I wonder why tonal language ever evolved.
It doesn't seem to make any sense to have the same words mean different things if you can just make a different word...
It doesn't seem to make any sense to have the same words mean different things if you can just make a different word...
Sarcasm aside though, a whole lot of languages are tonal. Most languages spoken in Asia and many African ones are. And you use tone too: what's the difference between "You there." and "You there?" and "You there!". It just serves a different purpose in English than it does in Chinese so it seems less mysterious to an English speaker.
The only tonal language I can really speak about is Mandarin (although I encourage you to read about other systems). The way the tones work in Mandarin isn't as complicated as it sounds. The classic example is this[1]:
1. mā (妈, mother). This sounds like a somewhat high-pitched, steady tone
2. má (麻, hemp). This is called a rising tone, and it sounds sort of like the end of a question in English
3. mǎ (马, horse). This tone falls and then rises (sort of like a #4 then a #2). Imagine a whiny child saying "mooooom!" to get their mom's attention
4. mà (骂, scold). This tone falls quickly, it sounds like in the movies when someone shouts "Hey!" at a robber that's getting away
5. ma (吗, an interrogative particle). This is a neutral tone, its sound depends mostly on the syllable before it but in isolation it either falls slightly or sounds like an English "toneless" syllable.
Mandarin only has those 5 tones, it's not like "ma" can sound fifteen different ways. They aren't differentiated by the pitch itself exactly, it's whether the pitch is rising or falling.
A Chinese speaker might describe the difference between má and mà the same way you'd describe the difference between "bet" and "bit" to a speaker of a language that doesn't differentiate those vowels. Sort of like rhyming, but not quite. As an easier example, Spanish doesn't really have a contrastive /ɪ/ as in "bit", so a Spanish speaker might have the same trouble differentiating or producing it without some practise that you might have doing the same to má or mǎ.
[1] https://en.wikipedia.org/wiki/Tone_(linguistics)#Mechanics
It's the other way around: http://wals.info/feature/13A#2/28.6/152.8
Is Chinese missing vowels?
Usually complexity increases because it confers some kind of evolutionary advantage.
Language doesn't follow the same rules as biological evolution. For instance, prestige dialects often cause people to opt to use a less useful language for social status reasons. Pidgins can create amalgamated languages with essentially random features of the parent languages. Many language changes really confer no "benefit" at all, like a change from agglutination to strict word order (and back again).
And there is some evidence that there have been shifts in tonal complexity within languages over time [3].
[1] https://www.mpg.de/8879447/tonal-languages-institutes
One you have "just" made your different words, then you can "just" teach them to one billion or so people, and you are done.
What does make sense is that languages evolved over long periods of time. People didn't "just" make different words that everyone suddenly used. Just as English has "digest your food" and "Reader's Digest" with different intonation, Chinese distinguishes meanings and words with different intonation as well. Not exactly the same because there's also a difference in the written form in most cases. It doesn't have to make sense... it just is.