. Walker (2021). Seeding Biochemistry on Other Worlds: Enceladus as a Case Study. Astrobiology 21(2) [online]
  10.  J. Bell, G. Bianconi, D. Butler, J. Crowcoft, P.C.W. Davies, C. Hicks, H. Kim, I. Kiss, F. Di Lauro, C. Maple, A. Paul, M. Prokopenko, P. Tee, S.I. Walker (2021) Beyond COVID-19: Network science and sustainable exit strategies. J. Phys. Complexity, 2 021001 [online]
  11. G. Valentini**, N. Mizumoto, S.C. Pratt, T.P. Pavlic, S.I. Walker (2020). Revealing the structure of information flows discriminates similar animal social behaviors. ELife, 2020;9:e55395. [online]
  12. D.M. Glaser, H.E. Hartnett, S.J. Desch, C.T. Unterborn, A. Anbar, S. Buessecker, T. Fisher*, S. Glaser, S.R. Kane, C.M. Lisse, C. Millsaps*, S. Neuer, J.G. O'Rourke, N. Santos, S.I. Walker, and M. Zolotov (2020) Detectability of Life Using Oxygen on Pelagic Planets and Water Worlds. The Astrophysical Journal 893 163. [online]
  13. G. Valentini**, N. Masuda, Z. Shaffer, J.R. Hanson*, T. Sasaki, S.I. Walker, T.P. Pavlic, S.C. Pratt. (2020) Division of labour promotes the spread of information in colony emigrations by the ant Temnothorax rugatulus. Proceedings of the Royal Society B. 287(1924):20192950. [online]
  14. E. Borriello**, S.I. Walker, M.D. Laubichler. (2020) Cell phenotypes as macrostates of the GRN dynamics. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution.  [online]
  15. A. Truitt, P. Young, S.I.Walker, A. Spacek (2020)  A Flexible Bayesian Framework for Assessing Habitability with Joint Observational and Model Constraints. [Preprint] The Astronomical Journal 159(2), 55. [online]
  16. J. Hanson* and S.I. Walker (2019) Integrated Information and Feed-forward Philosophical Zombies. Entropy 21(11), 1073. [online]
  17. D. Moore** and S.I. Walker (2019) Inferring a Graph’s Topology from Games Played on It. Proceedings ALIFE 2019: The 2019 Conference on Artificial Life, pp. 271–277. [online]
  18. S.I.Walker (2019) The new physics needed to probe the origins of life. Nature 569, 36-38. [online]
  19. A.J. Surman, M. Rodriguez-Garcia, Y.M. Abul-Haija, G.J.T. Cooper, P.S. Gromski, R. Turk-MacLeod, M. Mullin, C. Mathis*, S.I Walker and L. Cronin (2019) Environmental control programs the emergence of distinct functional ensembles from unconstrained chemical reactions. Proceedings of the National Academy of Sciences 116, no. 12: 5387-5392. [online]
  20. H. Kim**, H.B. Smith*, C. Mathis*, J. Raymond and S.I. Walker (2019) Universal scaling across biochemical networks on Earth. Science Advances 5: eaau0149. [online]
  21. B. Daniels, H. Kim**, D. Moore**, S. Zhou*, H.B. Smith*, B. Karas*, S.A. Kauffman, and S.I. Walker (2018) Criticality Distinguishes the Ensemble of Biological Regulatory Networks Phys. Rev. Lett. 121, 138102. [online]                     
  22. D. Moore**, G.Valentini**, S.I. Walker and M. Levin (2018) Inform: Efficient Information-theoretic Analysis of Collective Behaviors. Frontiers in Robotics and AI. doi: 10.3389/frobt.2018.00060
  23. G.Valentini**, D.Moore**, J.Hanson*, T.P. Pavlic, S. Pratt and S.I Walker (2018) Transfer of Information in Collective Decisions by Artificial Agents. Proceedings of ALIFE 2018: The 2018 Conference on Artificial Life, pp. 641–648. [online]
  24. S.I. Walker, W. Bains, L. Cronin, S. DasSarma, S. Danielache, S. Domagal-Goldman, B. Kacar, N.Y. Kiang, A. Lenardic, C.T. Reinhard, W. Moore, E. Schwieterman, E. Shkolnik and H.B. Smith* (2018) Exoplanet biosignatures: future directions. Astrobiology, 18(6), pp.779-824. https://doi.org/10.1089/ast.2017.1738 
  25. N.Y. Kiang, S. Domagal-Goldman, D.C. Catling, Y. Fuji, V.S. Meadows, E. Schwieterman and S.I. Walker (2018) Exoplanet Biosignatures: At the Dawn of a New Era of Planetary Observations. Astrobiology 18(6) 619-629  http://doi.org/10.1089/ast.2018.1862
  26. E.W. Schwieterman, N.Y. Kiang, M.N. Parenteau, C.E. Harman, S. DasSarma , T.M. Fisher*, G.N. Arney, H.E. Hartnett, C.T. Reinhard, S.L. Olson, V.S. Meadows, C.S. Cockell, S.I. Walker, J.L. Grenfell, S. Hegde, S. Rugheimer, R. Hu, and T. W. Lyons (2018) Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life. Astrobiology 18(6): 663 - 708 http://doi.org/10.1089/ast.2017.1729
  27. S.I. Walker, N. Packard and G. Cody (2017) Re-Conceptualizing the Origin of Life. Phil. Trans. Roy. Soc. A.  375:20160337 [online]
  28. W. Marshall, H. Kim**, S.I. Walker, G. Tononi, and L. Albantakis (2017) How Causal Analysis Can Reveal Autonomy in Models of Biological Systems. Phil. Trans. Roy. Soc. A.  375:20160358 ​  [online]
  29. C. Mathis*, S. Ramprasad, S.I. Walker, and N. Lehman (2017) Prebiotic RNA Network Formation: A Taxonomy of Molecular Cooperation. Life 7(4):38. [online]
  30. E. Borriello** and S.I. Walker (2017) An Information Theoretic Classification of Elementary Cellular Automata. Complexity. Article ID 1280351. [online] [preprint]
  31. D. Moore**,  S.I. Walker, and M. Levin (2017) Cancer as a Disorder of Patterning Information: computational and biophysical perspectives on the cancer problem. Convergent Science Physical Oncology. 3(4): 043001. [online]
  32. A. Adams*, A. Berner*, P.C.W. Davies and S.I. Walker (2017) Physical Universality, State-Dependent Dynamics and Open-Ended Evolution. Entropy. 19(9): 461.  [online]  (cover article)
  33. S.I. Walker (2017) Origins of Life: A Problem for Physics, A Key Issues Review. Reports on Progress in Physics.  80(9): 092601 [online] arxiv:1705.08073
  34. A. Adams* and S.I.Walker (2017) Real-world Open-ended Evolution: A League Of Legends Adventure. International Journal of Design & Nature and Ecodynamics 12: 458-469.
  35. A. Adams*, H. Zenil, P.C.W. Davies and S.I.Walker (2017) Formal Definitions of Unbounded Evolution and Innovation Reveal Universal Mechanisms for Open-Ended Evolution in Dynamical Systems. Scientific Reports. 7: 997. ​[preprint] arxiv:1607.01750 [online]
  36. C. Mathis*, T. Bhattacharya and S.I. Walker (2017) The Emergence of Life as a First Order Phase Transition. Astrobiology 17(3): 266-276. [online] [preprint] 
  37. ​P.C.W. Davies and S.I. Walker (2016) The Hidden Simplicity of Biology: A Key Issues Review. Rep. Prog. Phys. 79(10) 102601.
  38. ​Domagal-Goldman and Wright et al. (includes S.I. Walker ​and 45 others) (2016) Astrobiology Primer 2.0. Astrobiology 16(8):561-653. [online]
  39. L. Cronin and S.I. Walker (2016) Beyond Prebiotic Chemistry. Science 352: 1174-1175. DOI:10.1126/science.aaf6310 [online]
  40. S.I. Walker, H. Kim** and P.C.W. Davies (2016) The Informational Architecture of the Cell. Phil Trans A. 2016 374 20150057; DOI: 10.1098/rsta.2015.0057 [online]
  41. H. Kim**, P.C.W. Davies and S.I. Walker (2015) New Scaling Relation for Information Transfer in Biological Networks. J. Roy. Soc. Interface 12 20150944; DOI: 10.1098/rsif.2015.0944 [online]
  42. P. Nghe, W. Hordijk, S. Kauffman, S.I. Walker, F. Schmidt, H. Kemble, J.A.M. Yeates and N. Lehman (2015) Prebiotic Network Evolution: Six Key Parameters. Roy. Soc. Chem. Mol. Biosyst. 11, 3206-3217 [online]
  43. S.I. Walker (2014) Top-down causation and the rise of information in the Emergence of Life. Information 5, 424-439. [online]
  44. T.Pavlic, A.M. Adams*, P.C.W. Davies and S.I. Walker (2014) Self-referencing cellular automata: A model of the evolution of information control in biological systems. In Proc. Artificial Life XIV arXiv:1405.4070 [online]
  45. S.I. Walker, P.C.W. Davies, P. Samantray* and Y. Aharanov (2014) Quantum Non-Barking Dogs. New J. Phys 16: 063026. [online]  
  46. S.I. Walker and P.C.W. Davies (2013) The Algorithmic Origins of Life.  J. Roy. Soc. Interface 6:20120869  [online] preprint: arXiv:1207.4803
  47. S.I. Walker, B. Callahan, G. Arya, J.D. Barry, T. Bhattacharya, S. Grigoryev, M. Pellegrini, K. Rippe, S.M. Rosenberg (2013) Evolutionary Dynamics and Information Hierarchies in Biological Systems. Annals. N.Y. Acad. Sci. USA. [online]
  48. N. Vaiyda, S.I. Walker and N. Lehman (2013) Recycling of Informational Units Leads to Selection of Replicators in a Prebiotic Soup. Chemistry & Biology 20: 241 – 252. [online]
  49. M. Gleiser and S.I. Walker (2012) Life’s Chirality from Prebiotic Environments. Int. J. Astrobio. 11: 287- 296.  [online]  preprint: arXiv:1202.5048
  50. M. Wu, S.I. Walker and P.G. Higgs (2012) Autocatalytic Replication and Homochirality in Biopolymers: Is Homochirality a Requirement of Life or a Result of It? Astrobiology 12: 809 – 817. [online]
  51. S.I. Walker, L. Cisneros and P.C.W. Davies (2012) Evolutionary Transitions and Top-Down Causation. Proceedings of Artificial Life XIII. 283-290 [online] preprint: arXiv:1207.4808
  52. S.I. Walker, M.A. Grover and N. V. Hud (2012) Universal Sequence Replication, Reversible Polymerization and Early Functional Biopolymers: A Model for the Initiation of Prebiotic Sequence Evolution. PLoS ONE 7 (4):  e34166. [online] 
  53. D. Schulze-Makuch, P.C.W. Davies and S.I. Walker (2012) A Series of One-Way Missions to Explore and Colonize Mars.Proceedings of the 2012 Global Space Exploration Conference. 
  54. M. Gleiser, B. Nelson and S.I. Walker (2012) Chiral Polymerization in Open Systems From Chiral-Selective Reaction Rates.  Orig. Life Evol. Biosph. 42: 333-346. [online]
  55. S.I. Walker (2011) Homochirality, In Encyclopedia of Astrobiology. M. Gargaud (ed.)
  56. M. Gleiser and S.I. Walker (2010) The  Chirality of Life: From Phase Transitions to Astrobiology.  Astronomy and Relativistic Astrophysics: New Phenomena and New States of Matter in the Universe Proceedings of the Third Workshop (IWARA07). 17 – 30.  preprint: arXiv:0811.1291 [online]
  57. M. Gleiser and S.I. Walker (2009) Toward Homochiral Protocells in Noncatalytic Peptide Systems. Orig. Life Evol Biosph.39: 479-493.  [online]
  58. M. Gleiser, J. Thorarinson and S.I. Walker (2008) Punctuated Chirality. Orig. Life Evol Biosph. 38: 499-508.  [online]
  59. M. Gleiser and S.I. Walker (2008) An extended model for the evolution of prebiotic homochirality: A bottom-up approach to the origins of life. Orig. Life Evol. Biosph. 38: 293 – 315. [online]

Book Chapters, Reports

*Essay contest award winning
  1. ​S.I. Walker and C. Mathis*. Network Theory in Prebiotic Evolution. Prebiotic Chemistry and Chemical Evolution of the Nucleic Acids. C.A. Menor Salvan (ed.) Springer Publishing, 2018. [online]
  2. *​S.I. Walker. Bio from Bit. Wandering Towards a Goal A. Aguirre, B. Foster and Z. Merali (ed.) Springer, 2018. [online] [Essay awarded Fourth Prize in 2017 Foundational Questions in Science Institute Essay Contest - original essay available here] 
  3. S.I.Walker, P.C.W. Davies, and G.F.R. Ellis  (eds.) From Matter to Life: Information and Causality. Cambridge University Press 2017. 
  4. S.I.Walker and P.C.W. Davies. The "Hard Problem" of Life. In From Matter to Life: Information and Causality. S.I. Walker, P.C.W. Davies and G.F.R. Ellis (eds). Cambridge University Press 2017.  [preprint]
  5. S.I. Walker More is Not Just Different, its Causal. In Ahead of the Curve: Hidden breakthroughs in the biosciences. M. Levin and D. Adams (eds) IOP Publishing, Bristol UK, 2017. 
  6. ​S.I.Walker and P.C.W. Davies. From the Origins of Life to the Nature of Intelligence. To appear in Complexity and Society. Princeton University Press.
  7. *​S.I. Walker. The Descent of Math. In Trick of Truth: The Mysterious Connection Between Physics and Mathematics? A. Aguirre, B. Foster and Z. Merali (ed.) Springer, 2016. [online] [Essay awarded "Out-of the-box-thinking" Prize in 2015 Foundational Questions in Science Institute Essay Contest - original essay available here] 
  8. *S.I. Walker. Is Life Fundamental? In Questioning the Foundations of Physics: Which of our Fundamental Assumptions are Wrong? Anthony Aguirre, Brendan Foster, Zeeya Merali (Eds.) 2015 Springer [online]  [Essay awarded 4th prize in 2013 Foundational Questions in Science Institute Essay Contest - original essay available here]
  9. C. Burrows, S.I. Walker, S. Amin and E.V. Armburst. Alternative Chemistries for Life: Empirical Approaches. A NSF/NASA Report, J.T. Goodwin and D.G. Lynn (eds). 2014 [online]
  10. S.I. Walker. Transition from Abiotic to Biotic: Is There an Algorithm for It? In Astrobiology: An Evolutionary Approach. Vera Kolb ed. 2014 CRC Press. [online]

Popular Writing

  1. M. Lachmann and S.I. Walker (2019) Alive does not equal Life. Aeon Magazine [online]
  2. S.I. Walker (2017) The Origin and Nature of Life on Earth: The Emergence of the Fourth Geosphere (Review) Physics Today 70, no. 9: 58-58. [online]
  3. S.I. Walker The New Science of Astrobiology. Visions, Ventures, Escape Velocities: A Collection of Space Futures. E. Finn, J. Eschrich, and J. Ulman (eds). Center for Science and the Imagination, Arizona State University. [online]
  4. S.I. Walker It from Vital Bit. The Rightful Place of Science: Frankenstein. M.K. Halpern, J. Sadowski, and J. Eschrich (eds). Consortium for Science, Policy, Outcomes [online]
  5. S.I. Walker (2014) Little Green Men Might Not Be So ”Green”, Slate FutureTense [online]