Catherine Zink and Daniel Lieberman have a research paper you science nerds might be interested in. A teaser:
“Yet Homo erectus differs from earlier hominins in having relatively smaller teeth, reduced chewing muscles, weaker maximum bite force capabilities, and a relatively smaller gut. This paradoxical combination of increased energy demands along with decreased masticatory and digestive capacities is hypothesized to have been made possible by adding meat to the diet, by mechanically processing food using stone tools, or by cooking. Cooking, however, was apparently uncommon until 500,000 years ago.
Source: Impact of meat and Lower Palaeolithic food processing techniques on chewing in humans : Nature : Nature Publishing Group