Question

Construct a research on the evolution of teeth and Jaws

1500 words essay format

the history of the evolution of the topic

include hypothesis

a controversy regarding the topic.

Answer 1

The evolution of teeth and Jaws

The jaws and teeth of Homo sapiens have been evolved, from the last common ancestor of chimpanzee (Pan troglodytes) and men to their current form. These changes were driven by the types and processing of food eaten. The evolution of the jaw is thought to have facilitated encephalization speech, and the formation of the uniquely human chin. The evolution of the masticatory complex is related to other anatomical features such as brain size and bipedal posture, and leads to important proceedings like the formation of speech and language.

Human masticatory, system, which consists of maxilla, mandible, teeth, temporomandibular joint, and the masticatory muscles, is functionally involved in not only feeding, but also speech. It is now believed that there was more than one evolutionary lineage within the human clade.

Dental and orofacial features of the extinct hominin taxa

The teeth and jaws of humans are smaller than great apes . Investigations on fossils have also shown the evidence of a decrease in the size of the masticatory system in the hominins which are accepted to be the ancestors of Homo sapiens. Researchers have stated that this decrease was mostly due to the changes in the eating habits of the species.

There are morphological differences that separate the modern humans from living apes, these include the characteristic of the dentition, skull, brain, trunk and the teeth. For example, canine teeth of the apes are sexually dimorphic when compared to the humans and they usually are not worn down to the level of the occlusal surfaces of the posterior teeth. Human jaws are also smaller, more gracile, and project less than those of equivalent sized living apes. These features, that differentiate the modern humans from living apes, could also be found between modern humans and early hominins, together with similarities between the taxa.

Last common ancestor of chimpanzees/ bonobos and hominins had large incisors and were procumbent when first erupted. The canines were sexually dimorphic, males had more projected canines than the females. Premolars had relatively small crowns and the second molar was the largest of the molar teeth just like in all of the great apes. Also similar to most monkeys and great apes, the upper canines posterior edge was sharpened against the anterior extension of the anterior lower premolar in Ardipithecus.

Incisors were certainly procumbent at the time of eruption in the earliest and archaic hominins . However, the incisor teeth were relatively small and more vertical in the archaic megadont hominins and the genus Homo. This reduction in the incisal size was combined with the enlargement of the premolars and molars.

Canine teeth are believed to be small in the earliest hominins and this reduction in size continues during the early period . Megadont archaic hominins present the greatest size reduction of the canines and the premolars are abnormally large in these taxa as reported by Wood and Stack . Hominin males generally have small canines, it is stated that, the higher the jaw joint, the smaller the canines are in males and generally, temporomandibular joint is high in the hominoids.

In the modern humans, the first molar teeth are the largest among the molars and the overall tooth size is reduced. In the earliest hominins and archaic hominins, second molars were generally the largest of the molar teeth and the third molars were closer in size to the second molar. Lucas et al stated that food particles are not certain to be broken totally by the teeth, for the tooth surfaces form only a small amount of the oral surface and this is why the cheek muscles and the tongue have a great importance in chewing and keeping the food particles between the teeth. It is generally believed that the early hominins and archaic megadonts were small object feeders. Second premolars contribute more to the tooth row when the first molar/ third molar ratio is high and this is correlated to the canine tooth size. This might be due to the larger premolars extending the cheeks anteriorly reducing the size of the mouth slith.

Distinctive maxillofacial anatomical features of Homo sapiens

The protruding chin is one of the evolutionary features which separate Homo sapiens from our ancestors. A protruding chin was absent in archaic humans and Neanderthals. Masticatory system related biomechanical forces were believed to play a role on the formation of the human chin. The occlusal plane in humans is often not horizontal. A helicoidal occlusal plane is an inclination of the teeth where the anterior cheek teeth show a plane sloping upward palatally while the more posterior teeth have a plane sloping upward buccally forming a twisted occlusal plane. Even though the helicoidal occlusal pattern has been regarded as a feature typical for the orofacial region of Homo, it is also seen in the plio- Pleistocene hominids and in non-human primates, especially the chimpanzees.

The posterior teeth of the humans are also inclined in the sagittal plane. Human lower third molars have undergone a forward tilt during the course of evolution as a result of the displacement of the temporomandibular joint in relation to the oclusal plane. This developed the curve of spee which is more pronounced in humans when compared to the other hominids. This also rendered the third molars functional despite their disadvantageous position.

When the evolution of the mandibular condyle is evaluated, it was shown that the early hominins inherited a low and anteriorly placed joint from some ramamorph ancestor with a similarly placed joint point. In the ausralopitecine line, the joint remained forward but was raised. In the Homo erectus group it was raised less and displaced backward. Neanderthals had a high ramus width, but they had widely different values of ramus height.

Diet and dental evolution

Analyses of the tooth shape, tooth size, enamel shape and dental micro wear together with dental biomechanics, suggest that there have been a shift in the dietary capacities of the australopithecines which has helped them survive in climatic variability. Studies on the teeth of Australopithecus anamensis, Australopithecus afarensis and Australopithecus africanus suggest that hard and abrasive foods had gained importance through the Pliocene period.

Australopithecines also had large and flat molars. It is mostly believed that these Miocene period apes fed on folivory, soft fruits and hard objects. Australopithecines, which had large and flat molar teeth, were suitable for hard and brittle foods like some fruits nuts flowers and buds. Studies also show that the australopithecines have acquired the ability to eat hard objects through time.

The transition from foraging to food providing economies involved profound changes in immobility, social organization and technology. It is hypothesized that, with the use of tools for cutting and grinding, the need for carnivore adaptative characteristics such as strong jaw bones, large canines and stronger masticatory muscles started to decrease.

It has been hypothesized that the invention of pottery and changes in food production following the use of pottery, relaxed the selective forces on the masticatory system and the onset of probable mutation effect resulted in a consequent reduction in tooth size.

Cooking is another factor on lessening the need for carnivore adaptations.It has been reported by various authors that a decrease in the dental dimensions started to appear with the use of controlled fire for cooking , It is also stated that the control of fire and the use of language are strongly related, for the teaching the next generation how to use fire needs the use of language . It is known that australopithecines had the use of flake tools. Experiments have shown that the cut marks on the long bones from the Pliocene- Pleistocene period were not made by carnivore teeth but by tools.

Speech and the Upper Airway

Evolution of human masticatory system is not only related to diet and food processing techniques, but also brain size, bipedalism and speech (language).

Speech and language need a flexible oral system. This flexibility is maintained by providing processed and softened food, which does not require a strong musculoskeletal build and sharp teeth. The language enabled humans to coordinate their actions for providing food and increase the foraging ability of our species. Hiimae has stated that human oropharyngeal system differed from other mammals for having communication as a dominant function.

It has been hypothesized previously that, a larger cranial vault for a larger brain is maintained by the decrease in the size of the mouth. It has also been stated that bipedal posture required a smaller mouth for the arrangement of the center of gravity of human cranium.