Paleontology

Child of Lucy : A Closer Look at our Origins

The earliest, most complete skeleton of a child in the human lineage, discovered in a near-perfect fossilized state in Ethiopia, has now been identified by an international team of paleontologists as a hominid that dates back 3.3 million years.

The skull is so small it can be easily held in one hand, but its significance for paleontologists is enormous: The remains of this infant Australopithecus afarensis are expected to explain several key stages in the development of the early human species.

Australopithecus afarensis predated Neanderthals by more than three million years. Chronologically, they are situated roughly at the middle of a development timeline of the human species, which would begin with the earliest hominids–part human and part ape–seven million years ago, and end at the earliest pre-modern Homos, two million years ago.

The skull and the rest of the nearly complete juvenile skeleton were discovered in 2000 in a block of sandstone in the barren Dikika region of northeast Ethiopia, on a steep hill close to the Awash River. At that time, only the face of the cranium was exposed, and the bones were so completely encased in a cement-like covering that it has taken six years of painstaking and meticulous work to remove a significant amount of the coating without damage.

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© National Museum of Ethiopia, Addis Ababa

Analysis of the teeth and brain from “Selam's” skull indicates she was a girl, aged no older than three years.

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While “Selam”–as the child has since been named, after the word for “peace” in the Ethiopian language Amharic–unquestionably walked upright like other Australopithecus afarensis individuals, astonishingly, some of the bone morphology is more similar to that found in big African apes than in humans. Researchers believe it is the skeleton of a girl, and analysis of her canine teeth suggests she died when she was just three years old, although estimation of age will only be truly reliable once all teeth are extracted.

The remains of the infant's brain, not much bigger in a size-for-size comparison with that of a chimpanzee, crucially show that it was still in a state of development, displaying the human trait of a comparatively lengthy brain growth across a long period of childhood. But a study of the manual phalanges found them curled in an ape-like grasp, and the large upper hollow of the scapula, with the humerus joint cavity poised upwards, appears similar to that of a gorilla; The shape of the shoulders and the length of the arms suggest these body parts continued to play an occasional part in locomotion, and the finding opens a debate as to whether the afarensis were still tree-climbers. Opinion is divided as to whether the adaptation to walking on two feet would exclude arboreal locomotion, or whether retention of such primitive morphology would have been possible without it serving a continued, practical purpose. The surprise discovery of the hyoid, a tiny, curved throat bone which determines speech sounds, may yet unlock secrets of both how the afarensis communicated and how human speech evolved.

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© D. Geraads/CNRS Photothèque

Dikika site 1, in the Awash valley, Ethiopia, where “Selam's” skeleton was discovered.

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A geological study suggests “Selam” lived in an area of delta streams and a river which emptied into a freshwater lake, covering what is now an area of badlands. Faunal fossils found nearby, including those of giraffes, antelopes, white rhinoceros, crocodiles, three-toed equines, and rodents, indicate that the region was then made up of wooded savannah. It is likely that her corpse was washed away in a momentary flood of the area and quickly buried by sandstone sediment at the bottom of a water channel. Such a sequence of events would have protected the body from being dislocated by scavengers–and would explain the astonishing degree of skeletal preservation.

Work continues on freeing more bones of their sediment coating, and it is hoped that soon yet more significant details of this crucial stage of human evolution will be unveiled.

Graham Tearse