Emergence of Animals from Heat Engines. Part 1. Before the Snowball   Earths
  Previous studies modelled the origin of life and the emergence of photosynthesis on the early Earth-i.e. the origin of plants-in terms of biological heat engines that worked on thermal cycling caused by suspension in convecting water. In this new series of studies, heat engines using a more complex mechanism for thermal cycling are invoked to explain the origin of animals as well. Biological exploitation of the thermal gradient above a submarine hydrothermal vent is hypothesized, where a relaxation oscillation in the length of a protein 'thermotether' would have yielded the thermal cycling required for thermosynthesis. Such a thermal transition driven movement is not impeded by the low Reynolds number of a small scale. In the model the thermotether together with the protein export apparatus evolved into a 'flagellar proton pump' that turned into today's bacterial flagellar motor after the acquisition of the proton-pumping respiratory chain. The flagellar pump resembles Feynman's ratchet, and the 'flagellar computer' that implements chemotaxis a Turing machine: the stator would have functioned as Turing's paper tape and the stator's proton-transferring subunits with their variable conformation as the symbols on the tape. The existence of a cellular control centre in the cilium of the eukaryotic cell is proposed that would have evolved from the prokaryotic flagellar computer. 
Anthonie W.J. Muller