Scientists have been working for generations to untangle the mysteries of how life on Earth began, and a previously fringe theory has just gained a lot of traction.
The ‘RNA World’ theory says that the so-called primordial soup of early Earth was teeming with DNA’s single-stranded sister RNA, which carries the instructions for sustaining life.
Now a team of researchers at the Salk Institute has unlocked a crucial piece of that puzzle and even built it in the lab: an obscure but essential class of molecules called RNA polymerase ribozymes.
RNA polymerase ribozymes are not yet well understood, but scientists now suspect that these substances made it possible for RNA to not only multiply, but even evolve in the gel and mud of the early planet.
These scatterplots show how, over multiple rounds of evolution, new RNA polymerase ribozymes emerged. A lower quality version (top) drifted from their original sequence and tended towards randomness, while a higher quality version (bottom) retained their original function and developed new sequences.
Although little is known about RNA polymerase ribozymes, scientists know that they can copy RNA strands.
In laboratory experiments, scientists have shown that this is not all they can do.
Apparently they can evolve too.
Their experiments showed that RNA polymerase ribozymes can not only copy RNA, but they can also become better at it.
Over time, they noticed that the RNA polymerase ribozymes that constructed copies of themselves could also copy RNA.
And the copies were not only functional, but even became better at copying RNA – the same kind of evolution described by Charles Darwin.
As Darwin described evolution, the ‘fitter’ an organism is, the more likely it is to reproduce and pass on its genetic material.
He didn’t know anything about DNA, but DNA is how genes are passed on.
The new experiment suggests that some kind of evolution may have occurred in the RNA World scenario.
As certain RNA polymerase ribozymes became better at copying RNA, they became more likely to stick around and continue to serve their roles.
In contrast, those of lower quality copied the RNA less reliably and their sequences drifted away and became more random across multiple evolutionary trajectories.
There may not even have been DNA to pass on, but evolution was happening, the authors of the new study said.
“We are chasing the beginnings of evolution,” senior study author and Salk president Gerald Joyce said in a statement.
“By unveiling these new capabilities of RNA, we discover the potential origins of life itself, and how simple molecules could have paved the way for the complexity and diversity of life we see today.”
The study was published in the magazine Proceedings of the National Academy of Sciences.
Eventually, RNA came together to form the better-known double-stranded structure of DNA, creating single-celled organisms and then more complex life forms.
These are all just theories, as we can never go back to the beginning of the planet and confirm how it all started.
But building RNA polymerase ribozymes in the lab and seeing how they help RNA evolve adds weight to the RNA World theory because it shows that this was theoretically possible.
The early Earth may have contained the ingredients for life long before anything lived on our planet. Scientists now have evidence that these materials may even have evolved on their own
RNA is like the single-stranded version of DNA and contains the pieces of genetic material that cells use to communicate.
Proteins, the basic materials of living things, are constructed using the instructions in RNA.
He is an unsung hero of life. It always works, and without it we would die, but DNA usually gets the credit.
“We have long wondered how simple life was in the beginning and when it gained the ability to improve itself,” said first study author Nikolaos Papastavrou, a research associate in Joyce’s lab.
‘This study suggests that the beginnings of evolution could have been very early and very simple. Something at the level of individual molecules could have sustained Darwinian evolution, and that could have been the spark that caused life to become more complex, from molecules to cells to multicellular organisms.’
Some scientists claim that life on asteroids was delivered from the stars, while others say the building blocks for life came from space and were assembled into life forms on Earth. An older idea holds that the basic molecules of life assembled themselves here on Earth from non-organic compounds.
Without RNA, most of the body’s functions would not be possible. RNA contains instructions for building proteins, which underlie almost everything cells do.
Long before animals and single-celled organisms existed, the early Earth may have been home to strands of genetic material – and more importantly, the chemicals that make them replicate.
The work of Joyce and Papastavrou’s team will need to be replicated by other researchers, but for now it represents a sign in favor of one theory of how life originated.
The team said they hope they can even discover how new RNA functions are invented through the same evolutionary process.