By Michelle Roberts
BBC News health reporter, Washington DC
The way our diet has evolved over time could explain why many children need braces to get the perfect smile, according to US paleoanthropologists.
Teeth have adapted to mushy food
Early Man learning to cook food and cut it up with tools has led to our teeth and jaws shrinking over time, they say.
Fossil evidence shows we have evolved to eat mush, the scientists say.
But as jaws have become smaller, they have had to accommodate the same number of teeth, often leading to the teeth becoming crooked, they add.
If for any reason we are forced back into eating tough, raw foods we could be in trouble, they suggest.
Dr Bernard Wood, of George Washington University, said: "We're a pretty puny bunch, really, with small teeth and small jaws.
"If we can't get the foods we like, and we have to adapt quickly, we might be in a terrible mess because our teeth and jaws aren't equipped to cope with anything very substantial."
Wear and tear
Professor Peter Ungar, from the University of Arkansas, has been looking at smart new technology that should help those studying fossils of human teeth.
The instrument uses high-resolution laser scanning combined with geographic information systems.
This gives three-dimensional information about wear and tear on teeth.
"We can infer the diets of fossil primates by comparing the length and shearing of crests on unworn molars with those of living species with known diets," Prof Ungar said.
"Living primates that eat leaves or insects, for example, have longer crests for shearing and slicing these tough foods.
"In contrast, those that consume nuts and seeds have blunter molar teeth with shorter crests for crushing and grinding these hard, brittle foods," he said.
Peter Lucas, also from the George Washington University, said the first human ancestor probably learned to cook to spare his teeth.
After all, cooked potato can reduce stress to molars by up to 82%, compared with raw potato, he said.