Lucy Reconstruction Models

Lucy is among the most famous fossil skeletons believed to represent an early stage of hominid evolution following separation of the human lineage from [Page 1501]its nearest living ape relative. At 3.2 million years, Lucy was the oldest and most complete hominid skeleton that clearly showed evidence of bipedal locomotion. The label “Lucy” provided a personal metaphor for an individual believed to be a female approximately 20 years of age at the time of her death. Classified as Australopithecus afarensis,Lucy was one of nine species clustered under the genus Australopithecus despite a poor understanding of their evolutionary relationships and status.

Numerous portraits of the australopiths have combined the constraints of fossil morphology with the addition of soft tissue features that are imagined to be present based on the presumption that Lucy and other early hominids resembled those apes most closely related to humans. Because those apes are widely believed to be chimpanzees, based on the similarity of DNA base sequences between chimpanzees and humans, the soft tissues assigned to Lucy are those of chimpanzees. Lucy and other early hominids are given the fleshy nostrils unique to chimpanzees and gorillas among the living primates. The body hair is short and dark and projects away from the face as with chimpanzees, and there are no beard and mustache present in males because it is not found in chimpanzees. Instead, sparse hair is shown on the underside of the lower jaw, whereas the forehead is imagined to be free of hair as with humans but unlike chimpanzees.

Although the soft tissues may be a matter of conjecture, the hard tissues offer some constraints that are problematic for any chimpanzee reconstruction for Lucy and other australopiths. The forward-projecting brow ridge extending across and between the eyes that gives chimpanzees and gorillas that classic hooded appearance is missing. Instead, the ridges of Lucy and other australopiths are limited to the region immediately above the eye. Neither do the eyebrow ridges project forward in the manner of chimpanzees and gorillas. Also absent is the channel or sulcus that lies immediately behind the brow ridges in chimpanzees and gorillas. In addition to the absence of these African ape features is the presence of a different kind of cheekbone. The cheekbone of the chimpanzee is narrow and slopes back along the lower margin. The complete opposite is found in australopiths, where the cheekbone is very broad and is vertical or slopes forward at the lower margin.

The combination of these three features is hardly congruent with what might be expected of a chimpanzee ancestry for humans. When artists add chimpanzee features in their reconstructions of australopiths, the result is a very incongruous bipedal “chimpanzee” that has massively broad cheekbones and lacks the classic supraorbital ridge (torus) and posttoral depression of African apes. Perhaps their absence may be attributed to an evolutionary loss of the features since separation from the common ancestor with chimpanzees, whereas the cheekbones are just a novel development that was then later lost in the evolution of Homo. This ad hoc scenario may be all well and good, but there is another great ape that shows no such contradictions in skull structure.

Source: © Robert Jurmain.

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