Catching Fire: How Cooking Made Us Human by Richard Wrangham. This book argues that the ease of digestion and the added nutritional value available in cooked food was the key behind the explosion of human intelligence. (Cooking gelatinizes starch, denatures protein, and softens all foods, permitting more complete digestion and energy extraction. As a result, the food processing apparatus shrinks, freeing energy to support a larger brain.) He then suggests that cooking led to what eventually became marriage and the sexual division of labor. The two most helpful reviews at Amazon get into great detail. The reviews average to 4+ stars.