The evolutionary origins of hydrogenosomes have been the subject of considerable debate. From early days it was apparent that hydrogenosomes had evolved on multiple occasions in different eukaryotes, but from which progenitor organelle or endosymbiont was unresolved. It is already apparent from the contributions to this volume, that identifying the genetic contribution to eukaryotes of the mitochondrial endosymbiosis, and revealing the functions of its descendent organelles, are key to understanding eukaryotic biology and evolution. This book closes the gap between the endosymbiotic theory for the origin of organelles and their incorporation into evolutionary theory.
