Because their food supply is far more reliable, pastoral societies can support larger populations. Since there are food surpluses, fewer people are needed to produce food. As a result, the division of labor (the specialization by individuals or groups in the performance of specific economic activities) becomes more complex. For example, some people become craftworkers, producing tools, weapons, and jewelry, among other items of value. The production of goods encourages trade. This trade helps to create inequality, as some families acquire more goods than others do. These families often gain power through their increased wealth. The passing on of property from one generation to another helps to centralize wealth and power. Over time emerge hereditary chieftainships, the typical form of government in pastoral societies. Horticultural Fruits and vegetables grown in garden plots that have been cleared from the jungle or forest provide the main source of food in a horticultural society. These societies have a level of technology and complexity similar to pastoral societies. Historians use the phrase Agricultural Revolution to refer to the technological changes that occurred as long as 10,000 years ago that led to cultivating crops and raising farm animals. Some horticultural groups use the slash-and-burn method to raise crops. The wild vegetation is cut and burned, and ashes are used as fertilizers. Horticulturists use human labor and simple tools to cultivate the land for one or more seasons. When the land becomes barren, horticulturists clear a new plot and leave the old plot to revert to its natural state. They may return to the original land several years later and begin the process again. By rotating their garden plots, horticulturists can stay in one area for a fairly long period of time. This allows them to build semipermanent or permanent villages. The size of a village's population depends on the amount of land available for farming; thus villages can range from as few as 30 people to as many as 2000. As with pastoral societies, surplus food leads to a more complex division of labor. Specialized roles in horticultural societies include craftspeople, shamans (religious leaders), and traders. This role specialization allows people to create a wide variety of artifacts. As in pastoral societies, surplus food can lead to inequalities in wealth and power within horticultural political systems, developed because of the settled nature of horticultural life. Agrarian Agrarian societies use agricultural technological advances to cultivate crops