In the early times when human beings hunted and gathered food, they were not in control of their environment. They could only interact with their surroundings as the other lower animals did.
　　When they learned to make fire, however, they became capable of altering their environment. To provide themselves with fuel, they cut down trees. They also burned clearings in forests to increase the growth of grass and to provide a greater grazing area for the wild animals that human beings fed upon. This development led to farming and the domestication of animals. Fire provided the means for cooking plants which had previously been inedible. Only when the process of meeting the basic need for food reached a certain level was it possible for humans to follow other pursuits such as setting up families, forming societies and founding cities.