I highly recommend The Unfolding of Language by Guy Deutscher, which was supplementary reading for the IS Group meeting held on Nov. 17, 2007. Quoting from the epilogue:
"... complex linguistic structures can arise through the natural forces that are changing language, even today. The elaborate conventions of language needed no gifted inventor to conceive them, no prehistoric assembly of elders to decree their shape, nor even an overseer to guide their construction. ... Behind the forces of change there are always people -- the speakers of a language. ... language change joins a long list of phenomena ... which are brought about through people's actions, but are not willfully intended by them. The transformations in language ... emerge from ... spontaneous and immediate concerns, such as saving effort in pronunciation (economy) or the desire to heighten the effect of an utterance (expressiveness). ... The accumulated pressure of such spontaneous actions nonetheless creates powerful and untiring forces of change: the flow towards abstraction, and erosion in meaning and sounds. The combination of these forces operates on language like a relentless bleaching and compressing machine. ... Language is a tool that has been worn into shape by continual use."