A developmental perspective on the evolution of the nervous system

The evolution of nervous systems in animals has always fascinated biologists, and thus multiple evolutionary scenarios have been proposed to explain the appearance of neurons and complex neuronal centers. However, the absence of a robust phylogenetic framework for animal interrelationships, the lack of a mechanistic understanding of development, and a recapitulative view of animal ontogeny have traditionally limited these scenarios. Only recently, the integration of advanced molecular and morphological studies in a broad range of animals has allowed to trace the evolution of developmental and neuronal characters on a better-resolved animal phylogeny. This has falsified most traditional scenarios for nervous system evolution, paving the way for the emergence of new testable hypotheses. Here we summarize recent progress in studies of nervous system development in major animal lineages and formulate some of the arising questions. In particular, we focus on how lineage analyses of nervous system development and a comparative study of the expression of neural-related genes has influenced our understanding of the evolution of an elaborated central nervous system in Bilateria. We argue that a phylogenyguided study of neural development combining thorough descriptive and functional analyses is key to establish more robust scenarios for the origin and evolution of animal nervous systems.

Automated summary

Biologists have long been fascinated by the evolution of nervous systems in animals, but traditional explanations have been limited by a lack of robust phylogenetic framework for animal interrelationships and understanding of developmental mechanisms. Recently, advancement in molecular and morphological studies has allowed for a clearer tracing of evolution of developmental and neuronal characters in a wide range of animals. This has led to the rejection of traditional scenarios and the emergence of new testable hypotheses in the evolution of animal nervous systems.