Journal of Molecular Evolution volume 89, pages 415–426 (2021 )Cite this article
We argue for multiple forms of life realized through multiple different historical pathways. From this perspective, there have been multiple origins of life on Earth—life is not a universal homology. By broadening the class of originations, we significantly expand the data set for searching for life. Through a computational analogy, the origin of life describes both the origin of hardware (physical substrate) and software (evolved function). Like all information-processing systems, adaptive systems possess a nested hierarchy of levels, a level of function optimization (e.g., fitness maximization), a level of constraints (e.g., energy requirements), and a level of materials (e.g., DNA or RNA genome and cells). The functions essential to life are realized by different substrates with different efficiencies. The functional level allows us to identify multiple origins of life by searching for key principles of optimization in different material form, including the prebiotic origin of proto-cells, the emergence of culture, economic, and legal institutions, and the reproduction of software agents.
An ongoing scientific challenge has been to create a general theory of life that integrates our empirical understanding of biology with logical principles that might transcend it (Cleland 2019; Goldenfeld and Woese 2011; Goldenfeld et al. 2017; Walker et al. 2017; Walker 2017; Davies and Walker 2016; Walker et al. 2018). The search for principles that are not dependent on evolved constraints and biochemical materials has been intriguing, but has not yet led to complete theories of how to identify, quantify, or create life (Langton 1984; von Neumann 1966; Langton et al. 1992, 1994; Küppers 1990; Yockey 2005; Walker and Davies 2013). Meeting this challenge would help to address several of the most interesting questions facing the natural sciences and biology in relation to questions of generality and universality. These would include the following: (1) how do biotic mechanisms emerge from abiotic ones, (2) how can we be sure that we have found life if it is materially different from life on Earth, and by extension, how do we verify that an environment is truly lifeless, for example, in a sample of ice from Enceladus?, and (3) how do we in general understand the range of possibilities for the origin and maintenance of life?