Question

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, or central, idea of the passage?
early humans ate uncooked meats and vegetables, so they needed strong jaws for chewing.
as early humans developed agriculture, their bones changed significantly.

Explanation:

The passage first describes early ancestors as hunter - gatherers with strong bones (including jaws) for eating tough, uncooked food. Then it states that when agriculture was developed (diet change - cooking food, softer food, less active lifestyle), the human skeleton (jaw became smaller, other bones lighter) underwent radical changes. The first option only focuses on the early, pre - agriculture situation. The second option encompasses the cause (agriculture development) and the effect (bone changes), which is the main idea.

Answer:

As early humans developed agriculture, their bones changed significantly.