Review of hypotheses attempting to explain how and why eukaryotes originated from prokaryotic ancestors. Major theme is the exceptional nature and scale of the change, which lends weight from an evolutionary point of view to the notion that the Proterozoic Earth system must have in some way been “special” in terms of its disposition to produce evolutionary novelty. Discusses a “chicken and egg” problem, whereby respiratory electron transport in multiple mitochondria allows increased free energy availability per cell, which allows an energetically demanding cytoskeleton to be supported – but faces the issue that symbionts are difficult to acquire without phagocytosis, which requires a cytoskeleton in the first place. Suggests a “bottleneck” scenario, in which free living proto-eukaryotes are forced spatially/temporally together, may have increased the probability of endosymbiosis, potentially in connection with the Paleoproterozoic glaciation events.
(Boyle, R.A. “The problem of Eukaryotic origins in relation to the Early/Mid Proterozoic Earth system” Book Chapter, Revolutions in the Early Proterozoic: Tracking Geochemical and Geobiological Change, “Topics in Geobiology”, In Press.)