Most "primitive" music is so-called "two-phrase" music - basically a call phrase and a response phrase, or a question and an answer. This simple musical form exists across cultures, in nursery rhymes, and in basic karimba music.
Sometime between 600 and 1000 years ago in the Zambezi Valley of southeastern Africa - let's suppose during the peak of the "Great Zimbabwe" civilization - an incredible innovation occurred: that primal two-phrase tune pattern evolved into a "four-phrase" pattern. This innovation was momentous. Doubling the length of the original two-phrase cycle had the effect of expanding the possibilities of the music by far more than a factor of two. This four-phrase musical structure is the essence of the sound of the mbira. It is one of the pinnacles of African music, culture and intellect.
In this post I will impart my conceptualization of an essential African musical form to you, and will start with the basic chord progression common to a lot of four-phrase mbira music. This harmonic understanding, which can be applied to any instrument, will be demonstrated on guitar in the keys of G and A.