This is where the debates really begin :) I think that most people who believe in some form of the motor theory of speech perception will also believe that spe

This is where the debates really begin :) I think that most people who believe in some form of the motor theory of speech perception will also believe that speech evolved from manual gesture. Others scoff at the motor theory. In fact, I'd say I'm in the minority by bringing it up with any regularity. If the question, what is "known" about the evolution of our ability to communicate, I wouldn't have much to point you towards. Most is theory based on modern evidence, somewhat like armchair psychology. Other people point to our ability to integrate non-verbal gestures into our comprehension, activation of our motor cortex prior to semantic/phonetic network activation when disambiguating difficult speech sounds, our ability to synthesize visual/auditory sources of information when the visual information relates to speech gestures (mouth/tongue movements), etc.