The human jaw and teeth have diminished in size from the time of our early pre-human, ape-like ancestors. Their protruding jaw may not be beautiful to us, but their teeth were better spaced and more orderly than ours. We have tinier teeth, but they are still packed tightly into small jaws, often crookedly. Unlike other mammals, our third molars, nicknamed "wisdom teeth," sometimes do not have room to erupt at all.

George Washington University anthropologist Peter Lucas says the modern mouth is in disarray.

"The norm is a mess! It's basically twisted, not in the right position, such that orthodontists are commonly needed in order to straighten it out," he said. "There isn't enough space. And thirdly, it's diseased. If the dentition is disordered such that the mouth can't clear particles properly, then it's got more of a chance to get gum and periodontal disease that typifies modern humans."

Mr. Lucas blames the situation on the invention of cooking and other methods to process food, like cutting and chopping. This may make meals much more palatable and easier to chew than the raw, hard fare our primate cousins like chimpanzees and gorillas eat in the wild. But the anthropologist told a recent science convention in Washington that it has taken its toll on the human jaw.

"Food preparation techniques that generally reduce the particle size that we take into our mouth have acted very rapidly to reduce front tooth size and the jaw size of humans," he said. "There has also been reduction due to cooking in our back tooth size due to reduction generally in the toughness of foods. But they are of synchronization. Front teeth, jaw size [are] reducing very much faster than the back teeth, so that leads to crowding in the mouth."

Nevertheless, we are not likely to give up cooking and adopt gorilla diets to try to reverse the situation. For one thing, that would be too hard on our teeth. Mr. Lucas says a raw potato is almost twice as stressful on our molars than a cooked one.

A George Washington University anthropology colleague not involved in this study, Bernard Wood, agrees that we have developed to eat soft foods. He also notes, however, that at least we survived, whereas our more hardy-toothed, jut-jawed ancestors became extinct. Dentists worldwide should be delighted at this turn of evolution.

"The things that allow us to thrive with our small teeth are the things that are leading our teeth to be disorganized and deranged and so on," said Mr. Wood. "We obviously have evolved in fits and starts towards having very small teeth. Unless now we have the ability to cook food or prepare it in some way, we would be completely finished. We have such a lousy, small dentition that we just couldn't cope."

Another scientist interested in teeth, Peter Ungar of the University of Arkansas, is studying fossil dental evidence to understand the evolution of the human diet. To get at this, he is examining the wear patterns of ancient teeth.

"Tooth shape tells you what an animal has evolved to consume, but tooth wear tells you what an animal actually ate," he said.

Mr. Ungar described for the science convention two new techniques to analyze shape and wear patterns on teeth to help infer diets. One method uses laser beam scanning to generate three-dimensional computer maps.

Enlarged, they look like the surface of the Earth.

"The cusps become mountains," said Mr. Ungar. "The fissures become valleys."

The other technique uses a microscope to determine surface abrasions of old teeth. The type of abrasion is a clue to what was eaten.

Animals that eat leaves and things of that nature, tough foods, tend to have scratches on the surfaces of their teeth," Mr. Ungar said. "As the teeth shear and slide past one another, the abrasives in between them get dragged along, forming scratches. Those primates that eat hard, brittle foods tend to have a lot of pits on their teeth because as the teeth come together in crushing and grinding, that forms pits."

Combining laser dental topography with microscopic abrasion patterns, Mr. Ungar hopes to differentiate among the diets of our various primate and early human predecessors.