Andreas Wagner (University of Zürich; SFI External Professor)
Abstract. Some evolutionary innovations may originate non-adaptively as exaptations, or pre-adaptations, which are by-products of other adaptive traits. Examples include feathers, which originated before they were used in flight, and lens crystallins, which are light-refracting proteins that originated as enzymes. The question of how often adaptive traits have non-adaptive origins has profound implications for evolutionary biology, but is difficult to address systematically. Here I consider this issue in metabolism, one of the most ancient biological systems that is central to all life, and discuss recent observations suggesting that any one adaptation in a complex metabolic reaction network entails multiple potential exaptations. Metabolic systems thus contain a latent potential for evolutionary innovations with non-adaptive origins. These observations suggest that many more metabolic traits may have non-adaptive origins than is appreciated at present. More generally, they challenge our ability to distinguish adaptive from non-adaptive traits.