Haydee Munoz

01063896

ANT2033

15- April-2010

Physioanatomical Analysis of Australopithecus Afarensis

The first Australopithecus afarensis was found in 1974 by Don Johanson at Hadar in Ethiopia, Africa, and dates from about 3.9 to 3 million years ago. The very complete fossil is thought to be a female skeleton and it is called “Lucy” after a Beatles song. Because the skeleton is 40 percent complete, it facilitates a more accurate analysis in a broader sense. When comparing A. afarensis to a chimpanzee, a species with many traits that for hominins are considered primitive, and a modern human, it is concluded that the subject is very primitive, because it shows few developed traits.

The Lucy skeleton is female and it is approximately 3 or 4 feet tall, while other A. afarensis male fossils have been found that are about 5 feet tall. While male chimpanzees average height is 4 feet tall and female average height is 3 feet tall, the male human height average is 5 feet 9 inches and the female average is 5 feet 3 inches. Therefore, like chimpanzees, Australopithecus afarensis has smaller body size than the modern human. Also, A. afarensis is sexually dimorphic, which is a trait that is common for attraction and reproduction among apes, while humans are not very different in body size among sexes.

One of the most characteristic derived traits of modern humans is brain size. Modern humans have between 1150 to 1750 cm3, chimpanzees have 285 to 500 cm3, and A. afarensis have a 438 cm3 of cranial capacity. When these quantities are considered in comparison to body size, it is inferred that A. afarensis’ cranial capacity is bigger than chimpanzees’ cranial capacity since they are similar in height. However, even though a human is taller than an A. afarensis the ratio of brain and body size is not the same. Therefore, the brain of an A. afarensis is slightly bigger than that of a chimpanzee but much smaller than a human brain.

Many important derived traits are seen in the construction of a human skull. First of all, the foramen magnum is located more to the center of the bottom of the skull, because of the humans’ more developed bipedalism. On the contrary, chimpanzees’ and A. afarensis’ foramen magnum is closer to the back edge of the bottom of the skull, which indicates less developed bipedalism. Another derived trait is that the human skull’s broader part is in the upper part of the skull and it is very rounded, while chimpanzees’ and A. afarensis skulls are broader in the bottom part of the skull and have a backward horizontally elongated skull, which suggests thicker muscles on the neck to hold a less centered head caused by a less developed bipedalism. One more human characteristic is a larger forehead and small brow ridges, but chimpanzees and A. afarensis have no foreheads and even though chimpanzees have thicker brow ridges, A. afarensis’ brow ridges are very thick also. Also, humans have a very flat postorbital constriction and even though A. afarensis has a flatter constriction than chimpanzees, their mandibles are still very far out. In addition, humans use tools and have a smoother diet, so they have a small zygomatic because they don’t need thick muscles for their mandibles. On the contrary, chimpanzees and A. afarensis have bigger zygomatics than humans because of their diet. Also, chimpanzees and A. afarensis have a bigger ascending ramus of mandible than humans.

The diet an organism follows influences its anatomy. Even though humans, the A. afarensis, and the chimpanzees share the same dental formula (2-1-2-3), their teeth are very different. A. afarensis molars are bigger and thicker than chimpanzees and humans, while humans have smaller teeth than the other two species. Also, both chimpanzees and A. afarensis have a larger and pointed canine. In conclusion, A. afarensis and chimpanzees have sharper and bigger teeth than humans, because their diet is tougher.

The main characteristic of hominins is their ability to walk on two feet. However, this was a long process of evolutionary change throughout a long period of time, so many earlier hominins had a less efficient posture and structure than more modern hominins. The human pelvis is narrow, short, circular, and is constructed in a basin shape while all of the pelvis’ bones are well balanced for a standing position. In contrast, the chimpanzee has a long, narrow, and flat pelvis, which is very unstable for bipedalism. Moreover, the A. afarensis has a somewhat circular pelvis, more narrow but bigger in anterior-posterior breadth. A. afarensis Pelvis is much more like humans than chimpanzees.

Another important sign of evolved bipedalism is the shape and size of the extremities. Human femurs are longer than the tibia but not much; also, they are attached closer together on the pelvis to increase stability. Human upper extremities are shorter than lower extremities, our fingers and toes are shorter, and our feet are arched to walk better. Also, the human vertebral column has convex and concave arcs to help support the weight, and it is placed vertically on the pelvis. In the case of chimpanzees, their femur is a lot longer than the tibia, and their femurs are not shaped to fall under the pelvis as human femurs; instead they are attached to the sides of the pelvis. Also, their upper extremities are extremely long as well as their fingers and toes and their feet are not arched, because they are not structured to walk in two feet even if they can because they spend a lot of time climbing trees. In addition, their vertebral columns are convex, and even though they can stand up in two feet, their columns are not vertically attached to the pelvis. In the case of A. afarensis, their femurs where shaped as human femurs, so they could walk in two feet. Also, their upper extremities are longer than humans but much shorter than chimpanzees, which can be proof that they still climbed trees sometimes. Because A. afarensis fingers and toes were long and their feet were arched, there is a possibility of a bipedal species with climbing abilities. Also, their vertebral column was vertically attached to the pelvis and probably shaped somewhat like the human column. Therefore, A. afarensis is an hominin because its bones where structured to walk on two feet, but it still showed primitive traits of climbing bone structure.

A human is characterized by its complex behavior and culture. An important part of culture is the objects humans make that show what is important to them. However, not only humans use tools chimpanzees also use very rudimentary tools. Anyway, whether chimpanzees have a culture or not is still under discussion. A. afarensis was thought to be of a so early period of time that no tools were fabricated. However, A. afarensis has a thick thumb as the human does, which has led to believe that they were tool builders also. In comparison, chimpanzees do not have a thick thumb due to the fact that they don’t use tools that often neither fabricate complicated tools. Therefore, A. afarensis was a toolmaker just as humans are.

Lucy has many features that suggest the lifestyle she used to have. She was female because of her small stature and the shape of her pelvis. Also, she used to live in an arboreal ecosystem because she still needed to climb trees. In addition, she had a tougher diet than humans and because the tools she made were not as elaborate, her dentition is much thicker. She was bipedal because she had all the main characteristics needed for bipedalism; even though, she might not have walked as erect as humans. Because she could walk, she probably migrated constantly to places where the living conditions were better.

A. afarensis is one of the many points in the line of human evolution. She was more like humans because she was bipedal and she used tools. However, she shows several primitive traits that link her close with chimpanzees. Lucy had climbing structured upper extremities, small brain, sharper and thicker teeth, stronger head muscles, and sexual dimorphism. Because brain size is related with complexity of behavior, it is likely that Lucy had not the complexity level of culture we have nowadays. Therefore, A. afarensis, when compared to humans and chimpanzees, has more common traits with chimpanzees although it shares the most important traits of hominins with humans.

Bibliography

Ferguson, Walter. Australopithecus Afarensis: A Composite Species. Primates v.33 no.2. 1992. Pp. 273-279

Johanson, Donald C. Lucy, Thirty Years Later:An Expanded View of Australopithecus Afarensis. Journal of Anthropological Research. V.60 no. 4. 2004. Pp. 465-486

Jurmain, Robert, Lyyn Kilgore, Wenda Trevathan, Rusell L. Ciochon. Introduction to Physical Anthropology. 2009-2010. Wadsworth Cengage Learning.

Hartwig-Schrerer, Sigrid. Was “Lucy” More Human Than Her “Child”?: Observations On Early Postcranial Skeletons. Journal of Human Evolution. V.21 no.6. 1991. Pp. 439-449

Wilford, John Noble. New Analysis of Fossils May Muddy Accepted Path of Human Evolution. July 1998. http://www.nytimes.com/1998/07/28/science/new-analysis-of-fossils-may-muddy-accepted-path-of-human-evolution.html?scp=18&sq=australopithecus%20afarensis&st=cse

Wilford, John Noble. Toolmaker’s Thumb Not Unique to Humans. September 1994. http://www.nytimes.com/1994/09/13/science/toolmaker-s-thumb-not-unique-to-humans.html?scp=20&sq=australopithecus%20afarensis&st=cse&pagewanted=1