Origins and Early Evolution of Predation

Abstract

Predation, in the broad sense of an organism killing another organism for nutritional purposes, is probably as old as life itself and has originated many times during the history of life. Although little of the beginnings is caught in the fossil record, observations in the rock record and theoretical considerations suggest that predation played a crucial role in some of the major transitions in evolution. The origin of eukaryotic cells, poorly constrained to about 2.7 Ga by geochemical evidence, was most likely the ultimate result of predation among prokaryotes. Multicellularity (or syncytiality), as a means of acquiring larger size, is visible in the fossil record soon after 2 Ga and is likely to have been mainly a response to selective pressure from predation among protists. The appearance of mobile predators on bacteria and protists may date back as far as 2 Ga or it may be not much older than the Cambrian explosion, or about 600 Ma. The combined indications from the decline of stromatolites and the diversification of acritarchs, however, suggest that such predation may have begun around 1 Ga. The Cambrian explosion, culminating around 550 Ma, represents the transition from simple, mostly microbial, ecosystems to ones with complex food webs and second- and higher-order consumers. Macrophagous predators were involved from the beginning, but it is not clear whether they originated in the plankton or in the benthos. Although predation was a decisive selective force in the Cambrian explosion, it was a shaper rather than a trigger of this evolutionary event.