Selection for Gaia across Multiple Scales

Recently postulated mechanisms and models can help explain the enduring ‘Gaia’ puzzle of environmental regulation mediated by life. Natural selection can produce nutrient recycling at local scales and regulation of heterogeneous environmental variables at ecosystem scales. However, global-scale environmental regulation involves a temporal and spatial decoupling of effects from actors that makes conventional evolutionary explanations problematic. Instead, global regulation can emerge by a process of ‘sequential selection’ in which systems that destabilize their environment are short-lived and result in extinctions and reorganizations until a stable attractor is found. Such persistence-enhancing properties can in turn increase the likelihood of acquiring further persistence-enhancing properties through ‘selection by survival alone’. Thus, Earth system feedbacks provide a filter for persistent combinations of macroevolutionary innovations. Doolittle has recently proposed that Gaia could have arisen through ‘selection by survival alone’ in which persistence of the biosphere increased its likelihood of acquiring further persistence-enhancing traits. Several recent models demonstrate ‘sequential selection’ for global environmental regulation, in which systems that destabilize their environment are short-lived and result in extinctions and reorganizations until a stable state is found. Evidence of microbial community coalescence provides a mechanism for heritability of ecosystems and their properties, making models of ecosystem-level selection for environmental regulation empirically plausible. The Black Queen hypothesis – that production of ‘leaky’ ecological public goods is lost until there is negative frequency-dependent selection on the remaining producers – can help to explain regulation, for example, of the marine nitrogen cycle.