Abstract

Animals pervade the modern biosphere and control how it works. Their unique combination of organ-grade multicellularity, motility and heterotrophic habit makes them powerful geobiological agents, imposing myriad feedbacks on nutrient cycling, productivity and environment. Most significantly, animals have ‘engineered’ the biosphere over evolutionary time, forcing the diversification of other organisms, of themselves, and indeed of the evolutionary process itself. This distinctively metazoan dynamic is readily recognizable in the Phanerozoic fossil record, but rapidly dissipates between 500 and 600 million years ago. The relatively belated appearance of animals is the focus of much speculation, with the effects of limited oxygen availability currently dominating most research agendas. I will argue here that such ‘permissive environment’ hypotheses fail to recognize the uniquely disruptive effects of even the simplest animals on environment, and that the evolution of multicellularity fundamentally enhanced oxygen availability to marine organisms through the invention of biologically mediated fluid flow – large-scale pumping, filtering and swimming. By extension, the convulsive biogeochemical and climatic perturbations of the late Proterozoic are more likely to be the consequences than the causes of early animal evolution.