How Well Do Evolutionists Understand Endosymbiosis?
The theory that early cells engulfed microbes that became mitochondria is often presented overconfidently.
Most evolutionists accept without question the decades-old theory that mitochondria and chloroplasts are the remnants of free-living organisms that took to living inside a host. For instance, a paper in Current Biology (2012) states, “It is beyond doubt that mitochondria and plastids (chloroplasts) evolved from free-living organisms enslaved by other cells.” Whether through parasitism or predation, these microbes became accepted as endosymbionts (partners living inside) of other microbes; that’s part of the common story of the origin of eukaryotes. The endosymbionts changed over evolutionary time, sending some of their genomes into the nucleus but retaining some of their own DNA inside the organelles they were destined to become.
How solid is this theory? An article in Science (Ball, Battacharya and Weber, “Pathogen to Powerhouse”) makes it look less confident than often presented. Some excerpts:
- Primary endosymbiosis is extremely rare: Only one other case is known, in the amoeba Paulinella. This rarity is usually attributed to the many innovations that are required for organelles to be integrated into the cellular machinery.
- However, the first challenges for an endosymbiont are to avoid being digested by the host and to replicate in its novel environment.
- These results [i.e., a lone case of an endosymbiont surviving its host’s defenses] also help explain why ancestrally mitochondrion-lacking eukaryotes (so-called archezoans) have never been found: They likely do not exist.
- When we turn our attention to primary plastid origin, the story becomes more complex.
- Living cyanobacteria neither possess the genetic toolkit to evade host defenses, nor do they encode effector proteins to interact with the host cellular machinery. So, how did the unprotected photosynthetic cell survive the early phases of the endosymbiosis? A potential solution to this conundrum was provided by the discovery of several dozen genes of chlamydial origin in the nuclear genome of algae and plants…. However, the details of this complex process remain incompletely understood.
- As the recent studies discussed here show, we are in an exciting phase of endosymbiosis research. However, we still lack some crucial information.
- The Lokiarchaeota [the presumed ancient hosts] were identified from assembly of metagenomic data; no living cells have yet been isolated to validate the genome assembly or test their actual physiological capabilities.
- Protist-infecting chlamydial cells with large genomes are continuously being isolated, but only a handful have been studied in detail and are represented in genome databases. Therefore, more data are needed to test the proposed role of pathogens in organelle origin.
- But perhaps what we need most are attempts at experimental primary endosymbiosis in the lab to learn the rules underlying this remarkable process.
- Ultimately, these advances will help us address the most vexing question about primary endosymbiosis: Why is it so rare?
In short, endosymbiosis is a convenient anecdote, but it has not been tested, and it may not be testable. It’s never been seen occurring in nature except for the one putative case they mentioned. It has never been reproduced in the lab. In the philosophy of science, one-time ad hoc events needed to explain a phenomenon are frowned upon because they open a theory to accusations of special pleading.
It is not necessary for creationists to repudiate all instances of endosymbiosis. Parasitism is very prevalent in nature, as is mutualistic symbiosis. But to say that this was a “great transformation” in the history of evolutionary common descent that “gave rise” to all eukaryotes (including humans) by an accidental process— that is a story, not a testable theory. It goes way, way overboard. Even if scientists observe an endosymbiotic event in nature or in the lab, it will not prove that’s what happened in the distant unobservable past.
Even less testable is the idea that rare endosymbiotic events gave rise to whole lineages of future innovations. The only reason evolutionists are so tempted by the endosymbiosis theory is that they have a huge hurdle to leap over with Darwin faith. There are three main kingdoms of life (if one accepts the current consensus taxonomy), the archaea, the bacteria, and the eukarya. Eukaryotes are the only ones with organelles and a nucleus. It’s tempting for Darwinists to see a sequence there: a bacterium engulfed an archeon, and presto! A eukaryote was born. Michael Denton points out in his new book Evolution: Still a Theory in Crisis that even if this were true, it would not have been a gradual, Darwinian process. It would have been a saltational event, a dramatic leap in innovation. And bacteria, remember, have those amazing outboard motors (flagella). No living cell is primitive!
Creationists have reasons to believe that microbes were created essentially as they are, except for degradation and parasitism that occurred after the Fall. Mitochondria and chloroplasts are too marvelously engineered for their functions as to have had an accidental origin. Observations about partial genomes in the organelles and other parts in the nucleus may be puzzling, but remember Nelson’s Principle: “If something works, it didn’t happen by accident” (quote in Flight: The Genius of Birds). There may be good reasons for the split genomes. The transporters that carry products of nuclear translation into the organelles are also amazingly complex and effective.
Evolutionists have massive puzzles to explain. The ATP synthase motors in mitochondria and the photosystems in plastids are complex almost beyond description; where did they come from? How did the ancestors invent those? The endosymbiont theory doesn’t explain that, nor does it explain any of the subsequent “Great Transformations” natural selection would have to perform with Darwin Flubber to get from the first eukaryote to a kangaroo, a titanosaur or a human brain. Endosymbiosis is just a cute story that makes evolutionists feel good, as if they have made some progress in articulating the Grand Myth.*
*Weinberg’s Principle: “an expert is a person who ignores the small errors while sweeping on to the grand fallacy.”