when and where have human beings started to make vocal harmonies?

when and where have human beings started to make vocal harmonies?

Last day, suddenly I came up the idea about, "when and where have human beings started to make vocal harmonies? "so I have started researching this.I thought it was easy to get this, but never thought that music and human history were so deep and mysterious.Many difficult music terminology, world history, ancient history, and ethnic music of the world,,,, there were so many things that I had to...