Recently, Agnieszka Wołos and colleagues published a study that dramatically complicated the picture of prebiotic chemistry (Science, vol. 369, eaaw1955 [2020]), starting with just six fundamental building blocks—but also demonstrated the synthesis of dozens of known biotic molecules, some by multiple pathways and many in as few as three steps.
The authors used a desktop computer and defined six simple substances thought to be prevalent in prebiotic conditions—methane, ammonia, water, hydrogen cyanide, nitrogen, and hydrogen sulfide—using SMARTS, a coding method used to describe molecules so they can be manipulated by a computer. They then allowed the computer to apply a set of 614 well-known chemical reactions (which they called “transforms”) that change the molecules at a carbon, oxygen, nitrogen, sulfur, or phosphorus atom. These transforms also consider the acidity (from highly acidic to highly basic), the presence of known metallic catalysts (especially copper, zinc, and manganese), the presence of other inorganic reactants (phosphates, acids, and bases), and known reaction yields (from trace to >80 percent yield). They let the computer program run the reactions on the initial starting materials, then took the products of that first iteration (Generation 1 products, or G1) and re-reacted them with the same set of 614 reactions to generate G2, then took the G2 products and reacted them, and so forth. The paper describes their results and directs readers to additional materials available online.
The results are very thought-provoking. Briefly, in the first seven generations, the authors identified 10; 16; 78; 372; 1,115; 9,163; and 34,284 compounds having masses of less than 300 (a self-imposed size limit to keep the data manageable). Of these, eighty-two are biotic molecules: amino acids, peptides, nucleic acid bases, carbohydrates, and other known metabolites such as lactic acid. The authors set up an online gateway (which can be accessed at www.allchemy.net; new accounts are free) that can be used to explore the details of their work as well as continue developing generations.
The paper is not just an announcement of molecules being synthesized. The researchers noted that while most of the reaction pathways are already found in previous literature, they discovered that their network of chemical reactions gave several new pathways to synthesize biotic molecules. One example they gave was uric acid, which is a product of the chemical breakdown of certain DNA nucleotides and is excreted in urine. Although uric acid has been identified as a product in some previous origin-of-life research, it was detected only in trace amounts, while the new pathway (which the authors verified experimentally by carrying out the reactions in the computer-generated pathway) produced uric acid in five synthetic steps and had an overall yield of 1 percent.
The authors made three additional points that have particular meaning to the origin-of-life research community. First, the network generated some compounds that were able to catalyze reactions in higher generations. For example, they noted the formation of formaldehyde in G2, which can act as a catalyst in certain hydrolysis reactions and dramatically increase their yields. Analysis of the network indicated that the presence of formaldehyde led directly to the formation of 2,600 new molecules that would otherwise not be synthesized. Acetate, imidazole, phenylalanine (an essential amino acid), and iminodiacetic acid (IDA) were also noted catalysts, ultimately contributing to the formation of over 21,500 new molecules.
Second was the appearance of chemical cycles, in which products of later generations could serve as feedstock for previous generations and become self-generating with the input of additional reactants—just like a living organism does. Again, the authors experimentally verified one of the cycles involving IDA and noted a yield of 126 percent, indicating a regeneration of more IDA in the cycle than was originally reacted.
Third, and most potentially interesting, was the detection of molecules known as surfactants, a type of chemical that acts as a “surface active agent.” In this study, surfactant molecules such as fatty acids were predicted to form. In real life, surfactants are long-chain molecules that typically have an electrical charge on one end, although there are some neutral (not electrically charged) surfactants. Surfactants are used as soaps and detergents and occasionally as antimicrobial agents. In living organisms, surfactant molecules are used to make what the authors call “biological compartmentalization[s]”—that is, cells. A careful reading of the paper suggests that the formation of fatty acid surfactants may be a prediction unique to this network, although surfactants comprising short chains of certain amino acids were found in previous studies.
What does all this mean? First, it does not mean that we know how life arose from a prebiotic Earth. However, this is another piece of the puzzle that suggests that there is little barrier for the chemicals of non-life to become the chemicals of life. After all, the theory of vitalism—that the chemicals of living organisms are fundamentally different from the chemicals of non-life—was disproven about 200 years ago. Nor has it ever been demonstrated that it is not possible to transform non-living chemicals into chemicals of life. If that were ever demonstrated, creationists would have one real scientific argument in their arsenal instead of just vapid rhetoric. Nope, sorry—this work is another demonstration that not only are the chemicals of life rather easy to synthesize, but they may also be inevitable.