Nature http://doi.org/bdfk (2016)

One quandary in human evolutionary research is how to explain the dramatic reduction in chewing tooth size and mandibular musculature seen in early species of the genus Homo compared with that of earlier australopithecines. Katherine Zink and Daniel Lieberman of the Department of Human Evolutionary Biology, Harvard, now propose that the change began when stone tools were used for slicing or pounding meat and root vegetables to improve their edibility.

Credit: © BLEND IMAGES/ALAMY STOCK PHOTO

Making food easier to eat lowers the required muscular effort and increases efficiency of mastication. It was previously suggested that fire was the first processing agent to make meat and tough, fibrous plants more easily consumable. However, other food preparation techniques would have been available before the advent of cookery.

Volunteers were asked to eat stringy goat meat and woody root vegetables including carrots, beetroots and jewel yams, to replicate foodstuffs available two million years ago on the African savannah. The researchers then compared the amount of chewing needed to eat unprocessed, pounded/sliced and cooked mouthfuls. 40,000 daily chews are needed to consume an unprocessed ‘vegetarian’ diet but pounding tough plant foods could reduce this by 5%, and by 17% when combined with meat processed in similar ways. Such a reduction in the extent and force of chewing may have facilitated the evolution of hominin teeth and jaws.