Researchers infer that mankind discovered cooking ~1.9 million years ago - based on studies of our molar teeth.
Most large animals chew extensively so its easy to swallow. Cooking softens the food and dramatically reduces eating time to about 5% of the day (compared to ~48% if we didn't). Softer food due to cooking helped us evolve smaller molars and smaller jaws - a little less than 2 million years ago.
