The human species has been changing for millions of years. From the specimen commonly know as Lucy , it is possible that two species evolved: Australopithecus boisei, and Australopithecus africanus. These two forms are more commonly know as robust and gracile australopithecines. A sagital crest appears in the robust, and the mastoid process begins to develop a little. The supraorbital brow ridge is still prominent. In the robust species face, the palatal length decreases from 7.1 cm to 6.4 cm. The nasal breadth decreases from 2.5 cm to 2.3 cm, and the nasal height increases from 2.7 cm to 3.0 cm. The canine diastema that appeared in Lucy disappears in the robust, as does the slight projection of the canine tooth. The molar chewing surface area increases in the robust from 244 square mm to 490 square mm. The Gracile does not develop a sagital crest. His frontal bone is not as horizontal as the other two species, and the mastoid process is even more developed than the robust and Lucy. The palatal length increases slightly from Lucy s 7.1 cm to 7.3 cm. The nasal breadth and height also decrease from 2.5 cm to 1.8 cm and 2.7 cm to 2.1 cm. The infraorbital area becomes more depressed in the gracile species. In the mouth, the dental arcade becomes more parabolic, and the gracile also looses the canine diastema and the projecting canine tooth. The gracile s molar chewing surface area, which is 288 square mm, does not become as large as the robust. From the Australopithecine specimens evolves Homo Habilis. Evidence from specimens KNM- ER1813 and OH24 several changes occur. The face remains without a sagital crest and only in the OH24 is the mastoid process developed. The palatal length decreases to 5.7 cm in the KNM specimen, and 6.2 cm in the OH specimen. The nasal breadth for the KNM is 2.2 cm and 2.5 cm in the OH. The nasal height increases to 3.2 cm in the KNM and to 2.6 cm in the OH. The parabolic dental arcade for both habilis specimens follows suit with the gracile. The incisors become more procumbent in the habilis species as well. The molar chewing surface area ranges from 420 square mm in the KNM species to 340 square mm in the OH.
Homo habilis then gives rise to the species homo erectus. In the homo erectus braincase, the frontal bone becomes more vertical, and the mastoid process is well developed. In the face the palatal length increases to 6.3 cm, the nasal breadth increases to 2.9 cm, and the nasal height increases to 3.1 cm. The incisors become more vertical than in the previous habilis species. The teeth remain about at the average of the two habilis specimens. The molar chewing surface area is about 380 square mm.From homo erectus comes the Neanderthal species, the earliest of which is the Steinheim specimen. Little change occurs here. The infraorbital area becomes more depressed than in previous species, and the molar chewing surface area decreases to about 320 square mm. In the later Neanderthal species, such as the La Chapelle and the La Ferrassie specimens, the nasal measurements increase. The palatal length increases to 7.1 cm(la Chapelle) and 7.0 cm(la Ferrassie). The nasal breadth increases to 3.3 cm in the Chapelle and 2.8 cm in the Ferrassie. The nasal height increases to 3.4 cm and 3.6 cm respectively. The mcsa increases to 352 square mm in the Chapelle and to 385 square mm in the Ferrassie.The Neanderthal then gave way to the predmost or the early Homo sapien. The frontal bone of the braincase is much more vertical than in the Neanderthal species. The face measurements also decrease to a 5.7 cm palatal length, 2.4 cm nasal breadth, and a 2.3 cm nasal height. The infraorbital area is now depressed in the predmost. The dentition also decreases in size. The mcsa is now only 341 square mm. In the modern human much less has changed. The dentition has become even smaller with an incisor width of 2.4 cm, a molar length(left 3) of 2.4 cm, and a molar width of .9 cm. This calculates to a mcsa of 216 square millimeters. Modern human has experienced many changes in his evolution.