 Animals such as ourselves could not live without oxygen, which is a powerful electron acceptor that allows the energy investments permissive of large animal body size (Payne et al. 2011). Oxygen on this planet would not have become available were it not for pioneering oxygen-producing microbes, which are photosynthesizers called cyanobacteria. They not only began to excrete oxygen almost three billion years ago, but their very capacity to do so was forcibly captured by later eukaryotes and eventually led to algae, plants, and the planet we know today. In a distal causal sense, therefore, philosophy is possible because of bacterial photosynthesis.