The culture of Papua New Guinea is many-sided and complex. It is estimated that more than 7000 different cultural groups exist in Papua New Guinea, and most groups have their own language. Because of this diversity, in which they take pride, many different styles of cultural expression have emerged; each group has created its own expressive forms in art, dance, weaponry, costumes, singing, music, architecture and much more. To unify the nation, the language Tok Pisin, once called Neo-Melanesian (or Pidgin English) has evolved as the lingua franca — the medium through which diverse language groups are able to communicate with one another in Parliament, in the news media, and elsewhere. People typically live in villages or dispersed hamlets which rely on the subsistence farming of yams and taro. The principal livestock in traditional Papua New Guinea is the oceanic pig (Sus papuensis). History Traditions On the Sepik River, there is a world-renowned tradition of wood carving. These carvers create forms of plants or animals, because they believe these are their ancestor beings and because they feel they are beautiful. They also create traditional skull portraits. Also well represented in the collections of museums around the world is the Malagan art tradition of New Ireland. Even though sea shells are no longer the currency of Papua New Guinea - sea shells were abolished as currency in 1933 - this heritage is still present in local customs. In certain parts of the country a groom must bring a bride price to the wedding ceremony. In some cases this is paid in golden-edged clam shells. In other areas, a dowry is payable rather than bride price. These payments may take the form of shell money, food, pigs, cash, or other goods. In some parts of the New Guinea highlands, people engage in colorful local rituals that are called "sing-sings". They paint themselves and dress up with feathers, pearls and animal skins to represent birds, trees or mountain spirits. Sometimes an important event, such as a legendary battle, would be enacted at such a musical festival. Music Traditional music Christian missionaries disapproved of Papuan folk music throughout the colonial period of the country's history. Even after independence, the outside world knew little of the diverse peoples' traditional music genres. The first commercial release to see an international audience didn't occur until 1991 (see 1991 in music), when Mickey Hart's Voices of the Rainforest