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Clearly, eukaryotic history goes back far into the era when the earth's atmosphere contained little or no oxygen, well over two billion years ago. Our current concept of the origin of the eukaryotic cell is in flux, however, and an evolutionary sequence that appears simple when conceptualized on a phylogenetic tree diagram may be far more complex and interesting in reality. We know that the eukaryotic cell is of ancient origin, but we do not yet know the evolutionary dynamic that underlies its formation.
Eukaryotic cells originated more than 0.6 billion years ago. The mitochondria
(and plastids) of extant eukaryotic cells are remarkably similar suggesting
aerobic bacteria (or cyanobacteria) were incorporated on only one occasion
each. We might assume that the evolution of the Eukaryotic cell was a most
unusual event because an amazing array of other cellular characteristics
has evolved over the same period.
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