A Science Odyssey
People and Discoveries
photo Johanson finds 3.2 million-year-old Lucy

Photo: X-ray photo of the "Lucy" skeleton

In 1973, Donald Johanson was in the Afar, part of the Hadar region of Ethiopia, with the International Afar Research Expedition. He made a dramatic fossil find -- the leg bones of 3-million-year-old hominid. The bones' size and shape indicated that this individual walked upright, making it the oldest hominid on record to do so. This discovery helped Johanson raise enough money to continue the expedition in the Afar.

On November 30, 1974, Johanson and another member of the expedition discovered small bones from one individual -- it was a hominid, but looked different from any they were familiar with. Everyone at the site joined in the search for more of this specimen and collected hundreds of pieces. The pieces did appear to be from the same individual, and made up 40 percent of a skeleton. The pelvis showed it had been a female, and the team named her Lucy after the Beatles' song "Lucy in the Sky with Diamonds."

Lucy had a small brain and was only about one meter tall. Since bones from both left and right sides were found, mirror images could be constructed to put together 70 percent of her skeleton. More than one dating technique put her age at about 3.5 million years. (Johanson's earlier leg bone find was dated at 4 million years old.) The team kept working at the site and found other, more modern hominids together with stone tools. By 1976, however, Ethiopia's political situation was unstable, making further excavations unsafe or impossible.

In 1978, Mary Leakey discovered ancient footprints preserved in the ground around what was once a water hole at Laetoli, Tanzania. These prints showed clearly that small primates walked on two feet there. This put upright walking even further back in time.

Johanson and his colleague Tim White compared Leakey's finds at Laetoli with theirs from Afar, and felt that they were very similar, probably representing a stage between apes and humans. They categorized them both as Australopithecus afarensis. Leakey disagreed, but both of their finds broke a long-standing assumption: that humans developed big brains before walking upright. After 1974, scientists realized that this wasn't necessarily true, and that brain size overlaps between types of hominids, even as modern people's brains vary in size without relation to intelligence. This meant they had to look again at why hominids started walking upright. It had been thought that the big-brained creatures started using tools, and to free up their hands, they had to walk upright. But Lucy walked on two feet, and even had "modern" hands, yet showed no evidence of using tools.

Opponents of Johanson and White's theory think the Homo genus had a separate lineage from other primates. Johanson acknowledged that his explanation would be subject to change with new evidence.

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