In the more ancient stone age pre-history, people lived in "tribes" and lived in caves or tents made from animal skin. They had simple tools made from wood and bones, and cutting tools from stone such as flint, which they used to hunt and to make simple things. They made fire and used it for cooking and to stay warm. They made clothing out of animal skins, and later by weaving. Society started when people began doing specialized jobs. This is called the division of labour. The division of labor made people depend on one another and led to more complex civilizations.