Events in Early Nervous System Evolution.

We propose that neurons and nervous systems evolved among thin, motile, microbe-eating animals during the Ediacaran period (635-543 million years ago). Spiking neurons evolved from epithelial cells around the margins of Ediacaran microbial mat grazers that initially specialized to detect weak bioelectric fields of nearby animals and to trigger rapid withdrawal movements. According to this scenario, nervous systems are a consequence of two preceding animal innovations, external digestion and motility, which have co-evolved in concert with nervous systems ever since. We suggest that fundamental characteristics of modern nervous systems can be explained by studying how nervous systems originated during the Ediacaran period, as natural computers for predictive statistical inference given event-based sense data.