We have seen that science has discovered the last eukaryotic common ancestor was essentially as complex as a modern day eukaryotic cell (see here and here and here). Furthermore, I have argued that this complex cell plan that has defined eukarya since the time of LECA has worked to facilitate the eventual emergence of metaozoan-type complexity.
So perhaps it is time to begin contemplating the origin of this complexity.
That is, let’s begin to focus on the transition that occurs on the left half of this figure:
So here is the first question to consider. According to the Modern Synthesis, evolutionary transitions occur as small, gradual, incremental steps. Did the complex state of LECA arise through such gradualism? Was it a slow, gradual transition that reached across a huge span of deep time?
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I would guess that a series of incremental improvements in the primordial organellar systems would have accumulated, gradually giving rise to the sophisticated system seen in LECA, but the process that originated the various organelles might have been more saltatory. We do have good
evidence that this is the case for the endosymbiotic organelles. The endomembrane could have been produced by a fusion.
Hi Starbuck,
I’d guess that incremental gradualism was in play when it came to fine-tuning the newly emergent cell type (eukarya). But I don’t think it had much to do with generating the sophisticated complexity exhibited by LECA. I’ll explain my reasoning in the next essay.
It is worth mentioning that endosymbiosis alone clearly means something more was involved than strict gradualism. The origin of eukarya look like a rather special evolutionary transition.
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Hi Mike,
The original enfgulfing would be quick (endosymbiosis) but then the rest could still be gradual- that is the transition to organelles and becoming integrated into the existing system. Unfortunately no one has come up with a way to test the premise that a prokaryote can engulf another in such a way that the engulfed becomes an organelle. So we don’t really know how gradual (or not) the process is.
Also the transition wouldn’t have been from prok to LECA, right?