That's a popular idea to throw around nowadays. Try body-languaging and voice-toning "excuse me, could you point me towards the nearest post-office?" to someone.
:-) :-) Not being a smartass and I'm sure I couldn't body language a "could you point me towards the nearest post office" to a total stranger, but my oldest son talked in sentences late and invented an elaborate system for communicating with me involving two word phrases, made up words, miming and grunting and gesturing. I finally stuck him in preschool to force him to use sentences, which I knew he could do but was refusing to do for some reason. Years later, when I was so ill and frequently in the midst of swallowing pills and thus unable to speak right at that moment, he was the only family member whom I could gesture and grunt at and usually get what I needed.
Language had to start somewhere. Presumably, it began with voice tone conveying important information, which is not terribly different from what most animals seem to do for communication.
Alright, you had some kind of primitive system for communicating certain "messages". It could be comparable to Morse code - two taps on the table means "me hungry", etc.
But I don't think that's related to people saying things like "70% of all communication is non-verbal". I just took it at face value, and tried to point out that it's not. It's just a comment that's tempting to throw around because it's kind of dramatic.
Instead of slapping an arbitrary percentage value on it, I'd be more comfortable saying "a considerable part of our communication is non-verbal", which it obviously is. 70% is just too high a percentage to be realistic.
Yes, language had to start somewhere, and because grunting and gesturing just isn't enough, it had to evolve to what we have now.