The Evolution of Myelin: Theories and Application to Human Disease

Abstract

Myelin, once thought of as a simple insulating sheath, is now known to be a complex, dynamic structure. It has multiple functions in addition to increasing conduction velocity, including reducing the energetic cost of action potentials, saving space, and metabolic functions. Myelin is also notable for likely having arisen independently at least three times over the course of evolutionary history. This article reviews the available evidence about the evolution of myelin and proposes a hypothesis of how it arose in vertebrates. It then discusses the evolutionary trade-offs associated with myelination and suggests a possible animal model for further study of this phenomenon. Finally, it briefly covers the neural regulation of myelination before discussing possible roles of myelin in human social cognition and evolution, and the relevance of this to human disease.