The benefits of food processing: Processing food before eating likely played key role in human evolution -- ScienceDaily

"According to a new study, our ancestors between 2 and 3 million years ago started to spend far less time and effort chewing by adding meat to their diet and by using stone tools to process their food. The researchers estimate that such a diet would have saved early humans as many as 2.5 million chews per year, and made possible further changes that helped make us human."