An Ecology-First Approach to the Origins of Chemical Evolution

What is an adaptive chemical system and how could one arise? One distinguishing characteristic that has largely been ignored is molecular complementarity, which is ubiquitous in living systems but rare elsewhere in nature.  Molecular complementarity makes possible the evolution of chemical systems in several ways. It 1) provides a natural means of selecting, stabilizing, and producing homeostatic modules; 2) as Herb Simon has demonstrated, such stable, complementary modules can form hierarchically organized systems far more efficiently than can probabilistic mechanisms; 3) molecular complementarity captures information through organization; 4) and the resulting aggregates can, as Doron Lancet has proposed, use compositional replication as a form of chemical “inheritance”. As a consequence of these four points, several principles characterize living chemical systems.  One is that the emergence of adaptive systems is a function of chemical interactions that select for survival of the fittest sets of compounds. In other words, evolution proceeds by evolving chemical ecologies, not by selecting for individual molecules. A second principle is that as a result of selection for ecological sets of complementary sets of compounds, there is a molecular paleontology embedded within modern biological systems manifested through modules involving small, molecularly complementary subunits. These modular subunits are the bases of modern macromolecular structures such as receptors and transporters. For example, Donard Dwyer has proposed that self-aggregating peptides became the bases of their own receptors, and indeed, insulin, which self-aggregates, has multiple insulin-like regions forming its receptor binding sites. A third principle is that these molecularly complementary modules are conserved and repurposed throughout evolution. Glucose binds to insulin and insulin-like modules also form the transport core of glucose transporters. A fourth principle is that molecules that bind to each other alter each other’s physiological effects; and conversely, molecules that have antagonistic or synergistic physiological effects bind to each other. Glucagon, which antagonizes insulin activity, not only binds to insulin, but co-crystallizes with it. This binding-mediates-function principle suggests that biological structure and function evolved from a physicochemical basis in which molecules chemically select each other for their functions. Present-day molecular systems can therefore reveal the physicochemical criteria by which they evolved from the simplest chemical origins.