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Earth is the only planet (and the only body in the universe) we can be certain life exists on, if you count out that accidental tardigrade spill on the Moon. That doesn't necessarily mean we are a cosmic anomaly. If there is life on other planets, there may be a way to find out how it could have evolved before it is ever even found.
Astrobiologist Betül Kaçar realized figuring out how the machinery of life works means that you have to work backwards. She decided to “break” it by using ancestral sequencing to find out how evolution shaped organisms here on Earth — and could shape alien life-forms. She has now found that the process of evolution is surprisingly terrible at multitasking. It just handles the most immediate problem, then moves to the next one without having finished its work on the previous one. Cells don’t resolve issues like we do, which gives us a glimpse at how evolution and natural selection happen on Earth and could occur on other planets.
“In rapidly evolving populations, natural selection may not be able to improve all modules simultaneously because adaptive mutations in different modules compete against each other,” Kaçar said in a study she led, which was recently published in PNAS, adding that “adaptation in some modules would stall, despite the availability of beneficial mutations.”
Cellular modules are molecules that interact to carry out functions within the cell, such as signal transmission and metabolic functions. Translation machinery (TM) is a complex metabolic pathway that creates proteins from information encoded in cells, influencing how living things evolve. It morphs information into proteins that become parts of molecules which can actually do things for the cell and the organism. Kaçar and her team studied what happened when E.coli cells were evolutionarily undone and then had to re-evolve. Enter ancestral sequencing. She genetically engineered the microbes with ancient evolutionary proteins going back as far as 700 million years.
No, this doesn’t mean that resurrecting ancient life-forms Jurassic Park style is actually possible. That would take much more than just a single cell, and much of the dinosaur DNA that has been preserved has broken over the millennia and is too far gone to pull something like that off, though maybe the movie's Mr. DNA (pictured) would disagree.
Translation machinery itself is basically a living fossil. It is thought to have been around for over 3.5 billion years of evolution, but despite that, it obviously never learned how to perfect itself. Kaçar wanted to twist and finally break TM to see how the cells would evolve in response. In the beginning, it seemed that improvements in the warped TM were evidence of natural selection doing what it was expected to do. That didn’t last. Before the cells could fully evolve a solution to restore their broken translational machinery, other cellular modules took precedence. Mutations appeared randomly. Natural selection was supposed to result in the squashing of those mutations, but instead, the process was just as random, though it did lean towards mutations that gave the E.Coli bacteria the best chance at survival.
“Cellular modules may not be fully optimized by natural selection despite the availability of adaptive mutations,” said Kaçar. “If environmental fluctuations are sufficiently frequent…some modules may remain stalled for long periods of time despite being improvable, at least in the absence of recombination.”
Evolutionary stalling has been theorized before, but this is the first time it has ever been proven. The process of evolution can really only handle one thing at a time, and that one thing is the problem that is first to get its attention at the expense of every other issue. Other positive mutations would have seen advancement if the evolutionary process was able to multitask, but those are left behind in what Kaçar and her colleagues call “evolutionary stalling.” The only way to at least somewhat resolve this is the internal exchange of genetic material otherwise known as recombination. This phenomenon happens when that material is transferred between multiple chromosomes or regions of the same chromosome, but she wanted to observe what ended up happening to the E.Coli without it.
Kaçar is not stopping there. For her, the ultimate experiment would be breaking down life to its prebiotic origins and then putting it back together to see how life first formed on Earth and could have possibly emerged elsewhere in the cosmos. Now we can only wait to see what Perseverance unearths on Mars.