The endomembrane system: establishment, elaboration, and sculpting across evolutionary time. Top: cellular configuration of intracellular membrane architectural features. Second from top: molecular machineries that are associated with the endomembrane system, and predicted points of origin in eukaryotic evolution. Third from top: diagrams of cellular architectures to illustrate the origins of phagocytosis, internal membranes, and endosymbiotic organelles, and how these relate to the origins of cellular systems and the first (FECA) and last (LECA) eukaryotic common ancestors. The suggested sequence of events, although being the one that we favor, is not the only possible order; it is still unresolved at which points the nucleus, flagellum, mitochondria, phagocytosis, and endocytosis developed. Bottom: category of cell, using a generalized terminology.