Via Panda's Thumb, P.Z. Meyers reviews the evolution of the senses. Our senses of sight, taste and smell (and also some pheremone responses) all first register items in the environment via a closely related set of proteins called G-protein coupled receptors. It turns out that this family is very ancient, and also occurs in bacteria. Other senses, namely hearing, touch, and balance,l register at the cell level when physical shearing of the cell surfacel activates a family of proteins known in mammals as TRP channels.
The new work discussed by Meyers, which appeared in Nature a while back, describes an ancient pedigree for the TRP-like channels as well. There are fungal and bacterial proteins which also register physical stress at the cell surface, and some are direct homologs to the mammalian proteins.
The hypothesis of the review is that bacteria evolved G-protein coupled channels to detect soluble items in their surround, and mechanosensory channels to detect physical stress. These inventions, once established, became highly portable widgets to solve a large number of sensory problems. Truly a great demonstration of the Panda's Thumb principle-- that natural selection tweaks working solutions rather than designing anew.