Direction, agency and function in the evolution of symbiotic integration

Symbiosis and the evolution of interdependencies among organisms, has underpinned some of the most fundamental transitions in the history of life, from the origin of eukaryotic cells to the evolution of the photosynthetic plants and algae that dominate global carbon cycling. Currently, each of these symbioses is treated as a singularity, precluding a process-based understanding of the underlying evolutionary drivers. Our project will integrate phylogenetics, comparative genomics, theoretical biology and philosophy to test whether these disparate cases of symbiosis share a common underlying process, and if so whether this process imbues evolution with direction, leading to fundamental transformations in individuality and rearrangements of organismal agency. Combining analyses of known and new host-symbiont systems that we will identify across the tree of life, we will determine the extent to which the evolution of symbiosis is a directional process, channelling organisms towards a tightly integrated fate. We will also investigate how the individuality of the symbionts was modified as they became more tightly integrated and how this process affected their agency and that of the newly emerging symbiont. Our work will answer these questions, delivering the first empirical results on the genomic basis of directionality in evolution, and the first comparative analysis of how this might have affected organismal agency. The broader impact of the project will be to establish a new, empirically-grounded philosophical framework for understanding the evolution of symbiotic interactions across the tree of life that will enable insights to be shared among different model systems and research fields, guide the study of new cases, and provide fundamental new insights into directionality and agency in evolution.