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An Evolving Dentition: Human Teeth from an Evolutionary Perspective
Review by Jeffrey P. Bigham
The dentition of modern humans has experienced considerable evolutionary change, some up to the present day. The general trend in these changes is for both the jaw and dentition to have become smaller. In fact, studies have shown that from about 35,000 years ago until 10,000 years ago, tooth size has decreased on average by about one percent every 2000 years. From then until the present the rate has doubled to a one percent decrease every 1000 years (Recent Human Dentition Evolution). Various evolutionary, environmental, and cultural factors are responsible for this change.
Considerable evidence exists that shows that the importance of large teeth and jaws was reduced as humans developed over the last 50,000 years. While this reduction in importance alone may not explain why the human dentition actually reduced in size, it does make it more likely that the dentition would reduce if doing so would help relieve other evolutionary pressures, which will be explained later. The main causes for a decrease in evolutionary pressure to maintain a large dentition appear to be changes in the human diet, food preparation, and technology. These factors are mostly governed by behaviors unique to human beings and their development often caused an abrupt change in the way the human dentition had been evolving.
In general, the modern human diet contains more meat than that of our early ancestors. This means that over the course of time the teeth were required to process less course vegetable material, reducing the need for a large, herbivorous dentition. With the development of stone tools humans were basically able eliminate the need for many carnivorous adaptations by substituting their tools for the sharp teeth, large canines and strong jaws typical of carnivores. When humans began cooking their food in large earth ovens (perhaps as early as 200,000 years ago), this made the meat and other foods more tender and easier to chew, again reducing the need for a large, robust dentition.
|Another major technological innovation that affected the size of the human dentition was the development of pottery. Pottery allowed soups and other very soft foods to be made that required no teeth at all to consume. Around the time of the development of pottery, the remains of people that had lost their dentition and still lived on were found. This suggests that the importance of a full set of teeth had gone down dramatically. The widespread use of pottery marked acceleration in the amount of food preparation and processing that occurred in the form of stone ground grains and the precursors to modern milling. Because these developments led to food being softer and easier to chew it was accompanied by a decrease in the selective advantage of the possession of a large dentition. The selective disadvantage of losing the use of the dentition has all but disappeared in modern times due to the widespread availability of dental appliances, such as dentures, and highly processed foods. This is just one example of how the unique human ability to make technological advances has altered the course of change in the dentition.|
The previously mentioned factors all combined to ease the pressure on the human dentition to remain its previous, larger size, but this was most likely not the actual reason that became smaller. One theory is that unnecessary biological structures tend to shrink or even disappear completely if they are not being used. This could potentially be selected for because additional biological structures can consume additional resources and, therefore, eliminating them would presumably be to some advantage. While it is possible that such a mechanism was at least partially responsible for the reduction in size of the human dentition, several other evolutionary pressures most likely played a larger role.
First, evolution has tended to encephalize the brain as time has passed, and a larger brain requires a larger braincase to hold it. One of the most efficient means of creating such a larger braincase is to shorten the jaw considering that the usefulness of a large jaw and large dentition at this point is not as advantageous as it once was. Similarly, the development of bipedal locomotion created a subtle anatomical shift and an alteration of the braincase that also functioned to reduce the size of the jaw. As larger brains became the standard because of their apparent evolutionary selection advantage, the jaw became shorter to accommodate its expanded braincase. This caused some problems and is the basis for some of the most recent evolutionary changes in the human dentition.
Because the jaw has shortened so dramatically, the back molars are often crowded in the jaw, with the result being impacted or misaligned teeth if this problem is not remedied through the use of modern dental technology. Because such impaction of the “wisdom teeth” often led to infection, pain, and other dental problems in the past, it is most likely an evolutionary disadvantage for those who possess this trait. At some point in time, a random mutation resulted in this characteristic being suppressed in a portion of the population. This genetic trait had begun to gradually spread, but because of the advent of orthodontia and the tendency to remove the wisdom teeth before they become a problem, this trend is likely to stop. This is another example of how the intelligence that is unique to humans has halted the change in our dentition.
The evolution of several behaviors unique to humans resulted in a change of the jaw and dentition. One of the most important of these is the development of language, which requires dramatically altered and flexible oral structures. The evolution of speech was associated with changes in the base of the braincase and the pharynx, both of which indirectly affect the jaw and dentition.
Humans are unique in their ability to correct and compensate for the flaws in their dental systems by means of their own intelligence. This ability has shaped the human dentition from the beginning and with the advent of increasingly advanced dental technology this trend will likely continue into the foreseeable future.
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