When early humans hunted and gathered food, they were not in control of their environment. They could only interact with their surroundings as lower organisms did. When humans learned to make fire, however, they became capable of altering or changing their environment. To provide themselves with fuel they stripped bark from trees, causing the trees to die. Clearings were burned in forests to increase the growth of grass and to provide a greater grazing area fro the wild animals that humans fed upon. This development led to farming and the domestication of animals. Fire also provided the means for cooking plants which has previously been inedible. Only when the process of meeting the basic need for food reached a certain level of sophistication was it possible for humans to follow other pursuits such as the founding of cities. According to the passage, early humans gained better control of their environment when they learned to .