A form of natural selection could have modified the amino acids in the “primordial soup” long before life appeared on Earth.
Although the basic mechanisms have been discovered, the details of exactly how life emerged from inanimate matter remain a mystery. A A new study finds that natural selection may have played a role in this process.even before life itself existed on Earth.
in the famous Miller and Urey experimentby recreating the “primal soup”, a mixture of elements present in the Earth’s origins, the scientists discovered that a cocktail of amino acids, the molecules that make up proteins and that compose the genetic code of all forms of life on the planet, spontaneously formed.
Although there are hundreds of different amino acids in nature, all living organisms, from bacteria to elephants, contain a basic set of 20 amino acids. That’s because everything can be traced back through a complex tree of life to a single microscopic common ancestor that existed billions of years ago. But what’s so special about these 20 amino acids? This was the goal of scientists at Johns Hopkins University and Charles University.
The team recreated the conditions of early Earth in the laboratory, including a mix of amino acids that were very common before the emergence of life. Some of them are believed to have been produced when ultraviolet light from the Sun interacted with gases in the atmosphere at the time, while others came aboard meteorites that hit the planet more often than now.
In their experiments, the researchers observed that a kind of natural selection process took place, even in the absence of life. Ancient organic compounds tended to integrate into their biochemistry the amino acids best suited to folding proteins into key forms for vital functions, giving these compounds a better chance of survival. Given enough time, there were simply more organic compounds with life-friendly properties.
This means that protein folding allowed evolution before there was even life on our planet. Before there was DNA, there was natural selection of chemicals useful for life..
Scientists say this process could help explain the mysterious transition between non-living matter and living organisms. Once the first extremely simple forms of life were created, they could evolve into everything that has existed in the billions of years since then, retaining those “special” amino acids.
For there to be evolution in the Darwinian sense, a sophisticated system for transforming genetic molecules such as DNA and RNA into proteins is necessary. But to replicate DNA, you also need protein, so we have a chicken-and-egg problem. This research shows that nature could have selected building blocks with useful properties before Darwinian evolution.
This study doesn’t just have implications for life on Earth: similar rules could also apply on other worlds. For example, amino acids have been detected in comets and asteroids and seem to be quite common around. According to one of the lead authors, Stephen Fried, “It seems the universe loves amino acids, maybe if we found life on another planet it wouldn’t be so different.”
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Early selection of the amino acid alphabet was adaptively shaped by biophysical folding constraints
Photograph: NASA Goddard Space Flight Center
