The Hadar research team in Ethiopia in 1974. Institute of Human Origins at Arizona State University

Fifty years ago, our understanding of human origins began to change with the discovery of Lucy, a remarkably complete, 3.2-million-year-old human relative unearthed from the sandy soil in Hadar, Ethiopia.

Lucy, formally known as A.L. 288-1, was about as tall as a kindergartner, with a body that blended features of apes and humans. Her Ethiopian name is Dinkinesh, which means “you are marvelous” in Amharic.

Understanding of human origins was still nascent in the 1970s. Fossils of hominins – the group that includes modern humans and our close ancestors – had been dated to 1.8 million years ago at Olduvai Gorge in Tanzania. A 2.5-million-year-old fossil of a hominin species called Australopithecus africanus had been discovered in South Africa. Lucy’s discovery on Nov. 24, 1974, by paleoanthropologist Donald Johanson, pushed things back nearly a million years, a major leap in scientific knowledge that still resonates a half-century later.

WHY LUCY DREW FAME

Many ancient human ancestors are known from fragments. But about 40 percent of Lucy’s skeleton was recovered, an extraordinary amount for a fossil of this age, which gave the public a way to imagine a shared human ancestor.

Lucy was identified as a member of a new species called Australopithecus afarensis. The debate over whether she was our ancestor, a grandmother to humanity and the missing link between apes and humans began instantaneously.

Debates over human evolution weren’t confined to the pages of esoteric scientific journals at the time – Johanson and fellow paleoanthropologist Richard Leakey sparred over their differing views in a televised debate hosted by Walter Cronkite in 1981.

Lucy quickly became a celebrity of the fossil record.

THE SEARCH FOR HUMAN ANCESTORS

As a kid growing up in Connecticut, Johanson got a book from a neighbor that planted an electrifying idea: “Someday, a fossil would be found of a human more apelike, or an ape more humanlike than had been found by anyone,” recalled Johanson, now a paleoanthropologist at Arizona State University.

From that moment, Johanson dreamed of going to Africa to search for this ancient connection, and in 1970 he began working there. In 1973, he discovered a knee joint from an unknown hominin species in Hadar. An orthopedic surgeon took one look and said there was no doubt that creature walked upright.

A year later, Johanson and graduate student Tom Gray were returning to camp when Johanson looked over his right shoulder and a piece of bone caught his eye. It was a piece of Lucy’s elbow – his childhood dream, at his feet. During the celebrations, the team played a Beatles tape and she was named for the song “Lucy in the Sky With Diamonds.”

The diminutive skeleton was remarkably complete, allowing scientists to understand how her body was built.

It also helped deconstruct the notion that humanlike traits had come on in concert – that a big brain had helped enable tool use, which required human ancestors to start walking upright so they could use their hands. Lucy had a small brain but was adapted to walking on two legs.

We now know that even more ancient hominins were bipedal, tracing back to at least 6 million years ago, when Orrorin tugenensis or Sahelanthropus tchadensis may have walked on two legs.

WALKING ON TWO FEET

Today, we see only our species of humans – Homo sapiens – and often wonder if our abilities and features are unique. Lucy’s body had similarities to apes and to modern-day humans.

Her pelvis was remarkably similar to the human version, clearly adapted for upright walking.

“If she walked down the street, you wouldn’t notice anything about her, except she is about 3½ feet tall,” said C. Owen Lovejoy, a distinguished professor of human evolutionary studies at Kent State University.

Scientists debate what Lucy’s body tells us about how she lived. Some believe that with long, strong arms and curved fingers, she still spent significant time in trees – and may have even died when she tumbled out of one. Others, including Johanson, disagree with that interpretation.

A BUSHY HOMININ FAMILY TREE

Not so long ago, new discoveries of ancient human fossil relatives might have been slotted into their spot in a tidy, linear timeline of human evolution, “a heroic and single-minded struggle from primitiveness to perfection,” in the words of paleoanthropologist Ian Tattersall. Lucy helped change that.

A reconstructed skeleton of Lucy is displayed next to Grace Latimer, 4, to illustrate Lucy’s small stature and brain size. Cleveland Museum of Natural History

Today, the map of early human evolution is much more complicated, and Lucy is one of a panoply of human ancestors in a complex and bushy family tree stretching back some 7 million years. Lucy was not the only Australopithecus. Even older than her, Ardipithecus – discovered in 1994 – blended apelike and humanlike characteristics. Side branches like Paranthropus appear in the fossil record, then disappear.

“The common conception is that we’re finding the grandmother [of humanity], and we’re never finding that,” said John Hawks, a paleoanthropologist at the University of Wisconsin at Madison. “Culturally, these are our ancestors – they are our connection to the past.”

A half-century later, an increasingly diverse group of scientists are studying and unearthing these ancestors.

“The big change, which is so rewarding to all of us, is there are Ethiopian scientists making their own major discoveries,” Johanson said.

After a controversial world tour in 2007, Lucy’s fragile bones are kept at home in the National Museum of Ethiopia in Addis Ababa.

The big question Lucy raised continues to fascinate scientists and the public across the world today: Where did we come from?