Scientists think that mitochondria were once independent single-celled organisms until, more than a billion years ago, they were swallowed by larger cells. Instead of being digested, they settled down and developed a mutually beneficial relationship developed with their hosts that eventually enabled the rise of more complex life, like today’s plants and animals.
Most of their DNA is outsourced to the cell’s nucleus, but why not all of it? In humans, all but 37 are outsourced. In a large project involving more than 2000 mitochondrial genomes from a variety of life forms, researchers found
All of the mitochondria’s remaining genes help produce energy in some way. But the team found that a gene was more likely to stick around if it created a protein that was central to one of these complexes. …
“Keeping those genes locally in the mitochondria gives the cell a way to individually control mitochondria,” Johnston says, because pivotal proteins are created in the mitochondria themselves. That local control means the cell can more quickly and efficiently regulate energy production moment-to-moment in individual mitochondria, instead of having to make sweeping changes to the hundreds or thousands of mitochondria it contains. For instance, out-of-whack mitochondrion can be fixed individually rather than triggering a blanket, cell-wide response that might then throw something else off balance.
It’s like responding to a fire, says John Allen, a biologist at University College London who was not involved in the study. If a single room in a large building goes up in flames, you don’t phone the building manager to ask permission to put it out. You grab a fire extinguisher and aim More.
That’s a lot of decision-making for natural selection acting on random mutations to do. And the way these researchers talk, it sounds like a design inference.
So is this how it will be? We finally find the explanations and contrary to decades-long explanation, they cannot possibly be Darwinian. And no one even talks as though they are.
Now, if someone shoved a mike or a fist in that guy’s face, he might think up some Darwinism to get out the mess. Indeed, he might feel it his duty, might even believe it himself. But for many, sooner or later, a sense of the ridiculous surely sets in.
See also: Cells were complex even before mitochondria? Researchers: Our work demonstrates that the acquisition of mitochondria occurred late in cell evolution, host cell already had a certain degree of complexity
Sean Pitman on the evolution of mitochondria
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Here’s the summary:
Since their endosymbiotic origin, mitochondria have lost most of their genes. Although many selective mechanisms underlying the evolution of mitochondrial genomes have been proposed, a data-driven exploration of these hypotheses is lacking, and a quantitatively supported consensus remains absent. We developed HyperTraPS, a methodology coupling stochastic modeling with Bayesian inference, to identify the ordering of evolutionary events and suggest their causes. Using 2015 complete mitochondrial genomes, we inferred evolutionary trajectories of mtDNA gene loss across the eukaryotic tree of life. We find that proteins comprising the structural cores of the electron transport chain are preferentially encoded within mitochondrial genomes across eukaryotes. A combination of high GC content and high protein hydrophobicity is required to explain patterns of mtDNA gene retention; a model that accounts for these selective pressures can also predict the success of artificial gene transfer experiments in vivo. This work provides a general method for data-driven inference of the ordering of evolutionary and progressive events, here identifying the distinct features shaping mitochondrial genomes of present-day species. (Public access) – Iain G. Johnston, Ben P. Williams Evolutionary Inference across Eukaryotes Identifies Specific Pressures Favoring Mitochondrial Gene Retention Cell Systems Volume 2, Issue 2, p101–111, 24 February 2016