What’s missing in this picture is any reference to the pioneering work of Weston A. Price on the relation between diet and jaw formation. Here’s the story, from Clare Pain, at ABC Science in Australia:
“Lifestyle is known to affect many aspects of health but now a UK anthropologist says it could even change the shape of our jaws.
She made detailed measurements of the skulls and jaw-bones (mandibles) of nearly 300 individuals from 11 different subsistence cultures – some from hunter-gatherer societies and some from societies with primitive agriculture.
The measurements were of skulls in museum collections, which were from people who lived in the past couple of thousand years.
“These people are likely to be analogous to people living today,” says Cramon-Taubadel.
She found that people from hunter-gatherer societies had narrow, long mandibles, whilst people living an agricultural life tended to have short, broad jaw-bones.
Cramon-Taubadel then looked for correlations between the shape of their jaw-bones with other factors such as climate, geography, genetic make-up and type of lifestyle and found the difference was not genetic.
“The pattern was consistent, regardless of which part of the world the people came from,” says Cramon-Taubadel. “The results indicate that there is something biomechanical, rather than something genetic, that is altering the way the mandible grows.”
“Presumably the children growing up in these different situations have different chewing behaviour,” she says. Rather than happening over an evolutionary time-scale, the change to the mandible that she is talking about happens on an individual level as each child is growing up.
Cramon-Taubadel makes some suggestions for how chewing might differ between the two types of lifestyle. She thinks hunter-gatherers may chew more than people eating farmed food. “Agricultural populations tend to have a starch-based diet,” she says, “which may be softer”.
She also points out that hunter-gatherers probably chew for more of the day as they tend to browse rather than eating at definite meal times. Their diet may also include nuts and other tough foods.
There is some evidence from another species that jaw-bone shape may change with diet. Some rabbit-like animals called hyraxes have been shown to have about 10% less growth in their mandibles when they are fed soft processed food.
However, Cramon-Taubadel cautions that more research is needed to identify the actual reasons for the difference. For a start, the term ‘hunter-gatherer’ includes a wide range of diets. “Hunter-gatherers encapsulate Inuits, Australian Aborigines and forest people from the Congo,” she says, “and they are all doing very different things”…”