Music has played a large part in human society for over 4000 years. Today, due to varying cultures and geographical regions, many different types of music exist, separated loosely into genres. According to Peter van der Merwe, a musical genre is "a category of pieces of music that share a certain style or 'basic musical language.' " Ever since Rock and Roll evolved in the 1940's from Blues and Country music, it has remained America's number one choice in musical style. Music is sold in many different formats and enjoyed by people of all ages.