The Green Man is an accepting sort of person. He has been friends with all sorts of people even some vegetarians. At least one of the said vegetarians has indicated in conversation that they viewed vegetarians as being deeper thinkers than your average omnivore. It will come as a big disappointment to these individuals then to discover that their capacity for such deep thought is being linked to their ancestors meat eating ways.

New research by Nancy Minugh-Purvis of the University of Pennsylvania in Philadelphia indicates that, lacking the constraints of a bulky chewing apparatus, the human skull may have been free to grow, enabling the massive development of the brain. The reduction in the need for a big jaw arose from a mutation 2.4 million years ago that left us unable to produce one of the main proteins in primate jaw muscles and marked a shift to a higher protein based diet.

Nancy summerises it nicely:

Humans may not have needed particularly strong jaws anyway. By then, our ancestors may have switched from eating chewy leaves all day long to snacking on smaller portions of meat.

Read more in Nature.