Human beings are believed to have evolved from apes, nonhuman and human like forms. Genetically human beings are linked to have evolved from the great ape. The earliest fossils that are considered to be the remains of human beings are the genus of australopithecines which are dated 4 million years ago and from australopithecines now came the genus homo. Genus homo evolved from australopithecine ancestors. Creationists have argued that australopithecines belong to the genus homo because of the similarities they share with them. There are four ways in determining whether a fossil is of that of an australopithecine and not of a great ape or genus homo. They can be differentiated by locomotion, the teeth, face and jaws, the brain size and lastly function.
In terms of face, teeth and jaws, australopithecines have post canine dentition which is moderately large (Leakey 94). Their front teeth have broad slanting incisors with projecting canines and have large back teeth. Their jaws are heavy with great chewing muscles and bony attachments. Australopithecus have large eye sockets compared to the genus homo that have small eye sockets. Australopithecines have lower faces which are protruding and also have a large bony orbit with protruding muzzles. In contrast, genus homo has short canines and vertically implanted incisors and small back teeth. They have less powerful muscles and do not have bony protrusions in the face but their faces are essentially flat. The genus homo has a flat face with no prognathism and gracile orbits. The difference between the genus homo and Australopithecus can also be seen in the head where the australopithecines have bigger heads and faces compared to genus homo which has smaller faces, teeth and jaws. Australopithecines have a large post canine dentition with enamel which makes them feed on hard objects comparably, genus homo do not have enamel post canine teeth (Nickels 4).
With regard to locomotion, Australopithecines have a higher brachial anatomy of longer arms than genus homo. Australopithecines have a higher brachial index of longer arms than legs which help them in swinging and hanging on trees. Moreover, they have naturally curved fingers and big toes which assist them to grasp branches while moving from one tree to the other while genus homo do not have curved fingers. Even though they are bipedal, they have a knuckle walking style of semi erectness. They are bipedal thus walked on two feet at the same time swung on trees comparably genus homo are bipedal but do not swing on trees. They have an opposable big toe while genus homo have non-opposable big toes and have strong supportive fully extendable knee joint to support the entire body while standing up (Toth and Kathy 60). In contrast, genus homos are bipedal and fully erect with longer legs and shorter arms, the longer legs help to support the body in movement. Australopithecines have got anatomical characteristics of the pelvic femur and spinal column which facilitates its bipedal locomotion
The brain size of australopithecines is smaller than those of genus homo. The main difference between the two is the cranial capacity, australopithecines have a cranial capacity of between 350cc-600cc which is smaller that that of the genus homo. Australopithecines have sagittal crest which is the ridge along the top of the skull while the genus homo lack the sagittal crest and have a thinner and smaller face. The Australopithecus had rough, thick and hard skin compared to genus homo which evolved to delicate skin and skeleton.
Leakey, Richard. The Origins of Human Kind. New York: Basic Books, 1994. Print.
Toth, Nicholas and Schick, Kathy. African Origin in the Human Past: World Prehistory and the Development of Human Societies. London: Thames and Hudson, 2005. Print.
Nickels, Mark K. Creationists and the Australopithecines. Journal of Anatomy, 6:3 (1986): 1-5. Print.