Explaining Metabolic Innovation: Neo-Darwinism versus Design

Like all life, bacterial life depends on a complex, integrated network of precise metabolic processes. These processes are carried out by more than a thousand enzymes — genetically encoded proteins with information-rich three-dimensional structures that catalyze specific chemical reactions. Can neo-Darwinian theory explain the origin of this network of enzymes that orchestrates metabolic complexity? Building on previous experimental and theoretical work, we argue here that it cannot. But instead of merely listing the theory’s shortcomings, we attempt to construct a full and coherent picture of how it has failed to explain metabolic innovation, from the level of single enzymes all the way up to the network of enzymatic pathways that composes metabolism as a whole. Then, from this critical synthesis we identify six key principles of a new theory of biological innovation. Although these principles only hint at the substance of the new theory, they show clearly that it will be strikingly unlike neo-Darwinism. Whereas the old theory focuses on the simple material processes of mutation and selection in the hope that these can drive innovation, the new one focuses on innovation itself — on the concepts that guide effective designs. Consequently, the new theory will look more like the systematic concepts of an engineering discipline than a set of causal laws.