(Excerpts discussion for one of eleven features of jazz, examined to answer the question What Is European & What is African?)
Improvisation
The first feature of jazz we are going to examine is improvisation, the practice of spontaneously varying individual parts. It has been an important element of music since the beginning of time, and only recently in history was it difficult to find in European concert music. Improvisation characterizes some African music and much jazz. Musicologists are uncertain about the extent to which African American music retained improvisatory traditions from 
African music. Let’s first consider improvisation in music of cultures that contributed slaves to the New World. For instance, in the typical drum ensemble of Ghana, the lead drummer is in charge of giving signals. His part is more variable than any of the others, so it might be regarded as improvised. In the Mandinka drum ensemble, the senior player has leeway to improvise more than the others, but all members are allowed to slightly vary their parts as they play. Some African singing in leader-and-chorus format allows spontaneous variations in the leader’s part, as in “Hunter’s Dance” in the Jazz Classics CDs. To keep this in perspective, we must note, however, that these practices come nowhere near the extent of improvisation that is found today in jazz. In West African singing and the African American blues that evolved from it, improvisations did not consist of inventing elaborate melody lines as eventually became common for jazz improvisers. Instead, these singers channeled their creativity into altering the sound of a single sustained tone, varying the timing, pitch, and timbre at its beginning and ending. They also improvised by toying with the rhythms of melodies. Tones would be started a bit earlier or later. Or a given tone might be repeated several times in succession instead of being sung only once. Similarly, a tone might be started, then softened, and then pushed again by an abrupt increase in volume. Sometimes whole phrases would be placed differently in relation to the underlying beat. This is known as rhythmic displacement. Incidentally, these techniques are still evident in performances of gospel music by African American singers and in gospel-influenced styles of pop music, such as the singing of Aretha Franklin and James Brown. (These practices are evident in the three samples of vocal music at the beginning of the Jazz Classics CDs.)
The reason we discuss singing at this point in a textbook about instrumental jazz is that these vocal practices are thought to have influenced the styles used by jazz musicians who played trumpet, trombone, clarinet, and saxophone. (That is why the beginning of the Jazz Classics CDs has an instrumental demonstration by Miles Davis directly following the cry of the African American street vendor.) Individual creativity and unorthodox means for learning how to play instruments have also been suggested as roots for pitch and timbre improvisation in horn work. Some musicologists believe that demand for live music was so great in New Orleans that many unpolished amateurs were called upon to perform as professionals, and the incomplete mastery these players had over their instruments gave us the collection of raw, unorthodox sounds we now associate with New Orleans jazz. Imitation of singing style, however, is the most popular explanation among musicologists. In addition, some scholars believe that the spirit of improvisation and the stress on individuality in jazz stem from African traditions. But these traits are also found in America within non-African folk music as well. So a striving for individuality among jazz musicians could be, but is not necessarily or exclusively, an extension of African preferences or what has been called “the black esthetic.”
Now let’s consider what European music could have contributed to the origins of improvisation in jazz. In America there was already a well-developed European tradition for improvising by the time jazz had begun. Improvised ornaments were common in pre-twentieth-century concert music, and they have long been common in folk music and popular music. Within informal American music prior to the emergence of jazz, there are also precedents for improvisation in the form of musicians making spontaneously varied entrances. Often singers start notes whenever they feel like it instead of singing precisely in unison with the others. This is termed heterophony, sounding to our ears like ensemble “sloppiness.” It is also notable that improvised variations were common parts of solo recital format for some keyboard artists. During the 1800s, concert pianists often improvised within the encore number of their program. And there existed a French and German keyboard tradition for improvisation called preluding. Some early American musicians were even required to be able to improvise a piece on demand, using phrases supplied by their audience. So it is clear that the practice of making up music as you go along is precedented in both West African and European music. Both of these traditions could have influenced the use of improvisation in jazz.
Now consider improvisation among New Orleans musicians at the beginning of the twentieth century. At least as late as 1923, the improvisational creativity of the players was directed primarily at piecing together band routines. Some routines, however, were spontaneously devised during performances, thereby qualifying as improvised. The skeletons for these routines were often provided by published arrangements that were known among musicians as “stocks.” For the first few run-throughs, many of the parts were not fixed. Trombone counterlines, clarinet obbligatos, and trumpet variations of the melody were sometimes invented and performed spontaneously. Accompaniments were improvised and varied by the more adventurous and creative players. After a suitable set of parts had been worked out, the musicians frequently remained relatively loyal to them. A striving for improvisation was not as central to a jazz esthetic as it has become. The extent to which new melodies were freshly improvised during performance was limited. There was, however, a striving for personalization and individualization which did not require improvisation, at least in the sense that the term is used here. Though the seeds were planted in New Orleans, it is possible that the kind and the extent of jazz improvisation known today did not first emerge there.
By the late 1920s, these improvisational tendencies had expanded to the extent of improvisation we ordinarily expect from most jazz today. Unfortunately, we will never know why this change occurred. The possible reasons include 1) boredom with fixed routines; 2) a need to learn new material without recourse to sheet music; 3) increased interest in bravura solo excursions and emergence of the “star” system of players; 4) a continuation of European and/or African traditions for spontaneous alteration; 5) unbridled creativity; 6) longer dances necessitating stretching out the numbers, that, in turn, led to solos that give other hornmen time to rest their lips; and 7) a combination of these reasons.
Excerpted from the chapter “Origins of Jazz.”