The Changing View of Eukaryogenesis - Fossils, Cells, Lineages and How They All Come Together

Eukaryogenesis - the emergence of eukaryotic cells - represents a pivotal evolutionary event. With a fundamentally more complex cellular plan compared to prokaryotes, eukaryotes are major contributors to most aspects of life on Earth. For decades, we have understood that eukaryotic origins lie within both the Archaea domain and α-Proteobacteria. However, it is much less clear when, and from which precise ancestors, eukaryotes originated, or the order of emergence of distinctive eukaryotic cellular features. Many competing models for eukaryogenesis have been proposed, but until recently, the absence of discriminatory data meant that a consensus was elusive. Recent advances in paleogeology, phylogenetics, cell biology and microbial diversity, particularly the discovery of the 'Candidatus Lokiarcheaota' phylum, are now providing new insights into these aspects of eukaryogenesis. The new data have allowed the time frame during which eukaryogenesis occurred to be finessed, a more precise identification of the contributing lineages and the biological features of the contributors to be clarified. Considerable advances have now been used to pinpoint the prokaryotic origins of key eukaryotic cellular processes, such as intracellular compartmentalisation, with major implications for models of eukaryogenesis.