The badlands of the Afar Triangle, Middle Awash area near Hadar, Ethiopia in northeast Africa are a rich resource for finding early hominid fossils such as Dr. Donald Johanson and his team discovered over the course of several seasons in the mid-1970s. During the Pliocene Epoch (between 5 and 2 MaBP), this area was dominated by lakes (Zihlman 2000) and woodlands. It is along the edge of these now-dried lakes among the former woodlands that fossils can be located (Shreeve 1996).
After death, several things can happen to the body. From the perspective of the physical anthropologist, the best thing that can happen is that the body lies in an area where it will be covered quickly by sediment. Such must have been the case with the 40-percent-complete skeleton found by Dr. Johanson. Known informally as Lucy and formally as AL-288-1 (Afar Locality #288), she was found in a sedimentary layer that eventually was dated at 3.5 MaBP (Johanson, Edey 1980).
Skeleton likeness courtesy of boneclones.com |
Johanson, along with colleague Tom Gray, had been mapping another locality at the Afar site. Feeling "lucky," Johanson took a short detour into another area later mapped as locality 288 and "noticed something lying on the ground partway up the slope" (Johanson, Edey 1980). This "something" turned out to be the exposed portion of a hominid arm bone.
Shortly, Johanson and Gray had excavated several bones and soon realized that they were probably looking at the bones of just one individual, rather than the scattered bones of several individuals. After retrieving several pieces of jaw, they returned to their campsite to note their discovery and let the others know what they found. |
That afternoon, Johanson and his team sectioned off the site to prepare for the collecting of the remaining bones. After three weeks of work, they had collected several hundred pieces of bone, which represented 40 percent of a single skeleton. The team knew these bones belonged to one single individual because there was no duplication of any one bone (Johanson, Edey 1980).
"Later in the night of November 30th [1974], there was much celebration and excitement over the discovery of what looked like a fairly complete hominid skeleton. There was drinking, dancing, and singing; the Beatles' song 'Lucy in the Sky With Diamonds' was playing over and over. At some point during that night no one remembers when or by whom the skeleton was given the name 'Lucy.' The name has stuck" (Johanson website).
Johanson, the son of Swedish immigrants, grew up in Hartford, CT. A neighbor was an anthropology teacher and Johanson took an interest in this field. The neighbor, however, tried to dissuade him stating that there is no money in anthropology. Johanson, the neighbor thought, would do much better for himself if he studied chemistry.
After enrolling in the University of Illinois chemistry department, Johanson became bored and found himself visiting the anthropology department more and more frequently. He eventually changed his major and spent several summers on archaeological digs in the Midwest. Then he transferred to the University of Chicago and studied under F. Clark Howell, known for his analyses of Homo erectus behavior.
Johanson completed his doctoral thesis on chimpanzee dentition and spent several seasons in the early 1970s exploring Ethiopia and was impressed with the potential of the Afar region (Johanson, Edey 1980).
After completing his PhD, he began teaching at Case Western Reserve University and continued his explorations of the Afar Triangle. By 1974, he was a curator at the Cleveland Museum of Natural History. Returning to the Afar region, he found Lucy and, in 1975, found an amazing array of bones of thirteen Australopithecus afarensis individuals, now known as The First Family (Johanson, Edey 1980).
Believing himself to be "lucky", Johanson states, "I am superstitious. Many of us [paleoanthropologists] are, because the work we do depends a great deal on luck. The fossils we study are extremely rare, and quite a few distinguished paleoanthropologists have gone a lifetime without finding a single one" (Johanson, Edey 1980). Although this was only his third year in Hadar, he had already found several fossils and the day of the Lucy discovery, he was feeling that special "lucky" feeling. Regardless of the heat that day (the early morning began in the 80s), he pressed on. By the time of discovery, the temperature was 110 degrees (Johanson, Edey 1980).
He worked closely with Tim White to classify the skeleton and, in 1978, agreed with White that Lucy was a new species and named her Australopithecus afarensis, rather than a species of Homo. Johanson later founded the Institute of Human Origins in Berkeley, CA, which he moved to Arizona State University at Tempe in 1997 (Johanson, Edey 1980).
Although Johanson does not provide field sketches of the Afar site, the following image serves to explain the basic geology under which Lucy, and later, "The First Family", were found. After millennia of sedimentation, the occasional albeit rare rains begin slowly to expose older layers of earth. Erosion of such sedimentation is probably the physical anthropologist's best friend in exposing bones or allowing for the exploration of sites that would appear otherwise unpromising.
Potassium decays to argon gas and can be dated, which is how the Lucy skeleton was dated at 3.2 MaBP. As the following image shows, volcanic ash dated at 3.2 MaBP lies just above the layer where the fossils were found. Beneath the layer of rock and dirt lies another layer of volcanic ash, dated at 3.8 MaBP. This stratification told the scientists that Lucy died somewhere between 3.2 and 3.8 million years ago.
Lucy lived at a time when the Afar region was not a desert environment. Rather, it was probably woodlands and savannah. Australopithicus afarensis, not totally ape and yet not quite human, probably lived in a variety of habitats, having evolved into being bipedal as an adaptation to living in the open areas. This hypothesis would make sense because by being bipedal in the open sunlight exposes less body surface to the sun, keeping them cooler in spite of a lack of shady areas (Tattersall 1996). However, fossils are being found in the formerly woodland areas and near water, not in the open areas, making the savannah hypothesis less plausible (Shreeve 1996). And Lucy's skeleton proves that her kind was bipedal by the shape of her pelvis and the angle the femur takes from the hip socket to the knee joint. From her waist down she was hominid, and from her waist up she was still ape, as her skull was still the size of a chimpanzee. The discovery of Lucy proves that bipedalism predates big brain size (Johanson et al 1982 (a), Shreeve 1996).
Lucy's skeleton, at 40 percent, is the most complete skeleton of any one individual of her age; remarkable in some ways, frustrating in others. Shell bemoans that there is no way to tell Lucy's gender because there is only one pelvic bone in existence and that one is hers, leaving no room for comparison (Shell 1991). Since the Australopithecus afarensis gave birth to offspring with ape sized brains there would have been no need for an enlarged birth canal. Johanson argues that, considering the vast collection of bones he has compared, the femoral bones show morphological identity and the size difference is attributed to sexual dimorphism (Johanson, White 1979). From bone measurements (figure 1), he was able to ascertain that Lucy probably stood three-hand-one-half feet tall and weighed sixty pounds (Johanson et al 1982-b). She was probably between twenty-five and thirty years old and showed some signs of possible arthritis (Johanson, Edey 1980). Johanson notes the "hyperstotic bone" with the worst being on vertebrae T6 and decreasing in severity through T-11 (Johanson et al 1982 b).
Gender is probably not the most important aspect to the Lucy fossil as she offers much more insight into our ancient lineage. Although no other pelvis from this species has been found, other Australopithecus afarensis bones have been and reveal much about sexual dimorphism to infer her being female. Regardless of the gender argument, Lucy's pelvis tells much more; it screams "bipedal." DeWaal points out that "the most significant difference between Lucy and modern chimpanzees is found in their hips, not their craniums" (DeWaal 1997).
It is Lucy's pelvic and femur structure, along with her knee joint, that are decidedly hominid. As Tattersall points out, short of having a pelvis to examine, the knee tells the most about locomotion (Tattersall 1996):
| "In a quadruped – an ape, say – the feet are held far apart, and each hind leg descends straight to the ground beneath the hip socket. In bipedal humans, on the other hand, the feet pass close to each other during walking so that the body's center of gravity can move ahead in a straight line. If this didn't happen, the center of gravity would have to swing with each stride in a wide arc around the supporting leg. This would be extremely clumsy and inefficient, wasting a lot of energy. So in bipeds, both femora angle in from the hip joint to converge at the knee; the tibiae then descend straight to the ground. In the human knee joint, this adaptation shows up in the angle – known as the "carrying angle" – that is formed between the long axis of the femur and tibia." |
The "carrying angle" can also be stated as "weight bearing axis" as shown below (Zihlman 2000). The chimpanzee, which is a quadruped, has a femur that comes straight out of the hip socket, while Lucy and the modern human exhibit the bipedal carrying angle.
Zihlman offers some basic measurements in the form of a comparative drawing, featuring Lucy, a chimpanzee and a human (Zihlman, Simmons 2000). In the following sketch, we can readily see the differences between the chimpanzee and the Australopithecus afarensis, especially with regard to the pelvic shape and tilt of the sacrum, which are decidedly hominid. Lucy's arms are also shorter than that of an ape, while still maintaining a longer ratio of arm length to overall height than that of a modern human. Furthermore, her arms are still longer than the overall length of her legs, although the ratio is not as high as in apes. From her skeleton, comparing it to chimps and humans, we can see that she is somewhere in between, on her way to becoming human (Zihlman, Simmons 2000).
Lucy's mandible also shows traits of both chimpanzees and modern humans as can be seen in the following image taken from Zihlman's coloring book. Apes' mandibles show parallel rows of molars as opposed to the wide U-shape of modern human. Lucy's dentition is a cross between ape and human in that the overall shape is apelike while the canine tooth size resembles that of modern humans.
In the chimp's mandible, we see a space between its incisors and large canine, which does not occur in Australopithecus Afarensis females. Furthermore, we see a reduction of incisor and canine tooth size more in line with that of a modern human while the molars are closer to the chimps' in size. The canine, however, is large and asymmetric and projects slightly beyond the tooth row (Johanson, White 1979). It is believed that Lucy feasted mostly on fruits and fibrous materials, climbing trees occasionally for food (Tattersall 1996). However, the enamel is thicker on the Australopithecus afarensis molar than on either the chimpanzee or human (Zihlman 2000).
The jaw also shows prognathism, a jutting forward of the lower facial features commonly found in the apes and other pre-human fossils although Lucy's jaw is not as pronounced as that of the ape.
Whether Lucy was completely terrestrial is a matter of debate. Some (Shreeve 1996, Tattersall 1996, Zihlman 2000) believe that she maintained some vestiges of her arboreal ancestry by climbing trees at night to seek shelter from predators during sleep periods, to eat fruits and leaves of trees and sometimes to scavenge a kill which is stored for "safekeeping" by predators (Tattersall 1996). There has been no evidence of tool making nor is there clear evidence of meat eating. It is plausible that Lucy and her kind used tools such as branches that would have decayed by now. This supposition is possible because chimpanzees make and use rudimentary tools for "fishing" for termites and leaves as sponges for drinking after a hard rain (Goodall 1986).
Johanson's discovery of Lucy is significant in our understanding of human evolution because she is the oldest, most complete erect-walking human ancestral skeleton found to date (Johanson, Edey 1980). In addition to having characteristics halfway between ape and hominid, she proves that bipedalism was prevalent long before enlarged brain size and dispels the belief that humans became bipedal to accommodate their capacity for tool making and the need to have their hands free for their tools and the kills they can make with those tools.
Lucy's skeleton was housed in a custom made box lined with yellow foam with cutouts for each bone. Johanson kept her in a safe for five years while he was with the Cleveland Museum. She has since been returned to Ethiopia and is housed at the National Museum of Ethiopia in Addis Ababa (Johanson website).
It is generally accepted that hominids diverged from the apes between 6 and 5 MaBP. Australopithecus afarensis led to 2 further divergences, the robust australopithecines that died out, and the gracile line leading eventually to us (Johanson, White 1979) figures a & b.
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Literature Cited
DeWaal, F. 1997. Are We in Anthropodenial? July 1997. Discovery Magazine.
Goodall, J. 1986. The Chimpanzees of Gombe: Patterns of Behavior. The Jane Goodall Institute.
http://www.janegoodall.ca/index.html accessed 11/23/02
Johanson D, Edey M. 1980. Lucy: The Beginnings of Human Kind. New York. Simon & Schuster.
Johanson D, White T. 1979. A Systematic Assessment of Early African Hominids. Science 202:321-330.
Johanson D, Taieb M, Coppens Y. 1982 (a). Pliocene Hominids From the Hadar Formation, Ethiopia (1973-1977): Stratigraphic, Chronologic, and Paleoenvironmental Contexts, With Notes on Hominid Morphology and Systematics. American Journal of Physical Anthropology. 57:373-402.
Johanson D, Lovejoy O, Kimbel W, White T, Ward S, Bush M, Latimer B, Coppens Y. 1982 (b). Morphology of the Pliocene Partial Hominid Skeleton (A.L. 288-1) From the Hadar Formation, Ehtiopia. American Journal of Physical Anthropology. 57:403-451.
Johanson D. Institute of Human Origins. Tempe, AZ.
http://www.asu.edu/clas/iho/lucy.html accessed 11/23/02.
Jurmain, Kilgore, Nelson, Trevathan. 2000. Introduction to Physical Anthropology. Belmont, CA. Wadsworth/Thomson Learning.
Shell, E. 1991. Flesh and Bone. December 1991. Discover Magazine.
Shreeve J. 1996. Sunset on the Savanna. July 1996. Discover Magazine.
Tattersall, Ian. 1996. The Fossil Trail: How We Know What We Think We Know About Human Evolution. New York. Oxford Press.
Zihlman A., Simmons C. 2000. Human Evolution Coloring Book. New York. Harper Collins Publishers.
Graphics Credits
Map. http://users.hol.gr/~dilos/prehis/prerm3.htm
Lucy skeleton. http://www.evolutionnyc.com
Stratigraphy drawing. Park M. 2000. Introducing Anthropology: An Integrated Approach. Mountain View, CA. Mayfield Publishing.
Distal Femora Comparison. Johanson D, White T. 1979. A Systematic Assessment of Early African Hominids. Science 202:321-330.
Pelvis comparative. Zihlman A, Simmons C. 2000. Human Evolution Coloring Book. New York. Harper Collins Publishers.
Chimp, Australopithecus afarensis, human comparative. Zihlman A., Simmons C. 2000. Human Evolution Coloring Book. New York. Harper Collins Publishers.
Dentition comparative. Zihlman A. ., Simmons C. 2000. Human Evolution Coloring Book. New York. Harper Collins Publishers.
Figures a & b. Johanson D, White T. 1979. A Systematic Assessment of Early African Hominids. Science 202:321-330.
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