Lucy (Australopithecus)

Discovery

French geologist and paleoanthropologist Maurice Taieb discovered the Hadar Formation for paleoanthropology in 1974 in the Afar Triangle of Ethiopia; he recognized its potential as a likely repository of the fossils and artifacts of human origins. Taieb formed the International Afar Research Expedition (IARE) and invited three prominent international scientists to conduct research expeditions into the region. These were: Donald Johanson, an American paleoanthropologist and curator at the Cleveland Museum of Natural History, who later founded the Institute of Human Origins, now part of Arizona State University; Mary Leakey, the noted British paleoanthropologist; and Yves Coppens, a French paleoanthropologist now based at the Collège de France. An expedition was soon mounted with four American and seven French participants; in the autumn of 1973 the team began surveying sites around Hadar for signs related to the origin of humans.

In November 1971, near the end of the first field season, Johanson noticed a fossil of the upper end of a shinbone, which had been sliced slightly at the front. The lower end of a femur was found near it, and when he fitted them together, the angle of the knee joint clearly showed that this fossil, reference AL 129-1, was an upright walking hominin. This fossil was later dated at more than three million years old – much older than other hominin fossils known at the time. The site lay about 2.5 kilometres (1.6 mi) from the site where "Lucy" subsequently was found, in a rock stratum 200 feet (61 m) deeper than that in which the Lucy fragments were found.

The team returned for the second field season the following year and found hominin jaws. Then, on the morning of 24 November 1974, near the Awash River, Johanson abandoned a plan to update his field notes and joined graduate student Tom Gray to search Locality 162 for bone fossils.

By Johanson's later (published) accounts, both he and Tom Gray spent two hours on the increasingly hot and arid plain, surveying the dusty terrain. On a hunch, Johanson decided to look at the bottom of a small gully that had been checked at least twice before by other workers. At first view nothing was immediately visible, but as they turned to leave a fossil caught Johanson's eye; an arm bone fragment was lying on the slope. Near it lay a fragment from the back of a small skull. They noticed part of a femur (thigh bone) a few feet (about one meter) away. As they explored further, they found more and more bones on the slope, including vertebrae, part of a pelvis, ribs, and pieces of jaw. They marked the spot and returned to camp, excited at finding so many pieces apparently from one individual hominin.

In the afternoon, all members of the expedition returned to the gully to section off the site and prepare it for careful excavation and collection, which eventually took three weeks. That first evening they celebrated at the camp; at some stage during the evening they named fossil AL 288-1 "Lucy", after the Beatles' song "Lucy in the Sky with Diamonds", which was being played loudly and repeatedly on a tape recorder in the camp.

Over the next three weeks the team found several hundred pieces or fragments of bone with no duplication, confirming their original speculation that the pieces were from a single individual; ultimately, it was determined that an amazing 40 percent of a hominin skeleton was recovered at the site. Johanson assessed it as female based on the one complete pelvic bone and sacrum, which indicated the width of the pelvic opening.

Lucy was 1.1 m (3 ft 7 in) tall, weighed 29 kg (64 lb), and (after reconstruction) looked somewhat like a chimpanzee. The creature had a small brain like a chimpanzee, but the pelvis and leg bones were almost identical in function to those of modern humans, showing with certainty that Lucy's species were hominins that had stood upright and had walked erect.

With the permission of the government of Ethiopia, Johanson brought all the skeletal fragments to the Cleveland Museum of Natural History in Ohio, where they were stabilized and reconstructed by anthropologist Owen Lovejoy. Lucy the pre-human hominid and fossil hominin, captured much public notice; she became almost a household name at the time. Some nine years later, and now assembled altogether, she was returned to Ethiopia.

Additional finds of A. afarensis were made during the 1970s and forward, gaining for anthropologists a better understanding of the ranges of morphic variability and sexual dimorphism within the species. An even more complete skeleton of a related hominid, Ardipithecus, was found in the same Awash Valley in 1992. "Ardi", like "Lucy", was a hominid-becoming-hominin species, but, dated at 4.4 million years ago, it had evolved much earlier than the afarensis species, and there is debate about whether Ardipithecus achieved full status as a hominin. Excavation, preservation, and analysis of the specimen Ardi was very difficult and time-consuming; work was begun in 1992, with the results not fully published until October 2009.

Age estimates of the Lucy fossil

Initial attempts were made in 1974 by Maurice Taieb and James Aronson in Aronson's laboratory at Case Western Reserve University to estimate the age of the fossils using the potassium-argon radiometric dating method. These efforts were hindered by several factors: the rocks in the recovery area were chemically altered or reworked by volcanic activity; datable crystals were very scarce in the sample material; and there was a complete absence of pumice clasts at Hadar. (The Lucy skeleton occurs in the part of the Hadar sequence that accumulated with the fastest rate of deposition, which partly accounts for her excellent preservation.)

Fieldwork at Hadar was suspended in the winter of 1976–77. When it was resumed thirteen years later in 1990, the more precise argon-argon technology had been updated by Derek York at the University of Toronto. By 1992 Aronson and Robert Walter had found two suitable samples of volcanic ash – the older layer of ash was about 18 m below the fossil and the younger layer was only one meter below, closely marking the age of deposition of the specimen. These samples were argon-argon dated by Walter in the geochronology laboratory of the Institute of Human Origins at 3.22 and 3.18 million years.

Ambulation

One of the most striking characteristics of the Lucy skeleton is a valgus knee, which indicates that it, or "she", normally moved by walking upright. Her femur presents a mix of ancestral and derived traits. The femoral head is small and the femoral neck is short; both are primitive (that is, ancestral) traits. The greater trochanter, however, is clearly a derived trait, being short and human-like – even though, unlike in humans, it is situated higher than the femoral head. The length ratio of her humerus (arm) to femur (thigh) is 84.6%, which compares 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 both were occurring simultaneously. Lucy also had a lordose curve, or lumbar curve, another indicator of habitual bipedalism. She apparently had physiological flat feet, not to be confused with pes planus or any pathology, even though other afarensis individuals appear to have had arched feet.

Pelvic girdle

Johanson recovered Lucy's left innominate bone and sacrum. Though the sacrum was remarkably well preserved, the innominate was distorted, leading to two different reconstructions. The first reconstruction had little iliac flare and virtually no anterior wrap, creating an ilium that greatly resembled that of an ape. However, this reconstruction proved to be faulty, as the superior pubic rami would not have been able to connect were the right ilium identical to the left.

A later reconstruction by Tim White showed a broad iliac flare and a definite anterior wrap, indicating that Lucy had an unusually broad inner acetabular distance and unusually long superior pubic rami. Her pubic arch was over 90 degrees and derived, that is, similar to modern human females. Her acetabulum, however, was small and primitive.

Cranial specimens

The cranial evidence recovered from Lucy is far less derived than her postcranium. Her neurocranium is small and primitive, while she possesses more spatulate canines than apes. The cranial capacity was about 375 to 500 cc.

Rib cage and plant-based diet

Australopithecus afarensis seems to have had the same conical rib-cage found in today's great apes (like the chimpanzee and gorilla), which allows room for a large stomach below and indicates the longer intestine needed for digesting voluminous plant matter. Fully 60% of the blood supply of great apes is used in the digestion process, greatly impeding the development of brain function (which is limited thereby to using about 10% of the circulation). The heavier musculature of the jaws – those muscles operating the intensive masticatory process for chewing plant material – similarly would also limit development, here of the skull (braincase). During evolution of the human lineage these muscles seem to have weakened with the loss of the myosin gene MYH16, a two base-pair deletion that occurred about 2.4 million years ago.

Other findings

A study of the mandibile across a number of specimens of A. afarensis indicated that Lucy's jaw was rather unlike other hominins, having a more gorilla-like appearance. Rak et al. concluded that this morphology arose "independently in gorillas and hominins", and that A. afarensis is "too derived to occupy a position as a common ancestor of both the Homo and robust australopith clades".

Age at death

Lucy's cause of death cannot be determined. The specimen does not show the signs of post-mortem bone damage characteristic of animals killed by predators and then scavenged. The only visible damage is a single carnivore tooth mark on the top of her left pubic bone, believed to have occurred at or around the time of death, but which is not necessarily related to her death. Her third molars were erupted and slightly worn and therefore, it was concluded that she was fully matured with completed skeletal development. There are indications of degenerative disease to her vertebrae that do not necessarily indicate old age. Some believe Lucy died from falling off a tree. It is believed that she was a mature but young adult when she died, about 12 years old.

In 2016 researchers at the University of Texas at Austin suggested that Lucy died after falling from a tall tree. Donald Johanson and Tim White disagreed with the suggestions.

Exhibitions

The Lucy skeleton is preserved at the National Museum of Ethiopia in Addis Ababa. A plaster replica is publicly displayed there instead of the original skeleton. A cast of the original skeleton in its reconstructed form is displayed at the Cleveland Museum of Natural History. At the American Museum of Natural History in New York City a diorama presents Australopithecus afarensis and other human predecessors, showing each species and its habitat and explaining the behaviors and capabilities assigned to each. A cast of the skeleton as well as a corpus reconstruction of Lucy is displayed at The Field Museum in Chicago.

US tour

A six-year exhibition tour of the United States was undertaken during 2007–13; it was titled Lucy’s Legacy: The Hidden Treasures of Ethiopia and it featured the actual Lucy fossil reconstruction and over 100 artifacts from prehistoric times to the present. The tour was organized by the Houston Museum of Natural Science and was approved by the Ethiopian government and the U.S. State Department. A portion of the proceeds from the tour was designated to modernizing Ethiopia's museums.

There was controversy in advance of the tour over concerns about the fragility of the specimens, with various experts including paleoanthropologist Owen Lovejoy and anthropologist and conservationist Richard Leakey publicly stating their opposition. For these reasons, The Smithsonian Institution and Cleveland Museum of Natural History and other museums declined to host the exhibits.

The fossil's discoverer Don Johanson stated his concern for the possibility of damage, but did not oppose touring and exhibiting Lucy, as he felt it would raise awareness of human-origins studies. The Houston Museum made arrangements for exhibiting at ten other museums, including the Pacific Science Center in Seattle. In September 2008, between the exhibits in Houston and Seattle, the skeletal assembly was taken to the University of Texas at Austin for 10 days to perform high resolution CT scans of the fossils.

Lucy was exhibited at the Discovery Times Square Exposition in New York City from June until October 2009. In New York, the exhibition included Ida (Plate B), the other half of the recently announced Darwinius masilae fossil.

Ethiopia celebrated the return of Lucy in May 2013.

In popular culture

On November 24, 2015, Lucy was honored with a Google Doodle.