Australopithecus afarensis is a 3.18 million year old hominin, of the genus Australopithecus, of which the first 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.

Lucy's discovery

Don Johanson, an American anthropologist, and his team surveyed Hadar, Ethiopia during the late 1970’s for evidence in interpreting Human origins. On November 24, 1974 near the River Awash, Don was planning on updating his field notes but instead one of his students Tom Gray accompanied him to find fossil bones. Both of them were on the hot arid plains surveying on the dusty terrain when a fossil caught both their eyes; arm bone fragments on a slope. As they looked further, more and more bones were found including a jaw, arm bone, a thighbone, ribs, and vertebrae. Both Don and Tom raced back to their camp and began to complete the skeleton.

An amazing 40% of a skeleton was recovered, which, while sounding generally unimpressive, is astounding in the world of anthropology. When fossils are discovered usually only a few fragments are found, rarely any skulls or especially ribs are completely intact. Later that day Don Johnson and the team began closely analysing the skeleton and put it together, the Beatles song “Lucy in the sky with Diamonds” had played over on a small tape recorder that evening. Don noticed the feminine stature of the skeleton and noted that it was a female, thus he nicknamed it “Lucy” after the Beatles song. Lucy was only 3 feet 8 inches tall, weighed 29 kilograms (65 lbs) and looked somewhat like a Chimpanzee, but one crucial piece of evidence was noted that Lucy had walked upright like Humans do, her pelvis.

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 hominin 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.

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) and had a brain that was only around 400 cubic centimetres, i.e. she had developed a human trait without a large brain, which destroyed the 'big brain' theory.

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.

There previously had been problems in the past with designating Australopithecus afarensis as a bipedal hominin, because it is unknown for sure how this species walked. There are some anthropologists who don’t consider A. afarensis as bipedal because of the lack of evidence of Lucy’s skeleton. No direct conclusions can be made so far since a whole complete skeleton would need to be required to know for sure if and how Lucy walked upright. In fact these hominins may have occasionally walked upright but still walked on all fours like apes; the curved fingers on Australopithecus afarensis are similar to those of apes, which use them for climbing trees. These hominins were also much like modern Homo sapiens, they relied on the safety of trees from predators such as lions. Geologists know that 4 to 3 million years ago Eastern Africa began to change into open savannah, meaning that there were not as many trees to climb on, such as apes do in jungles. Hominims would eventually adapt to live as bipeds, unlike their ape cousins who live among the jungles.

Don Johanson claimed that Australopithecus afarensis was the first hominin to have existed from 3.9 to 3 million years ago, but earlier fossils have been found since; yet Lucy still remains a treasure among anthropologists who study Human origins. Older fossils have been uncovered but include only fragments and they face one major problem, no one knows for sure if they were neither 100% bipedal nor actually hominins, since there are no complete skeletons. Another major discovery made by Don Johnson was the “First Family” including 200 hominid fragments of A. afarensis discovered near Lucy on the other side of the hill. The site is known as site 333 by a count of fossil fragments uncovered such as teeth and pieces of jaw. 13 individuals were uncovered and all were adults, with no injuries caused by carnivores. All 13 individuals seemed to have died at the same time, thus Don concluded that they might have been killed instantly from a flash flood.

The minority Aquatic Ape Hypothesis makes the observation that when apes wade in water, they always walk bipedally. It suggests that bipedal hominins evolved from a population of apes occupying a semi-aquatic habitat, so that they waded or swam most of the time that 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 hominins had reoccupied land areas, but were now committed to upright bipedal walking.

Fossil sites

Australopithecus afarensis fossils have only been discovered within Eastern Africa which include Ethiopia (Hadar, Aramis), Tanzania (Laetoli) and in Kenya (Omo, Turkana, Koobi Fora and Lothagam).

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 hominins were concurrent with the Afar hominins. 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.