It’s Time to Defuse the Cambrian “Explosion”

Abstract

Volcanoes may erupt explosively. Meteoroids may explode on entering the atmosphere. A microwaved grape may explode (Conover, 2019). However, a growing body of research suggests that biodiversity at the dawn of the Cambrian Period did not explode. Data, amassed in the century and a half since Charles Darwin (1859) agonized that the apparent absence of Precambrian lifeforms was the weakest link in his theory of evolution by natural selection, support the view that biological diversity at the beginning of the Cambrian Period did not burst violently, detonate, shatter, or blow up. In this contribution, we trace the origin of the phrase "Cambrian explosion," give reasons for moving away from using it, and offer an alternative for describing intervals of significant increase in the diversity of life. The bibliographic pedigree of the phrase "Cambrian explosion" is uncertain; its origin is not clearly established in peer-reviewed literature. By the early twentieth century, the abrupt appearance of abundant (macro-) fossils in the Cambrian was canon in historical geology textbooks (Schuchert and Dunbar, 1933). The earliest use of the adjective "explosive," with reference to an evolutionary rate, was likely George Gaylord Simpson's "explosive evolution" to describe a general pattern of rapid diversification early in the history of a lineage (Simpson, 1944). Mid-twentiethcentury contemporaries echoed use of this phrase in characterizing a general evolutionary pattern (Henbest, 1952; Colbert, 1953). Use of the phrase "explosive evolution" to describe rapid diversification during the early Cambrian morphed into "The Cambrian Explosion" under obscure circumstances. The earliest published occurrence known to us is a section heading in an early version of an experimental high school biology curriculum

Palaeoecology of Cambrian–Ordovician acritarchs from China: evidence for a progressive invasion of the marine habitats

“…The major evolution event, extensively documented as the Cambrian ‘explosion’, is largely known also by a wider public, although different concepts and definition of the term exist. Today it becomes clear that the ‘sudden’ occurrence of all phyla was most probably not ‘explosive’ but took place over several tens of millions of years, and the term ‘explosion’ is clearly misleading [35].…”