Music is an art form whose medium is sound and silence. Its common elements are pitch (which governs melody and harmony), rhythm (and its associated concepts tempo, meter, and articulation), dynamics, and the sonic qualities of timbre and texture. Music is found in every known culture, past and present, varying wildly between times and places. Since all people of the world, including the most isolated tribal groups, have a form of music, it may be concluded that music is likely to have been present in the ancestral population prior to the dispersal of humans around the world. Music may thus have been in existence for at least 50,000 years, and the first music may have been invented in Africa and then evolved to become a fundamental constituent of human life. A culture's music is influenced by all other aspects of that culture, including social and economic organization and experience, climate, and access to technology.