The Cronus Hypothesis - extinction as a necessary and dynamic balance to evolutionary diversification

Abstract

The incredible diversity of life on Earth veils the tumultuous history of biodiversity loss over deep time. Six mass extinction events since the Cambrian species explosion (including the current Anthropocene), and many smaller extinction spasms, have terminated 99% of all species that have ever existed. Evolution and extinction, as universal processes, have been unified previously under James Lovelock's Gaia hypothesis, and most recently, under Peter Ward's Medea hypothesis. Gaia (the Greek Earth mother) posits that life on Earth functions like a single, self-regulating organism, whereas Medea (siblicidal wife of Jason of the Argonauts) describes instead a self-destructive feedback where life "seeks" to destroy itself. We argue that these contrasting views are actually extremes of a scale-invariant stability entropy spectrum of speciation and extinction for all life on Earth, much as the abundance and stability of a metapopulation of an individual species is the emergent property of births, deaths and migration. In this context, we propose a new metaphor called the Cronus hypothesis (patricidal son of Gaia) to explain how these processes can be quantified with existing mathematical tools and so be used to describe the ebb and flow of life on Earth along a thermodynamic spectrum. We also argue that Cronus provides a broader framework with which to link the natural history research domains of evolutionary, ecological and extinction biology.