On the dynamics of prebiotic evolution

The question of how life arose from non-living matter is the focal mystery where chemistry and molecular biology converge with evolutionary biology. But although it exemplifies the scientific challenge of explaining how and why complex phenomena appear in nature, it defies standard methods of scientific inquiry. The first life to assemble abiotically left no fossils, and scientists are unlikely to prove anything definite about its identity. Instead, origins of life researchers look for conditions under which non-living material assumes certain properties of living material, trying to bridge the chasmal gap that separates living and nonliving chemistry today. In 1828, Friedrich Wohler’s urea synthesis proved that organic molecules can be obtained from inorganic ones via ordinary chemical reactions [36], debunking the 17th century belief that organic materials owe their heat-sensitivity to a “vital energy” that is absent from inorganic material [37]. Wohler’s work ignited a science of organic chemistry that has used simple physics to explain most unique properties of biomolecules; in particular, chemists have found many chemical conditions that promote predictable interconversions between organic and inorganic matter. In 1959, Stanley Miller proved that such conditions need not be highly artificial, synthesizing DNA and protein building blocks within an apparatus that simulated a lightening storm over a pool of common sludge [27]. James Ferris later proved that charged clay surfaces and drying conditions are enough to promote the polymerization of complex RNA chains [13]. Such work has effectively demystified the chemical split between life and non-life; although we will never know with certainty how the chemical components of life first appeared on Earth, their presence can be explained in many plausible ways. However, there are no equally satisfying explanations for the advent of self-replication and metabolism, behaviors that biochemicals only exhibit when organized into complex systems. By creating a scientific landscape where the difference between synthetic organic material and natural organic material is organizational complexity, 19th and 20th century biochemists have turned the origins of life question from a chemical synthesis problem into an information-theoretic problem. The supposed manifestation of 17th century “vital force” in heat sensitivity was spot on in that a protein fails to reconstitute after heating because the information content of its three-dimensional fold has been destroyed. When a protein cannot assume its bio-active, water-soluble native configuration without help from the cellular machinery that its own catalytic activity helps maintain, we are faced with the sort of chicken-or-egg dilemma that creates so much of the mystique surrounding the origins of biological systems. But just as paleontologists know that eggs preceded chickens by millions of years, modern biochemists know that there exist certain proteins that are capable of reconstituting after being heated because they assume their native folds spontaneously. Furthermore, it is well understood via the theory of energy landscapes why certain proteins fold spontaneously and others do not [20]. The information contained in a spontaneously folding protein sequence can propagate itself if it encodes a structure that catalyzes its own replication, as was demonstrated by the