Read the passage.
The Evolving Human Skeleton
Our early ancestors were hunter-gatherers who obtained food by hunting and by searching for edible wild plants. They needed strong bones, including large, strong jaws that enabled them to eat tough, uncooked foods. When our ancestors developed agriculture, however, their diet changed. They began growing plants, such as grains and beans, and raising animals for food; they also started cooking their foods, making them softer and easier to chew. Consequently, the human skeleton underwent radical changes. Over time, the human jaw became smaller and changed shape. Other bones also evolved, becoming lighter, especially in the joints, as a result of both dietary changes and a less active lifestyle.
What is the main idea of the passage?