The history of music in relation to human beings predates the written word and is tied to the development and unique expression of various human cultures. Music has influenced man, and vice versa, since the dawn of civilization. The earliest form of musical expression is to be found in the Sama Veda of India. Popular styles of music varied widely from culture to culture, and from period to period. Different cultures emphasized different instruments, or techniques. Music history itself is the distinct subfield of musicology and history, which studies the chronological development of music, primarily in the Western world. Music has also been used extensively for propaganda. As there are many definitions for music there are many divisions and groupings of music, many of which are caught up in the argument over the definition of music. Among the larger genres are classical music, popular music or commercial music (including rock and roll), country music and folk music. There is often disagreement over what constitutes "real" music: late-period Beethoven string quartets, Stravinsky ballet scores, serialism, bebop-era Jazz, rap, punk rock, and electronica have all been considered non-music by some critics when they were first introduced. The term world music has been applied to a wide range of music made outside of Europe and European influence, although its initial application, in the context of the World Music Program at Wesleyan University, was as a term including all possible music genres, including European traditions. (In academic circles, the original term for the study of world music, "comparative musicology", was replaced in the middle of the twentieth century by "ethnomusicology", which is still an unsatisfactory coinage.) Genres of music are as often determined by tradition and presentation as by the actual music. While most classical music is acoustic and meant to be performed by individuals or groups, many works described as "classical" include samples or tape, or are mechanical. Some works, like Gershwin's Rhapsody in Blue, are claimed by both jazz and classical music. As world cultures have been in greater contact, their indigenous musical styles have often merged into new styles. For example, the United States bluegrass style contains elements from Anglo-Irish, Scottish, Irish, German and some African-American instrumental and vocal traditions, which were able to fuse in the US' multi-ethnic "melting pot" society. Many current music festivals celebrate a particular musical genre.