Instead of diving right into the history of mankind's development, the book begins by looking at how modern humans do on a raw food diet. There are many people who swear by eating food that is either raw or cooked at very low temperatures. Studies have found that while subjects have eaten the same amount of calories as their cooking counterparts, they loose weight. Part of the explanation is that heating food breaks some of the bonds that hold substances together on a molecular level. Because those bonds are softened or broken by cooking, it is easier for the digestive system to extract the calories.
By looking into modern hunter/gatherer societies, Wrangham sees social benefits to the division of labor, men hunting woman gathering and cooking, that add up to better survival chances for our proto-human ancestors. By cooking food, less energy was needed for digestion, creating smaller guts and spare resources for brain development. Paired women could count on the protection of their food by their hungry partners.
Chimps and great apes chew the raw food that is available to them for almost six hours per day. That much mastication takes time away from hunting. Modern man chews for an average of an hour to an hour and a half per day leaving lots of room for other tasks.
The book makes lot more points and it is a fascinating take on evolution and what separated humans from other animals.