Final answer:
The earliest type of polyphonic compositions from around 900 A.D. are called organum. These began to develop during the high medieval era, and the Renaissance saw further evolution in polyphonic music with smoother textures and increased vocal ranges.
Step-by-step explanation:
The earliest type of polyphonic compositions, dating from around 900 A.D., are called organum. Polyphony is an important musical texture that consists of two or more simultaneous lines of independent melody, as opposed to a single melodic line in monophonic music. The development of polyphony began during the high medieval era and became more prevalent during the thirteenth and early fourteenth century, a time often associated with the Ars nova.
Different types of polyphonic music emerged over time, including masses, motets, madrigals, and chansons, among others. In the Renaissance, polyphony evolved further as musical composition began to include the interval of the third, which was previously considered a dissonance during the Middle Ages. This era saw an increase in the vocal range used in music and a simplification of textures, aiming for smoothness in the contrapuntal parts.
The theory and notation of music also developed during the Medieval period, laying the foundation for Western music and including advances in rhythm and polyphony.