Post details: "Lucy" demoted from the human ancestral line

04/24/07

Permalinkby 11:48:24 am, Categories: Literature - Articles, 386 words   English (UK)

"Lucy" demoted from the human ancestral line

For as long as many of us can remember, Lucy has been an iconic fossil in the story of human evolution. The discussions about walking erect have been extensive. Many regard the evidence as definitive. However, "Rak and colleagues studied 146 mature primate bone specimens, including those from modern humans, gorillas, chimpanzees and orangutans and found that the "ramus element" of the mandible connecting the lower jaw to the skull is like that of the robust forms". The presence of this morphology in both Australopithecus robustus and Australopithecus afarensis and its absence in modern humans has "cast doubt on the role of [Lucy] as a common ancestor." Like a baton passed from runner to runner, the distinctive bone does the job of "eliminating the possibility that Lucy and her kind are Man's direct ancestors."
So what can be said about Lucy? "The specimen was only 1.1 meters tall, estimated to weigh 29 kilograms and look somewhat like a common chimpanzee." Also, "the structure of Lucy's mandibular ramus closely matches that of gorillas", which was an unexpected find, because this does not fit the previous cladistic analyses of chimps, gorillas and humans.
It looks like this is an appropriate time to reappraise the way museums and textbooks present the story of human evolution.

Gorilla-like anatomy on Australopithecus afarensis mandibles suggests Au. afarensis link to robust australopiths
Yoel Rak, Avishag Ginzburg, and Eli Geffen
Proceedings of the National Academy of Sciences USA, April 17 2007, 104: 6568-6572, doi 10.1073/pnas.0606454104

Abstract: Mandibular ramus morphology on a recently discovered specimen of Australopithecus afarensis closely matches that of gorillas. This finding was unexpected given that chimpanzees are the closest living relatives of humans. Because modern humans, chimpanzees, orangutans, and many other primates share a ramal morphology that differs from that of gorillas, the gorilla anatomy must represent a unique condition, and its appearance in fossil hominins must represent an independently derived morphology. This particular morphology appears also in Australopithecus robustus. The presence of the morphology in both the latter and Au. afarensis and its absence in modern humans cast doubt on the role of Au. afarensis as a modern human ancestor. The ramal anatomy of the earlier Ardipithecus ramidus is virtually that of a chimpanzee, corroborating the proposed phylogenetic scenario.

See also:
Siegel-Itzkovich, J. Israeli researchers: 'Lucy' is not direct ancestor of humans, THE JERUSALEM POST, Apr. 16, 2007

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