Measuring heritability in messy prebiotic chemical systems

Abstract

A key question in origins-of-life research, is whether heritability, and thus evolution, could have preceded genes. While theoretical research has shown that out of equilibrium chemical reaction networks with multiple autocatalytic motifs can provide chemical “memory” and serve as units of heritability, experimental validation is lacking. We established conditions that may be conducive to these processes and developed methods to seek evidence of heritability. We prepared a food set (FS) of three small organic species (methanol, formic acid, and acetic acid), three inorganic salts (sodium trimetaphosphate, ammonium hydroxide, sodium bicarbonate), and pyrite mineral. We conducted a serial dilution experiment where FS was assembled, autoclaved, and the incubated for 24 hours, after which a 20% fraction was transferred into freshly prepared FS that went through the same procedure. This process was repeated for 10 transfer (TR) generations. To serve as controls, we also incubated the fresh solutions in each generation. Over the course of the experiment, we compared the chemical composition of transfer (TR) vials and no-transfer control (NTC) vials using liquid chromatography-mass spectrometry (LCMS). We adapted metrics from ecology and evolutionary biology to analyze the chemical composition data, finding a great deal of variability. Nonetheless, by focusing on a subset of the chemicals with more consistent patterns, we found evidence of heritable variation among vials.