Khoisan people from South Africa spoke the !Kung language. It is probably the closest we can come to what the earliest languages sounded like. !Kung is a click language. The ! in the name of the language represents a clicking sound that !Kung speakers make with their tongue.
Of all the languages in the world, !Kung has the largest number of different kinds of sounds. Generally, the further you live from South Africa, the fewer different sounds there are in your language, as if people gradually simplified their sounds as they travelled further away. (Hawaiian has the smallest number.)
When Bantu people moved into South Africa, many people who spoke !Kung began to speak Bantu instead. And a lot of Bantu people began to mix !Kung words into their language, creating new languages called Xhosa and Zulu.