How did click sounds spread from Khoisan languages into Bantu languages?

Click sounds spread from Khoisan languages into various Bantu languages through long-term cultural and linguistic contact. As these groups interacted, the Bantu languages—which are not originally "click languages"—borrowed these distinctive consonants, incorporating them into their own phonological systems.12

The extent of this borrowing varies by language. For example, Zulu and Xhosa have incorporated three click sounds into their consonant systems. Other Bantu languages, such as Gciriku and Yei in Botswana and Namibia, have adopted a more extensive four-click system derived from the Khoisan languages.231

This process of linguistic influence occurred as Khoisan speakers interacted with dominant neighboring groups, leaving a lasting mark on the sound structures of languages like Xhosa, Zulu, and Sotho. While these Bantu languages are now considered "full-fledged" click languages, they are categorized as such only derivatively, as the clicks were acquired through contact rather than inherited from a common ancestral language.142