Australopithecus afarensis? |
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Lucy: Australopithecus afarensis Conservation status: Fossil |
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Lucy skeleton cast, American Museum of Natural History Lucy skeleton cast, American Museum of Natural History |
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| Australopithecus afarensis Johanson & White, 1978 |
Lucy is a 3.18 million year old female hominid, of the genus Australopithecus, whose skeleton was discovered on November 24, 1974 by Donald Johanson, Yves Coppens and Tim White in the Afar Depression of Ethiopia. They named it "Lucy" in reference to the famous Beatles song "Lucy in the Sky with Diamonds", which was played as they celebrated the find. Donald Johanson brought the skeleton (an unprecedented 40% complete) back to Cleveland, under agreement with the government of the time in Ethiopia, and returned it according to agreement some 9 years later.
Lucy was the first fossil hominid to really capture public notice, becoming almost a household name at the time.
Current opinion is that the Lucy skeleton should be classified in the species Australopithecus afarensis.
Lucy is preserved at the national Museum in Addis Ababa, Ethiopia. A plaster replica is displayed instead of the original skeleton. A diorama of Australopithecus afarensis and other human predecessors showing each species in its habitat and demonstrating the behaviors and capabilities that scientists believe it had is in the Hall of Human Biology and Evolution at the American Museum of Natural History in New York City.
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Physical characteristics
Chimp-sized brain
One of the most striking characteristics possessed by Lucy was that she had a small skull, bipedal knee structure, and molars and front teeth of human (rather than great ape) style and relative size, but a small skull and small body. The image of a bipedal hominid with small skull, but teeth like a human, was somewhat shocking to the paleoanthropological world at the time.
This was because during the period 1950-1970 it was believed that the development of a brain larger than an ape brain was the trigger that caused apes to evolve into humans. Before Lucy, a fossil called '1470', with a brain capacity of about 800 cubic centimetres had been discovered, an ape with a bigger brain, and if the 'big brain' theory was correct, then all humans should have evolved from 1470. However, it turned out Lucy was older than 1470, yet Lucy had bipedalism (she walked upright), i.e. she had developed a human trait without a large brain, which destroyed the 'big brain' theory. Lucy's brain was only around 400 cubic centemeters.
Bipedalism
There are differing views on how Lucy or her ancestors first became bipedal full-time.
The so-called 'savannah theory' on how A. afarensis evolved bipedalism hangs on the evidence that around 6 - 8 million years ago there seems to have been a mass extinction of forest dwelling creatures. This triggered a burst of 'adaptive radiation', an evolutionary characteristic that generates new species quickly. Lucy's 'grandparents' were tree dwelling apes, but in Lucy's world the trees would have gone, and Lucy would have been forced to find a living on the flat treeless savanna. Being bipedal would have had evolutionary advantages - for example, with the eyes higher up, she could see further than quadrupeds. The disadvantages of bipedalism were great - Lucy was the slowest moving primate of her time, for example, but the advantages of bipedalism must have outweighed the disadvantages.
The minority Aquatic Ape Hypothesis makes the observation that when apes wade in water, they always walk bipedally. It suggests that bipedal hominids evolved from a population of apes occupying a semi-aquatic habitat, so that they waded or swam all the time they were active, and rested in trees at night. Over generations they became more and more upright, and lost the ability to walk quadrupedally. By Lucy's time, the hominids had reoccupied land areas, but were now committed to upright bipedal walking.
Related work
Further finds at Afar, including the many hominid bones in "site 333", produced more bones of concurrent date, and led to Johanson and White's eventual argument that the Koobi Fora hominids were concurrent with the Afar hominids. In other words, Lucy was not unique in evolving bipedalism and a flat face.
Recently, an entirely new species has been discovered, called Kenyanthropus platyops. This has the same characteristics as Lucy, but is possibly an entirely different genus.
Another species, called Ardipithecus ramidus, has been found, which was fully bipedal, yet appears to have been contemporaneous with a woodland environment, and, more importantly, contemporaneous with Australopithecus afarensis. We do not yet have an estimate of the cranial capacity of A. ramidus, however.