Supply-driven evolution: mutation bias and trait-fitness distributions can drive macro-evolutionary dynamics

Abstract

Many well-documented macro-evolutionary phenomena, such as increases in organization hierarchy, or sudden and episodic creation of new taxa, still challenge current evolutionary theories. Here we show a new mechanism that can explain them. We begin by showing how the order of mutations can alter evolutionary trajectories. We present a framework integrating both mutation and environmental biases and show that mutation bias can strongly outweigh any environmental bias, a regime we call "supply-driven" evolution. We then show how a common type of mutation bias, where detrimental mutations are more common than beneficial mutations, can drive the locking-in of structural hierarchies such as eukaryotism or multicellularity, independently from the environment. Finally, we generalize this result to show how any mutation (or sets of mutations) that creates the possibility of new phenotypes can persist for a very long period of time. That is, innovations that make possible a large range of new phenotypes can become frozen in time. By becoming frozen, these novel structures can no longer change, which means a range of phenotypes also become impossible. This opening and closing of phenotypic space is a new mechanism of macro-evolution.