[acjohnson55]

I would actually invert that and say that melody and rhythm are the most fundamental aspects of music. A harmonic progression with no sense of melody or rhythm is quite boring.

Harmony is derived from composing music with multiple melodic parts. This is most obvious with counterpoint, but even pop/rock music can be seen this way. The essence of pop/rock is a melody and bass line as the two primary parts, and the rest of the instrumentation often plays harmonies that imply inner voices.