Over half a century ago, researchers scouring the plains of Africa stumbled upon the fossilized remains of an ancient hominin from the genus Australopithecus afarensis dating back millions of years.

Today, all humans on Earth, including us, are descendants of the Homo-sapiens genus.

Despite the disappearance of various species from the homo genus, archaeologists have unearthed the fossilized remains of ancient humans. This has allowed paleontologists to study the long evolution which led to the emergence of homo sapiens.

Donald Johanson, an anthropologist from the US, had been searching the Afar region of Ethiopia in 1974 for fossilized animal bones when he and his student stumbled upon the remains of a tiny arm bone. This was the discovery of Lucy.

Forty-seven bones were unearthed in Ethiopia, making up nearly 40% of a complete skeleton. It’s now been almost five decades since the discovery, yet it remains the greatest breakthrough in the history of human paleontology.

Speaking on the evolution of hominins and the features that make us inherently human, Chris Stringer, a paleoanthropologist from the Natural History Museum of London, explained, “Human beings have three key attributes: our ability to walk upright, our capacity to make tools, and our large brains.”

Darwin’s “In The Descent of Man” proposes that the three human features, large brains, bipedalism, and tool-making, evolved in this order, suggesting that one played a role in the evolution of the next.

Lucy’s discovery revolutionized our understanding of human evolution, refuting Darwin’s idea that humans with larger brains came before our ancestors walked on two legs.

Stringers’ point was backed up by Zeresenay Alemseged, a palaeoanthropologist at the University of Chicago, who suggested that large brains were not a defining factor in what constitutes a human millions of years ago.

Lucy’s brain was only a bit bigger than an ape’s, but her hand was probably capable of smashing bones for marrow with crude tools, says Sonia Harmand of the French national research agency CNRS.

A question that continues to puzzle researchers is whether Lucy and her kin, the Australopithecus afarensis, meaning “the Southern Ape from Afar,” are the direct ancestors of Homo sapiens.

Despite some researchers suggesting the discovery of even older hominins likely means Lucy and her relatives were a side branch of the lineage that led to Homo sapiens, Alemseged disagrees, proposing that afarensis may be the originator of the lineage that led to modern humans.

Since the discovery of Lucy’s fossilized remains in the 70s, researchers have found afarensis in Tanzania, Chad, Kenya, and Ethiopia, and we know Lucy and her kin must have lived in these parts of Africa for close to a million years,” adds Alemseged.

Five decades of research found that Lucy walked upright despite her small brain and apelike upper body. While she likely climbed trees to feed, nest, or escape predators, Lucy was able to flourish and evolve through her offspring.

However, research has found that Lucy is no longer the earliest known member of the human family. Researchers believe that Lucy wasn’t alone in the grassy woodland.

While Lucy is more like a great-great-great-aunt than a direct human ancestor, her fossil is a better candidate for being the mother of every human being.

Lucy was the first hominin to push back the age of the human gene to a time closer to when geneticists thought the ancestors of humans had split from the ancestors of chimpanzees.

“Once upon a time, life was relatively simple because anything before 3 million years was A. afarensis … [and] it was the mother of us all,” says paleontologist Fred Spoor of the Natural History Museum in London. “That was the gospel.”

There was an intense search for Lucy’s ancestors in the Middle Awash region of Ethiopia in the mid-1990s. They found crushed but complete partial skeletons they named Ardipithecus ramidus, which dated back 4.4 million years ago.

Other fossils pushed the human lineage even further. A thighbone from an apparent upright walk from Kenya, called Millennium Man, dates back to 6 million years ago.

But what makes these upright walkers the great-great-great-grandparents of modern humans? It’s a fierce debate that anthropologists have been having for years. Are these species considered hominins, and how do they relate to Australopithecus.

Africa seems to be home to a diverse set of hominins, all of which are contenders to be the ancestors of Homo. One contender is the Kenyanthropus platyops, which has a flatter face and smaller molars than Lucy’s species.

Scientists believe that Lucy and other species, which would later help create modern humans, walked the Earth together between 2 and 3 million years ago.

Identifying the direct ancestor of Homo is challenging because “we don’t know much about early Homo,” says Carol Ward, a paleoanthropologist at the University of Missouri. The earliest known fossil of our genus is a lower jaw with worn molars from 2.8 million years ago.