Wednesday, April 7, 2010

Lucy in the Sky with Diamonds

Creationists vary on how conservative they adhere to the seven (technically six) days of creation as described in the bible. Some creationists believe in microevolution but not macroevolution while Coyne states that "liberal creationists admit that some species could have evolved from others, (but) all creationists draw the line at humans" (193). What seems to be the major barrier in the debate of evolution versus intelligent design is how Homo sapiens came to be so incredibly different from other animals, both physically and mentally. It was a scientific milestone when Johanson discovered "Lucy", a Australopithecus afarensis, in 1974 (200). This nearly complete fossil lived 3.2 million years ago and helped close the gap between modern humans and the missing link between humans and chimpanzees. In which ways did the anatomy of Lucy help close this gap? Explain how Lucy specifically showed how human anatomy is physically traceable to other species. In what other humanoid fossil discoveries helped close the mental gap?


  1. In 1974, Donald Johanson found what I would consider the “missing link” between humans and chimpanzees because she is a mixture of various characteristics. As Coyne states on page 202, “from the neck up, she’s apelike; in the middle she’s a mixture; and from the waist down, she’s almost a modern human.” Therefore, she closed to gap between humans and chimpanzees.

    First of all, Lucy is a bipedal walking primate, meaning that she would have walked on two feet. This was made possible because her femurs angled in towards each other as opposed to a chimpanzee whose femurs are slightly turn outwards. The inward angle causes gravity to remain centered while moving which prevents the swaying motion chimpanzees exhibit when they walk on their two rear limbs (200). In 1976, Mary Leakey’s discovery of the Laetoli footprints reasserted that Lucy, Australopithecus afarensis, was walked on two feet. These tracks are identical to those of Lucy’s, and very similar to modern humans. They are strong proof the A. afarensis walked on two legs because there are not any depressions that would indicate knuckle-walking (201). The fact that Lucy walked on two feet is the most compelling evidence that Lucy is the missing link between humans and chimps. In addition, there are similarities between her skull and a modern humans. For example, she has a semi-parabolic tooth row and reduced canine teeth (202).

    Although Lucy’s brain is nowhere near the full development of a Homo sapiens’s, it is larger than a chimps. This is why it is still considered a why it is Australopithecus which has a smaller brain, instead of Homo which has a larger brain. Further down the evolutionary line, Lucy may evolved into Homo habilis. H. habilis has a larger brain and is considered the first species to use complex tools. In addition, one cast of H. habilis shows swelling of the brain in the areas that correspond to Broca’s area and Wernicke’s area in humans. These two areas are used for oral communication and comprehension and may be evidence that H. habilis was able to communicate through a spoken language.

    Why Evolution is True by Jerry Coyne

  2. AL 288-1, or more famously known as “Lucy”, was a major evolutionary find. When her newly excavated fragments were pieced together, she turned out to be a female of a new species, Australopithecus afarensis. According to scientists, she was the missing link between modern humans and chimpanzees. The reasoning for this is because of the way the femur connected to the pelvis at one end and to the knee at its other. In a bipedally walking primate like ourselves, the femur is angled in toward the middle, just like it was in Lucy, proving that she could walk on two legs instead of walking on all fours. (Coyne 200). The “Laetoli footprints” discovered by Mary Leakey and Andrew Hill in 1976 also prove that A.afarensis walked upright on two feet after examining the eighty-foot trail made by the two hominins (Coyne 201). Like Grace highlighted, Lucy closed the gap between humans and chimpanzees because she had features from both species. She had a very apelike head with a chimpsized braincase, but her human-like skull had a semiparabolic tooth row and reduced canine teeth (National Geographic). Also, her arms resembled a mixture of both species because they “were relatively longer than those of modern humans, but shorter than those of chimps, and the finger bones were somewhat curved, like those of apes” (Coyne 202). This clearly shows how human anatomy is physically traceable to other species because if there are similarities of bone structure among humans and another species, then it’s quite clear that those indicate that evolution must have taken place. Lucy is clearly an ancestor of modern humans because of the “upright posture and bi-pedalism preceded the development of what we would recognize as human beings and human intelligence” (Species Timeline).
    However, Lucy is not the only one that helped close the gay between the two species. One of the greatest leaps forward in human evolution was the ability to make and use tools. The first tool-using human was Homo habilis, and it appeared 2.5 million years ago, not too long after Lucy. Homo erectus was discovered 0.7 million years after that. It had a striking resemblance to humans with a brain about 74% of the size of a modern man. Its forehead was less sloping and the teeth smaller (Wikipedia). After that, Homo antecessor was discovered, and after that, Homo heidelbergensis, with a brain about 93% the size of Homo sapiens. These humanoid discoveries showed the progress of chimps towards humans, with increasing brain size and improvement in posture. Lucy was the last of the line of Hominidae and the line of Homo, just previously described, followed after and showed how it added to the structure of modern humans. (National Geographic) (Species Timeline)

  3. Lucy is the common name of AL 288-1, the nearly 40% complete skeleton of an Australopithecus afarensis specimen discovered in 1974 at Hadar in the Awash Valley of Ethiopia's Afar Depression. Lucy is estimated to have lived 3.2 million years ago. The discovery of this hominid was significant as the skeleton shows evidence of a small skull capacity akin to that of apes and of bipedal upright walks akin to that of humans, providing further evidence that bipedalism preceded increase in brain size in human evolution. In 1994, a new hominid, Ardi, was found, pushing back the earliest known hominid date to 4.4 million years ago, although details of this discovery were not published until October 2009. (Wiki)

    Lucy is significant in our understanding of human evolution because she is the oldest, most complete erect-walking human ancestral skeleton found to date. 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.

    One of the most striking characteristics possessed by Lucy was a valgus knee, which indicated that she normally moved by walking upright. Her femoral head was small and her femoral neck was short, both primitive characteristics. Her greater trochanter, however, was clearly derived, being short and human like rather than taller than the femoral head. The length ratio of her humerus to femur was 84.6% compared to 71.8% for modern humans and 97.8% for common chimpanzees, indicating that either the arms of A. afarensis were beginning to shorten, the legs were beginning to lengthen, or that both were occurring simultaneously. Since the number is between the two extremities of the species, it also indicates the possibility of evolution. Lucy also possessed a lumbar curve, another indicator of habitual bipedalism, and though 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 as it is quite indicative of bipedalism. (Terrie)

    A study of Lucy's mandibular structure indicated that Lucy's jaw was rather unlike other hominins, having a more gorilla-like appearance. Some scientists consider that this mandible structure arose "independently in gorillas and hominins", but that Au. Afarensis is therefore "too derived to occupy a position as a common ancestor of both the Homo and robust australopith clades". (PNAS)

    Abel was also discovered in 1995, Ardi in 1994, and Mrs. Ples in 1947 and have all contributed to closing the gap between man and beast.

    PNAS article: