I believe that when human first stood erect, it changed human communication forever. Suddenly we stood face to face. Instead of relying on body language and words, humans looked eachother in they eyes and relied on them to communicate. suddenly looks mattered in the relationship, a pretty face to look at meant easier communication. kissing and smiling became ways to convey emotion. sadness and fear could be read thru they eyes and face. think about it, do any other mammals rely on facial gestures as much as we humans do???