The Deep Evolutionary Roots of the Nervous System

The evolutionary success of animals can, at least in part, be attributed to the presence of neurons that allow long-distance communication between tissues, coordination of movements, and the capacity for learning. However, the evolutionary origin and relationship of neurons to other cell types are fundamental questions that remain unsolved. The first neurons probably evolved shortly after the rise of the first animals over 600 million years ago. Studies on early-diverging animal lineages have provided key insights into the mechanisms underlying the origin of neurons. Recent discoveries in morphology, molecular signatures, and function of neurons in cnidarians and comb jellies, as well as neuron-like cells in nerveless placozoans, sponges, and other eukaryotes, may prompt a redefinition of what constitutes a neuron. Here we review the latest insights into the origin of neurons and nervous systems, while also highlighting exciting technological advancements that not only are accelerating our understanding of nervous system evolution, morphology, and function but also hold the potential to revolutionize the field.