Is Gaia alive? The future of a symbiotic planet

Life affecting first the development of the planetary environment, which, in turn, affects the future evolution of life in a coevolutionary way is a well-established idea now. Nevertheless, with the proposal of the Gaia hypothesis, there has been widespread criticism of some of its elements. Most critiques are related to teleology, the absence of natural selection at a universal scale, and the absence of planetary reproduction. Even if some of the problems concerning the rationale of this hypothesis have been resolved, it is not clear whether Earth can be considered a unit of selection and, therefore, Gaia can adapt according to Darwinian evolution. After Lovelock and Margulis, Gaia has been considered a symbiotic planet composed of biotic (the biosphere) and abiotic (the geosphere-atmosphere) interacting with and coevolving elements. Here, I took into consideration the main concerns raised on the Gaia hypothesis and I analysed them following a logic-deductive reasoning together with thought experiments, sometimes adopting analogical arguments. I propose why and suggest how, a Gaian system, considered as a “symbiotic planet” composed by biotic (the biosphere) and abiotic (the geosphere-atmosphere) interacting and coevolving elements, should be considered alive in an evolutionary sense. I argue that, without invoking teleology, so without any foresight or planning, a Gaian planet can be considered the same as a coevolutionary system analogous to a multicellular body: a super-unit of selection. I describe different situations according to which “Gaia” is able to reproduce and to transfer her planetary genome to other uninhabited or inhabited planets. Then I show that Gaia can face exclusion-competition-coexistence states depending on the fitness of her biota compared to those of the other reproducing biospheres. This demonstrates that Gaia can reproduce and evolve in competition-cooperation with other planets. Some deep implications arise from these pieces of evidence in the light of the recent discovery of a new solar system with Earth-like planets.