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Quotes on the endosymbiotic theory

In this post I collect statements about the evolution of mitochondria that claim that the endosymbiotic theory is a fact. I hope that after reading my alternative theory you may look at the statements below in a different light. By the way, if it would be a fact, you wouldn’t need to stress that all the time. I don’t see physics articles starting by claiming that gravity is proven beyong reasonable doubt, or in geology that the earth is round. You can judge from my site if the bold statements below are in fact backed up with evidence and mechanisms.

  • “Biochemical and molecular data attest beyond all reasonable doubt to the view that plastids descend from cyanobacteria and that mitochondria descend from -proteobacteria”, Martin, 1999
  • It is now apparent that eukaryotic microbes that lack typical mitochondria are not primitively amitochondrial but are highly derived descendants of mitochondrion containing ancestors whose capacity for aerobic respiration has been gradually lost during the course of evolution”, Leon-Avila and Tovar, 2004.
  • “The Archezoa hypothesis, now abandoned by its original proposer (Cavalier-Smith, 2002), crumbled under the weight of evidence for the presence of relict mitochondrial organelles in several organisms representative of the major amitochondrial eukaryotic lineages (Archeoamiba, Metamonada, Parabasalia and Microsporidia), rejecting the idea that those organisms diverged from the main eukaryotic trunk prior to the endosymbiotic acquisition of the mitochondrion”, Leon-Avila and Tovar, 2004.
  • “The evolutionary origin of the mitochondria from an endosymbiotic bacterial cell is now a historical fact and no longer a hypothesis. This must be concluded after the analysis of some 900 mitochondrial and several hundred complete bacterial genomes.” On website Laboratory for Evolutionary Biology, Center for Mitochondrial Diseases.
  • Biologists agree that the ancestor of mitochondria was an alpha-proteobacterium.”  Esser, Martin and Dagan 2006.
  • “A new report has uncovered DNA in the hydrogenosomes of anaerobic ciliates. The sequences show that these hydrogenosomes are, without a doubt, mitochondria in the evolutionary sense, even though they differ from typical mitochondria in various biochemical properties.” Martin, 2006.
  • “The old view […] held back progress in the field like a yoke. It is a real relief that we can now look forward. David Lloyd, Martin Embley and Jorge Tovar here.
  • “This bug is an impostor, posing as a primitive cell when in reality it is a highly evolved organism with mitochondrion-bearing ancestors,” explains Dr Tovar. “Giardia has done a sterling job of concealing all evidence of its mitochondrial ancestry. Little wonder that over the past 100 years or so most biologists were fooled into thinking of it as a primitive microbe.” Jorge Tovar here.
  • “Of course, there will be folks who will even doubt the evidence presented by Tovar and his colleagues, and there will be folks who dream up hair-brained scenarios to suggest that the Giardia organelles descend from something else other than mitochondria. Let them dream on.” Bill Martin here.
  • The hypothesis of bacterial origin of mitochondria, […] can now be considered as a factually substantiated theory. Kuznetsov and Lebkova, 2002)
  • “Thus, the analysis of the Rickettsia prowazekii genome lends further, virtually incontrovertible, support to the notion of the common ancestry of mitochondria and contemporary a-proteobacteria.” Mueller and Martin, 1999.
  • Mitochondria originated by permanent enslavement of purple non-sulphur bacteria“. Thomas Cavalier-Smith, here.
  • “Giardia’s place as intermediate stage in standard schemes of eukaryotic evolutionary history is no longer tenable. They don’t want it [Giardia] to have mitochondria because it spoils their soup… This thinking is deeply ingrained”. Bill Martin, from here.
  • “Mitochondria are generally accepted to have descended from a eubacterium that was engulfed by an archaebacterial host cell” (Lister and Whelan, 2006).
  • “Mitochondria evolved from free-living alpha-proteobacteria following a single endosymbiotic event over one billion years ago” (Logan, 2006).
  • “By now, with many mitochondrial genomes fully sequenced, and with complete sequences also available fo such crucial bacteria as Rickettsia (Andersson et al., 1998) and other a-proteobacteria, it is undisputable that the mitochondrion and its genome are of endosymbiotic origin, i.e., that they are the derived remnants of a once free living bacterium, almost certainly an a-proteobacterium” (Adams and Palmer, 2003).
  • “ATP production, coupled to electron transport, and translation of mitochondrial proteins represent the essence of mitochondrial function: these functions are common to all mitochondrial genomes and can be traced unambiguously and directly to an α-proteobacterial ancestor” (Gray et al., 2001).
  • This has not happened with the debate on how eukaryotes (animals, plants, fungi, protists) arose. The conflicting hypotheses currently on offer show a curious disregard for mechanism. One thing at least is agreed: the mitochondrion, powerhouse of the eukaryote cell, evolved from an engulfed bacterium. The question is ‘who’ did the engulfing (Poole and Penny, 2007).
  • One of the major advancements in understanding eukaryotic evolution was the discovery that mitochondria evolved from an endosymbiotic α-Proteobacterium, and that mitochondrial DNA (mtDNA) is a relict bacterial genome. Most mtDNAs have lost earmarks of their bacterial origin, with a notable exception in jakobid flagellates (Lang et al., 2005)
  • Mitochondria are now known to have arisen by endosymbiosis involving an alpha-proteobacterium.The most compelling evidence for this comes from similarities between gene sequences from alphaproteobacterial genomes and their homologues in the relic genomes of the mitochondria (Slamovits and Keeling, 2007).