A Chimeric Paradigm

In 1998, William Martin and Miklos Muller challenged the two core features of the standard archezoan symbiotic scenario  

They denied the existence of the Archezoa as a phylogenetic taxon because there was no evidence of protists today that did not once possess mitochondria (Martin and Muller 1998 see also Martin et al. 2001). 

They rejected the oxygen context for the selective advantage of the protomitochondrial symbionts to their host based on increased efficiency in ATP production through respiratory carbohydrate breakdown. 

As they saw it, that scenario was not only purely speculative, but was based on erroneous assumptions. There was no evidence now or then of a bacterium of any kind that did not produce sufficient amounts of ATP, like the host in that narrative. Nor was there any evidence of a bacterium, like the original theorized symbiont, that produced more ATP than it needed to provide to its host. They proposed instead that the nucleated protist evolved after the acquisition of protomitochondria by an archaebacterial host in an anaerobic context. 

Were bacteria incapable of acquiring symbionts The assumption that only eukaryotes possessed a cytoskeleton and were therefore capable of phagocytosis had been a chief reason for postulating the archezoan host in the first place. As Cavalier-Smith (1987b, p. 56) put it forcefully, it is only the existence of such fully eukaryotic phagotrophs that makes a symbiotic origin of mitochondria mechanistically plausible no bacteria, not even predatory ones, can take up or harbor other living cells in their cytoplasm, and to 

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