Exactly how life arose out of non-living matter is a major mystery, and a new study has found that natural selection may have played a role before life itself even existed on Earth. By recreating the primordial soup, scientists identified how a cocktail of specific amino acids informed the genetic code of every single lifeform on the planet.
Although there are hundreds of different amino acids in nature, a core set of 20 can be found in every living organism, from E. coli to elephants. That’s because everything can be traced back through a complex tree of life to a single common ancestor that existed billions of years ago. But what’s so special about these 20 specific amino acids? Finding out was the goal of a new study co-led by scientists from Johns Hopkins University and Charles University.
The team recreated the conditions of early Earth in the lab, including a mix of amino acids that were very common before life ever appeared. Some of these are believed to have been produced when UV light from the Sun interacted with gases in the atmosphere of the time, while others arrived aboard meteorites that impacted the planet more often than they do now.
In their experiments, the team observed a kind of natural selection process taking place, even in the absence of life. Ancient organic compounds tended to integrate into their biochemistry the amino acids that were best suited for folding proteins into shapes key to vital functions, which gave these compounds a better chance at surviving. Give it enough time and there were simply more organic compounds with properties favorable to life.
“Protein folding was basically allowing us to do evolution before there was even life on our planet,” said Stephen Fried, co-lead author of the study. “You could have evolution before you had biology, you could have natural selection for the chemicals that are useful for life even before there was DNA.”
The team says that this process could help explain the mysterious transition between non-living matter and living organisms. Once the first extremely simple lifeforms had been sparked, they could then go on to evolve into everything else that’s ever lived in the billions of years since, conserving those “special” amino acids.
“To have evolution in the Darwinian sense, you need to have this whole sophisticated way of turning genetic molecules like DNA and RNA into proteins,” said Fried. “But replicating DNA also requires proteins, so we have a chicken-and-egg problem. Our research shows that nature could have selected for building blocks with useful properties before Darwinian evolution.”
This study doesn’t just have implications for life on Earth – similar rules could apply on other worlds too. After all, amino acids have been detected in comets and asteroids, and seem to be fairly common out there.
“The universe seems to love amino acids,” said Fried. “Maybe if we found life on a different planet, it wouldn't be that different.”
The research was published in the Journal of the American Chemical Society.
Source: Johns Hopkins University
