Mariachi giving them modified shapes and tunings. In addition to instruments, the Spanish introduced the concept of musical groups—which, in the colonial period, generally consisted of two violins, a harp, and various guitars. This grouping gave rise to a number of folk musical styles in Mexico. One of these folk musical styles was the "son". This music featured string instruments. "Son" music divided into various regional varieties—the variety popular in the Jalisco area was called "son jalisciense", whose best known song, also referred to as "the mariachi national anthem," is “La Negra.” Modern mariachi music developed from this "son" style, with
Mariachi problems recruiting mariachi instructors as many of these do not have required teaching credentials. For this reason, schools often hire trained musicians from outside the mariachi tradition. Many traditional mariachis are concerned that standardization will lead to fossilization and restrict improvisation. Other innovations in the United States have been the incorporation of styles of artists such as Elvis Presley, Freddy Fender and Glenn Miller, as well as the heavy-metal Mariachi band Metalachi. Another is the encouragement of female mariachis including all-female Mariachi groups such as Mariachi Mujer 2000 and Mariachi Divas de Cindy Shea. Mariachi Mujer has performed with Mexican