Our Origins

1. Discovery

In the early 1980s, a multidisciplinary team of geologists, paleoanthropologists, and archaeologists visited what they hoped would be a fossil-rich locality in the area around the village of Aramis, in the Middle Awash Valley of the Afar Depression of Ethiopia. Their hunch paid off when they found bits and pieces of fossils dating to the Pliocene epoch. Government restrictions prevented them from returning to the region until more than a decade later, but the wait was worth it. In 1992, the first field season, they found a hominid tooth and some other skeletal parts. The place clearly held great promise for fossil hunting. From 1995 to 2005, scientists and field workers literally crawled across the landscape on their hands and knees in search of hominids and other fossils, in geological deposits dating to 4.4 mya. This herculean effort had an enormous payoff, producing one of the most important fossil records of early hominids ever found and an abundant record of plant and animal fossils dating to the same time.  Study of the plant and animal fossils revealed that these early hominids inhabited a cool, wet forest.

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2. Recovery

Once the fossils’ locations had been recorded, it was important to remove the fossils as quickly as possible. Because the bones were soft, they had to be treated with preservatives, and some had to be removed in plaster jackets. They were taken first to the field camp and eventually to the laboratory at the National Museum in Addis Ababa, Ethiopia, for detailed study. The 109 hominid fossils represented 36 individuals. Among them was the most exciting discovery—one of the most important in the history of paleoanthropology—a partial skeleton, field number ARA-VP-6/500. The oldest fossil hominid skeleton yet found, it predates Lucy’s skeleton, from Hadar, Ethiopia, by more than a million years. It took the researchers three years of hard work to recover the remains of this skeleton alone.   

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3. Lab Work

Almost from the beginning of the discovery of fossils in this locality some years before, it was clear that they needed a new name. Tim White called the species Ardipithecus ramidus (in the local Afar language, ardi means “ground” or “floor” and ramid means “root”).  The partial skeleton, nicknamed “Ardi” by the field team, required years of cleaning, preparation, and reconstruction. For example, to assemble all the skull fragments into an accurate reconstruction, casts of each of the scores of pieces were made. The resulting images were combined with digital images to produce a composite picture (see inset). Various indicators, including the size of the body, revealed that the hominid was a female adult, weighing 50 kg (110 lbs) and standing 120 cm (4 ft) high.

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4. Understanding Ardi: Head to Toe

Image: Jay Matternes

Skull and Teeth: The skull is very similar to those of other pre-australopithecines, such as Sahelanthropus, with its tiny brain (300−350 cc) and projecting face. It is probably like the skull of the nearest common ancestor of apes and humans. The teeth show none of the specializations seen in living apes, such as the big incisors and canines and sectorial complex of orangutans and chimpanzees. Wear on the teeth suggests that the hominid was omnivorous, eating nonabrasive foods and some hard foods. The canine shows no functional honing, and so these hominids processed their food like later hominids. 

Upper limb and hand: Especially striking about the upper limb and hand are their primitiveness. Compared with those of living humans, the forearm (radius and ulna) is extraordinarily long in relation to the upper arm. The elbow joint shows no evidence that these arms were used for suspension, however. The size and morphology of the hand indicate that the hominid did not knuckle-walk. Thus knuckle-walking evolved in later apes. The fingers are quite long and had excellent grasping capability. Ardi walked on her palms when in the trees.

Pelvis:  The wide pelvis indicates full hominid status: Ardi walked bipedally when on the ground. In this respect, the pelvis is quite evolved, especially compared with the upper limb/hands and lower limb/feet. The lower part of the pelvis reveals evidence of muscles used in climbing. 

Lower limb: The lower limb and foot are adapted for bipedality, but they also reveal characteristics that indicate significant time spent in the trees. For example, the foot has greatly elongated toes and a fully divergent big toe for grasping. No later hominid has this particular combination of features. While retaining its very primitive grasping capability, the foot also served in propelling the body forward when walking or running on the ground.  Like the other parts of the skeleton, it is a mosaic of primitive and derived characteristics. In combination, these characteristics show a hominid that was more primitive in its locomotor pattern than the australopithecines.

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5. Implications for Human Evolution

This remarkable hominid skeleton, along with the other fossils found at Aramis, provides us with a new understanding of the origins and evolution of the human and ape lineages. This new understanding is made possible by this remarkably complete fossil record and the unprecedented level and detail of multidisciplinary study, ranging from habitat reconstruction to the analysis of function and behavior of early hominids. The very primitive nature of this skeleton confirms that the divergence of the chimpanzee/human lineage was quite recent—somewhere around 7 million years ago—and provides insight into behavior and adaptation soon after the divergence. This fossil is the closest found yet to the common ancestor of chimpanzees and humans. Most importantly, all earlier models suggesting a chimpanzeelike ancestor for hominids are incorrect—the first hominid was not chimpanzeelike.  Based on the record of Ardipithecus fossils found to date, there was little difference in body size between males and females.

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Further Reading

View National Geographic’s interactive page about the Ardi discovery.   From this page, you also navigate to a feature article and a photo gallery.

The authors of the technical reports have published excellent summary articles in the October 2, 2009, issue of Science magazine. Also presented there are the skeleton and reconstructions of what Ardi looked like in life.  

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