You're begging the question. The "disparate impact in music" of blacks is the usual evidence offered by those who claim blacks are especially talented in this area in the first place. (Continue reading.)
An article from 1928 contains the following assessment of "the Negro's contribution to music":
the Negro made his greatest contribution both directly and indirectly in the field of the American folk song, "America's only indigenous music." These songs are relatively simple, with a highly restricted musical span, endless repetition, devoid of specific theme, childish, unfinished. Dr. E. B. Reuter in "The American Race Problem " devotes considerable space to the Negro and his musical abilities. Professor Reuter explains the evolution of the Negro minstrel and the metamorphosis of the character of the "darkey" who at first evoked sympathy to the later day city "coon," as an object of ridicule, "not of sympathetic interpretation." In like manner, the present-day ragtime and jazz music is fallaciously ascribed to the Negro. But this music "is primitive rather than African in origin." Perhaps because the Negro is adept at the peculiar gliding syncopations introduced with this new music or his slurring indistinguishable drawl, which seem a prerequisite of good jazz music, that he has been credited with its origin.Note: what concerns the sympathetic, Jewish author here is that "the Negro is discredited with music for which he is not responsible, and because of the handicaps of poverty and racial prejudice he is kept from the privileges of study and training necessary to fit him for fine, artistic production." Nowadays, of course, jazz is commonly viewed as the pinnacle of black musical achievement. It's all been downhill from there. William H. Youngren explains the origins of jazz as follows:
[Yale S. Nathanson. The Musical Ability of the Negro. Annals of the American Academy of Political and Social Science, Vol. 140, The American Negro (Nov., 1928), pp. 186-190]
When most people think of European music, they think of the concert (or "serious" or "classical") music of the past few centuries--dating back, say, to Bach, Handel, and Vivaldi. And certainly jazz does not sound like most of this music. It especially does not sound like the music of the composers we most often hear today in the concert hall: Beethoven, Wagner, Brahms, Tchaikovsky, Mahler, Debussy. What distinguishes jazz most sharply from the music of these composers and their contemporaries is that jazz has a firm and steady beat, kept by the drums and the other rhythm instruments. Jazz, as we know, originated as dance music, and all dance music needs a secure thythmic foundations to guide the dancers.(One theory of the etymology of "jazz": "I had heard that it was a derogatory term at first. White musicians heard it and called it jackass music. Jackass got shortened to Jass, and somewhere along the line, some one turned the s the other way and it became a z. And now you has jazz." This story is probably too good to be true -- it would be like finding out "rap" really is an abbreviation of "crap".)
The concert music of the last few centuries, however, is not the only sort of European music. Europeans, like Americans, developed their own characteristic forms of dance music, and when they emigrated to this country, they brought their dance music with them. One type that has grown popular in recent years is Jewish klezmer music--which, everyone has noticed, sounds remarkably like jazz. Recordings made in Europe in the 1920s and even earlier show that it sounded that way before jazz could possibly have influenced it directly. Anyone who has ever attended an Italian or a Polish wedding will have heard other sorts of ethnic dance music that also sound rather like jazz. One reason these ethnic dance musics sound like jazz is that they too, being music for dancing, have a steady beat. But there is another, far more important, reason.
Jazz, the various sorts of dance imported to this country from Europe, and the concert music of the last few centuries are all species of tonal music. That is, they are music written (or improvised) in a major or minor key, music organized according the system of major-minor harmonic tonality that gradually developed in ways that are still being debated, out of the modal music of the Middle Ages and the Renaissance and that became fully fixed in the early eighteenth century.
In the earliest jazz we can study closely, recorded jazz from 1917 on, the chord progressions that determine a melody's changing relation to the key of the piece are, roughly, those that were so used in the late eighteenth century, the time of Haydn and Mozart. Moreover, the phrases of the popular songs of the 1920s and earlier, which formed the basis for the vast majority of early recorded jazz performances, are similar in character to the phrases of late eighteenth-century music. [. . .] the various interrelated elements of early jazz--harmony, melody, rhythm, and form--are very similar to those of late eighteenth-century music and are in fact derived more or less directly from them, by way of the American popular song literature. [. . .]
That jazz was, from its beginnings, tonal music, and is therefore basically European or Western in nature, is so obvious that is should not need as labored a demonstration as I am giving here. The creators of jazz were, after all, men, most of them black but many of them white, who had been surrounded all their lives by tonal music--in church, in school, at parties, at celebrations on the village green. Moreover, the instruments they played--piano, violin, the various brass and woodwind instruments left over from Civil War bands--were constructed and tuned so as to produce the intervals and scales on which tonal music is based. [. . .]
In the recording he made for the Library of Congress in 1938, Jelly Roll Morton fondly recalls his visits to the French Opera House: "I remember the old building very well, there on Royal Street." And he plays the "Miserere" from Verdi's Il trovatore, first straight and then as he "transformed" it to jazz. "Jazz music is strictly music," he insists at one point. "you have the finest ideas from the greatest operas, symphonies, and overtures in jazz music. There's nothing finer than jazz music because it comes from everything of the finest class of music."
Morton certainly did not mean that jazz musicians should literally copy this or that classical piece--as some of them in fact were doing during the 1930s, when "swinging the classics" was all the rage. His stress on what he repeatedly called "transformation" and his proud claim that "I transformed every style to mine" suggest rather than jazz could benefit by borrowing, and adapting, techniques and turns of phrase from any worthy musical source. In the elaborately graceful melodic circumlocutions of both his published compositions and his improvised solos and backgrounds on his records, we can clearly hear the operatic airs and nineteenth-century salon pieces that lie behind them and that he undoubtedly played oftend during his early days, in the bordellos of Storyville. In the Library of Congres recordings he also claims to have "transformed" the different dances of an old quadrille into the successive strains of "Tiger Rag," and he plays the dances one after another: introduction, waltz, mazurka, "two-four time" (polka?), and so on. His claim was false: "Tiger Rag" was indeed based, at least in part, on an old quadrille, but it apparently had been worked out by a trombonist named Jack Carey. Nonetheless, Morton's mastery of the different dance forms, as well as their influence on his jazz playing and composition, is evident in his graceful, fluent performance.
In the eighteenth century, the German philospher Herder maintained that folksongs and folk poetry sprang spontaneously from the creative genius of an entire people. Historians have often represented jazz more as a product of the spirit of New Orleans blacks, the natural and inevitable expression of a particular Volksgeist, than a a musical style gradually and consciously developed by individual artists. From the beginning--or so the legend runs--jazz was collectively improvised, rather than composed and written down, because collective improvisation expressed the spontaneity and communal spirit that distinguished blacks from whites. The sensibility of the early jazz musician, the sort of figure long symbolized by the mysterious Buddy Bolden, was seen as having been shaped primarily by atavistic memories of African music and by direct experience of its American descendants: field hollers, country blues, work songs, and the like.
Yet the men who actually created jazz were not only surrounded from birth, as listeners, by Western tonal music; they also made their living by playing it. In the New Orleans of the 1890s, dance orchestras, both black and white, had to be able to play a variety of dances, waltzes, polkas, schottisches, mazurkas. As ragtime became popular, in the mid-1890s, these dances were joined by the two-step, which had become the dance that went with ragtime tunes, and which was itself edged out by the one-step about 1912.
Of course the black musicians of the 1890s and early 1900s recognized the differences between their ragtime or jazz numbers and the other sorts of dance music they played. But there is no evidence that they regarded jazz as superior, or improvisation as more "natural" to them as black musicians. In fact, jazz seems not to have been improvised at first--at least in the city of New Orleans, as distinguished from outlying rural areas. The members of the pre-1890 dance and brass bands in the city were trained musicians who could read music and were proud of it. In the mid-1890s, when some bands began to take in players who could not read and so preferred to improvise, these bands were looked down on and their music was spoken of scornfully, by the older, trained players, both black and white, as "head music" or "ratty music."
The emphasis laid by many writers on jazz's African origins has taught us to think of it as a rare and delicate hothouse plant, different in kind from the hardy indigineous growth surrounding it. The borrowings from other types of music that we have been tracing have therefore been regarded by jazz historians with suspicion. They have often voiced the fear that jazz would be (or already had been) tainted or distorted by non-African, specifically European, elements. This view appears in its most extreme form in Rudi Blesh's Shining Trumpets (1946). "The dilution and deformation of jazz," writes Blesh, "took place from 1920 on because of the influences of commercialism, white playing, and sophistication of the Negroes themselves." By the mid-1940s, Blesh felt, this process had "advanced to the point where the music frequently ceases to be predominantly a Negro form, becoming a hybridized popular music rather than a fine art form" (6).Today, the black genius for "borrowing" and "transforming" white music finds expression in such masterpieces as "Live Your Life (ft. Rihanna)" by T.I.: clearly it takes a uniquely African brand of creativity to even conceive of sampling the Numa Numa song -- and that's before we get to the lyrics.
Ever since jazz began to be taken seriously, the conviction that it either will be or already has been tainted or deformed has thus sent critics and historians off on a quest for the unadulterated archetype: absolutely pure black (which usually means New Orleans) jazz. Blesh rendered this goal by definition unattanable: since we have no black jazz recorded before 1920, all the jazz we can possibly know is already tainted. Other historians, less pessimistic, have claimed to find this perfectly pure black jazz in records by Armstrong or Morton or King Oliver. But it doesn't matter where they claimed to find it: it wasn't there. For the quest itself is misconcieved, and its goal is a chimera, a logical construction devised to justify a particular sort of musical taste. The music we call jazz has always been a "A hybridized poular music," developing in the midst of, borrowing from, and influencing other forms of popular music, including opera. [. . .]
Jazz's borrowings from other sorts of European music were the most natural thing in the world and should neither be wondered at nor deplored as signs of the dilution or deformation of a music once pure and perfect. Jazz was and is and always will be a hybrid, [. . .] No one creates music (or anything else) in a vacuum, ininfluenced by the world around him. [. . .] The fact that jazz was, from its beginings, the particular hybrid that it was and is merely follows from, and further confirms, its status as a member of the large family of tonally based European musics.
["European Roots of Jazz." The Oxford Companion to Jazz. Bill Kirchner (editor). pp. 17-28.]
Reuter (cited above by Nathanson) attributes the popularity of jazz to the "the slump of moral and aesthetic standards incident to the European War" and "the general lack of musical taste". The latter factor undoubtedly plays a major role in the popularity of black music down to the present.