Why do not human being use pitch to communicate?

All the langaugages employ different acoustic signal to encode their information or semantic. They can be categorized into segmental,e.g. consonatnt and vowel, and supra-segmental,e.g.tone and stress. So the linguists define nontonal languages, such as most Werstern languages and tonal languages, for example, Chinese, Vietnamese,Thai. However, the latter languages must use constant and vowel as well as tone. We cannot found a pure tone language or a pure stress langauge.

Crosspendantly, the listener could recognize and discriminate these sounds by its acoustic cues.In speech perception, the psycholinguist sumaries different cues and arrange them into a hireachy system(Liu & Samuel, 2004). In acoustic, any sound can be analyzed into frequency, wavelength, period, amplitude and velocity or speed. Tone is dominated by pitch's frenquecy.However, vowel and consonant are dominated by

Why do human being not use pitch or tone to communicate? This is a very intresting question. Can you image there was a group of people chat with each other like dophine in sea.