We think this is the wrong way round. Ina recent paper, we propose instead that eukaryotic cells evolved from theinside out – that a prokaryote extruded blebs of outermembrane through its cell wall, and these fused to form the peripheral parts ofthe eukaryotic cell that contain the ER and mitochondria (BMC Biology, vol 12, p 76). Likethe famous optical illusion in which one can see either two faces or a candlestick, when theeukaryotic cell is viewed afresh from this perspective, manythings look different. Now the outer membrane of the eukaryotic cell is anevolutionary novelty, while the nuclear envelope corresponds tothe boundary of the original prokaryotic ancestor – the opposite of what isassumed by traditional hypotheses.
Although our inside-out model waspublished last year, the idea was born some 30 years ago when David wasstudying botany at the University of Oxford. Looking at an image of a largeeukaryotic cell next to a much smaller prokaryotic cell, David wondered why itwas always assumed that the boundaries of the two types of cell wereequivalent, when it was easy enough to imagine that the prokaryote cellcorresponded to the nucleus of the eukaryote. His essay on the topic, writtenin 1984, described this basic idea. While it got a respectable mark, it did notseem very compelling at the time. For a start, no prokaryote wasthen known to extrude membrane outwards. David sat on the idea, always thinkingthat somebody else would come forward with the concept, and his research turnedin other directions.
Thirty years later, when David startedto think again about the origin and early evolution of life, he was surprisedto see that, in the interim, nobody had suggested that complexcells arose in this way. Perhaps it required the naiveté of anundergraduate to question dogma? So David dusted off hisinside-out model and wrote up a short piece to explain how it might work andwhy it ought to be considered as an alternative explanation for the origin ofeukaryotes. And it was much more compelling now it is known that theprokaryotes most closely related to eukaryotes, the Archaean,often produce extracellular protrusions. As well as friends andcolleagues, David sent the essay to his cousin, Buzz.
