Function, chance and purpose in the biosphere: a critical examination of the Darwinized Gaia hypothesis

The original Gaia hypothesis purports to explain the long-term maintenance of the Earth's habitability by proposing that the biosphere has evolved homeostatic control of environmental parameters crucial to its survival. This idea was criticized for being incompatible with core Darwinian requirements for evolution by natural selection, since the biosphere is not part of a population of entities with variation, reproduction and heredity. Recently, however, some authors have defended a 'Darwinized' version of the Gaia hypothesis. Proponents of Darwinized Gaia argue that there can be natural selection for persistence alone, with no need for reproduction or competition, and that a single lineage can undergo a process of sequential selection over time. This article examines these ideas in the light of two important distinctions in evolutionary biology: adaptation versus by-product, and transformational versus variational explanation. Despite these new interesting ideas, however, the Darwinized Gaia hypothesis still cannot overcome the main objections from evolutionary biology.This article is part of the discussion meeting issue 'Chance and purpose in the evolution of biospheres'.