Great Oxidation Event
Origin of eukaryotes

It has been proposed that a local rise in oxygen levels due to cyanobacterial photosynthesis in ancient microenvironments was highly toxic to the surrounding biota, and that this selective pressure drove the evolutionary transformation of an archaeal lineage into the first eukaryotes. Oxidative stress involving production of reactive oxygen species (ROS) might have acted in synergy with other environmental stresses (such as ultraviolet radiation and/or desiccation) to drive selection in an early archaeal lineage towards eukaryosis. This archaeal ancestor may already have had DNA repair mechanisms based on DNA pairing and recombination, and possibly some kind of cell fusion mechanism. The detrimental effects of internal ROS (produced by endosymbiont proto- mitochondria) on the archaeal genome could have promoted the evolution of meiotic sex from these humble beginnings. Selective pressure for efficient DNA repair of oxidative DNA damage may have driven the evolution of eukaryotic sex involving such features as cell-cell fusions, cytoskeleton-mediated chromosome movements and emergence of the nuclear membrane. Thus the evolution of eukaryotic sex and eukaryogenesis were likely inseparable processes that evolved in large part to facilitate DNA repair. The evolution of mitochondria, which are well suited for oxygenated environments, may have occurred during the GOE.

However, other authors express scepticism that the GOE resulted in widespread eukaryotic diversification due to the lack of robust evidence, concluding that the oxygenation of the oceans and atmosphere does not necessarily lead to increases in ecological and physiological diversity.
combination:two_responses