At 3.2 million years old, her part-human, part-apelike skeleton stands just 3 feet 8 inches tall, yet she is known as "the wondrous one" in Ethiopia, where she was discovered.
Her other name is Lucy, and at the time of her discovery in 1974 she was the oldest, most complete fossil human ancestor ever found. Her discovery brought new insights into human evolution for both scientists and the public. [Learn more about Lucy]
AAAS Fellow William Kimbel first laid eyes on Lucy in 1975 when he was an undergraduate student at Case Western Reserve University.
Lucy was on loan from the Ethiopian government for study at the Cleveland Museum of Natural History. Kimbel's professor, Donald Johanson, responsible for the groundbreaking discovery of Lucy, gave the young student the rare opportunity to examine her.
"Her antiquity and completeness, not to mention the genius of her nickname [which came from the popular Beatles song], made her an instantly recognizable icon for the study of early human evolution," he says.
That chance encounter would inspire him to spend the next four decades looking for and researching her species.
Lucy's completeness gave researchers evidence of aspects of evolution that had previously been theoretical. Most especially, she verified the idea that human evolution occurred mosaically, meaning that human traits did not all develop at the same time. She proved instead that the earliest hominins had both human and apelike characteristics. Like humans, they were advanced terrestrial bipeds, walking upright on two legs on the ground; like apes, they had extremely primitive teeth and skulls.
For non-scientists, Kimbel says Lucy's discovery essentially made human evolution real.
"Being able to study Lucy...firsthand and up close was, for me, full realization of the promise of future discoveries," Kimbel says.
Today, as director of Arizona State University's Institute of Human Origins, Kimbel specializes in the evolution of Australopithecus, the genus to which Lucy's afarensis species belongs. He is interested in the last four million years in human evolution, especially hominoid skulls, which show complex evolutionary changes in diet, posture and brain size.
Kimbel conducts fieldwork in Hadar, Ethiopia, where Lucy was discovered. "It's barren, hot and sparsely populated," he says. "Much of the area is terrifically rich in fossils, which makes it incredibly exciting to work there."
He's dedicated to increasing the sample size of A. afarensis, of which there are currently 375 specimens. "Variation is the raw material of evolution," he observes. "To interpret the past accurately, we must obtain a good idea of how human ancestral populations varied across time and space."
Hadar is best known for its early hominid fossils, including all known A. afarensis fossils and an unknown hominid species, possibly Homo habilis. Kimbel's team also has uncovered an upper jaw of an early Homo specimen and Oldowan stone tools that date to 2.35 million years ago.
His research will help paleoanthropologists answer questions about lines of descent and further map out the human evolutionary tree. Already, far older fossils than Lucy have allowed scientists to map that tree back 6 million years.
Kimbel encourages scientists to publicize research on the origin of species to help decrease public ignorance. "It's important to understand that we share a unity with the natural world, and how we're responsible for that world that we have come to dominate," he says.
Lucy, "the wondrous one," is a vital bridge between early human life and modern existence, opening up scientific exploration—and public imagination—about 3.2 million years of human life.