Cellular differentiation as a candidate “new technology” for the Cambrian Explosion

Almost all of the modern animal phyla appear to originate in a relatively compressed interval of time known as the Cambrian Explosion. Although several factors have been identified that may have enabled the Cambrian Explosion, there remains the question of the final trigger. The development of cellular differentiation, the capacity of a cellular lineage to become specialized permanently in response to external signals, is proposed as the trigger. Cnidaria and eukaryotic slime molds, which pre-date the Cambrian, have specialized cellular functions but their cells do not appear to differentiate irreversibly. With differentiation, cellular roles can be fixed during embryogenesis. Fixed cellular roles may have enabled more complex and more competitive organisms, perhaps by facilitating multi-scale structures in organs or increasing the stability and reliability of network systems including synaptic connections. A candidate evolutionary pathway to cellular differentiation is proposed. Introduction For reasons that have remained unclear, almost all of the modern animal phyla arrive in the fossil record during a geologically short period of about twenty million years, starting about 540-545 million years ago (Baker, 2006; Valentine, Jablonski, and Erwin, 1999). The Cambrian Explosion has been a unique and troubling anomaly in the history of life. Various attempts have been made to explain the Cambrian Explosion. Rapid change following a long period of quasi-stasis suggests the existence of a triggering or enabling event, either external to organisms or incorporated in organisms. It has been noted that the oxygen content of the atmosphere was slowly rising (Thomas, 1997). This was likely an enabler, and has been suggested as a trigger by Ohno (1997),