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Cells from eukaryotic organisms (e.g. Animals, Plants, Fungi, Protists) differ from those of the prokaryotes (Bacteria and Archaea) in a large number of characteristics. These differences are so vast that the evolution of the eukaryotic cell from prokaryotic ancestors is widely regarded as a major evolutionary discontinuity.[1,2] Although there are no clear intermediates in this transition, the available evidence strongly indicates that eukaryotic cells have evolved much later (only about 1-1.5 billion years ago) in comparison to the prokaryotic organisms, which existed as far back as 3.5-3.8 Ga ago.[3] The question thus arises how did the transition from prokaryotic to eukaryotic cell come about and who are the progenitors of the ancestral eukaryotic cell?[4]

http://bacterialphylogeny.com/eukaryotes.html

[Reeses]

who are the progenitors of the ancestral eukaryotic cell?

One theory is that two very different prokaryotic life forms merged into one complex cell. Possibly a parasitic organism lived inside another until their systems evolved to become dependent and indistinguishable. A complex life form might be a multimillion year collection of thousands of other life forms of widely different talents that became functionally one.

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