The origin of the eukaryotic cell.
The endosymbiotic hypothesis for the origin of the eukaryotic cell has been applied to the origin of the mitochondria and chloroplasts.  However as has been pointed out by Mereschowsky in 1905, it should also be applied to the nucleus as well.  If the nucleus, mitochondria and chloroplasts are endosymbionts, then it is likely that the organism that did the engulfing was not a DNA-based organism.  In fact, it is useful to postulate that this organism was a primitive RNA-based organism.  This hypothesis would explain the preponderance of RNA viruses found in eukaryotic cells.  The centriole and basal body do not have a double membrane or DNA.  Like all MTOCs (microtubule organising centres), they have a structural or morphic RNA implicated in their formation.  This would argue for their origin in the early RNA-based organism rather than in an endosymbiotic event involving bacteria.  Finally, the eukaryotic cell uses RNA in ways quite unlike bacteria, thus pointing to a greater emphasis of RNA in both control and structure in the cell.  The origin of the eukaryotic cell may tell us why it rather than its prokaryotic relative evolved into the metazoans who are reading this paper.
Hartman
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Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge 02139, USA.
D005075:Biological Evolution; D002467:Cell Nucleus / Q000502:physiology*; D002875:Chromosomes / Q000502:physiology; D004247:DNA / Q000502:physiology; D005057:Eukaryotic Cells / Q000502:physiology*; D012313:RNA / Q000502:physiology*; D013559:Symbiosis
D012313:RNA; D004247:DNA