The Gaia theory states that the whole surface layer of the globe, including organisms, atmosphere, hydrosphere and lithosphere, can be viewed as a self-evolving homeostatic system. Bacteria play a principal role in this formative process. This line of thinking should answer several questions: Is the biosphere simply a set of essentially selfish individuals, each testing its fitness? Is memory in the biosphere confined to genes? Is the composition of ecosystems and their behavior only kind of dynamic equilibrium? Or is there a huge amount of epigenetic information that enables organisms to interpret properly their situation and behave accordingly? It is suggested here that it is the information flow, rather than pure thermodynamics and natural selection, that enables living beings not only to "read" their environment, interpret their situation and behave accordingly to this understanding, but also to establish geophysiology, to become part of Gaia. This flow comprises genes as well as signals, diffusible as well as permanent. From an analogy with the situation in the multicellular organism, three types of information mediators inside the body of Gaia are suggested: ultrastructure, diffusible signals and gene flux. With a shared gene pool, intricate ultrastructure and quickly diffusible signals, it is legitimate to consider Gaia a superorganism with an ontogeny.

Centre for Theoretical Study Charles University Praha 1 Czech Republic

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Developmental plasticity of bacterial colonies and consortia in germ-free and gnotobiotic settings