Are the backbones of life the result of Darwinian evolution or something more ancient?
In short: Our bodies function like self-regulating factories, relying on biological polymers like proteins and DNA to survive. While we know how these molecules evolve, the origins of their fundamental backbones remain a mystery. New research suggests these structures may have emerged through a pre-Darwinian process of chemical coevolution.
Biological polymers—specifically polypeptides, polynucleotides, and polyglycans—are essential to life, yet they present a scientific paradox. These backbones are thermodynamically unstable and kinetically trapped in aqueous environments, meaning they should naturally break down. Despite this, they persist, forming complex, mutualistic networks within cells that function like an Amazon Jungle of molecules. Because Darwinian evolution relies on these pre-existing backbones to function, it cannot explain how they were originally formed.
Researchers propose that these molecules emerged during the Hadean Earth period through non-Darwinian coevolution. Driven by environmental stressors like hydrolytic pressure, these chemical species underwent iterative cycles of sculpting and selection. This model suggests that biopolymer backbones are not mere remnants of prebiotic chemistry, as conventional theories often claim. Instead, they are the result of a seamless transition from chemical evolution to the Darwinian processes we recognize today, potentially explaining why ribosomes, composed of RNA and protein, remain consistent across the entire tree of life.
A key mechanism in this emergence is 'polyfunction' and 'function-switching,' where subtle chemical changes—such as altering a linkage site or the reduction of ribose—drastically change a molecule's structure and utility. Furthermore, assembly plays a critical role in survival; when these polymers assemble, they modulate their own thermodynamics, protecting themselves from hydrolysis. This 'recalcitrance' suggests that the ability to form stable assemblies was a primary selective force during the early chemical evolution of life, allowing these building blocks to persist long enough to become the foundation of modern biology.
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Sources
- Summary by Intellect · source: Biological Polymers: Crash Course Organic Chemistry #49
- Also: Biological Polymers: Evolution, Function, and Significance
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