>>18244822
In the particular case of Chinese, it seems to be a regional feature of Southeast Asia. In the general case: Look up "tonogenesis". Basically tl;dr: sometimes another phonetic distinction will incidentally lead to differences in pitch, and then when it drops off the pitch will be the only distinction left. For example, if you listen to how people say them in ordinary speech, the word "sip" (which begins with a consonant that's pronounced with the vocal cords NOT vibrating) is usually pronounced with slightly higher pitch than the word "zip" (which begins with a consonant that's pronounced WITH the vocal cords vibrating, but otherwise the same). If the distinction between the vocal-cords-vibrating ("voiced") and vocal-cords-not-vibrating ("voiceless") consonants were dropped, the pitch would be the only thing left to distinguish them. In the particular case of Chinese, they seem to have originated from consonants at the ends of words that were dropped.

>>18244822

> they didn’t originate in China

In linguistics (from what I’ve been exposed to in my degree program, of course), African and Asian tone systems are treated differently. African tone systems mostly consist of single high, low, or rising/falling tones that keep their pitch quality throughout the entire phoneme, while Asian tones, often called contour tones, mostly use tones which change pitch values on the same phoneme (like the five tones of Chinese have rising, falling, and fall-rise tones)

>>18244822
words becoming homophones led to people trying to distinguish them somehow

>>18245679
No.

>>18245251
This. Some linguists argue Blacks are starting to do this since they drop so many consonants. See for example how blacks says cube and cute, both pronounced "kew", but in the case of cube it's a neutral pitch and cute has a rising pitch