Fifty Years Later: How Lucy, the Mother of Mankind, Changed the View of Evolution

In 1974, the fossilized bones of Lucy, a 3.2 million year old hominin, were discovered in Ethiopia. How did this amazing skeleton disprove Darwin's theory and what links it to the Beatles band?

On November 24, 1974, American anthropologist Donald Johanson was wading through a ravine in Hadar in the Afar region of Ethiopia with his student Tom Gray. The pair were searching for fossilized animal bones in the surrounding silt and ash when Johanson spotted a tiny fragment of a hand bone - and realized it belonged to a humanoid creature.

"We looked up the slope," Johanson later recalled. "There, strangely enough, lay a lot of bone fragments - a nearly complete lower jaw, femur, ribs, vertebrae, and more! Tom and I screamed and hugged each other and danced, as mad as any Englishman in the midday sun!""

Johanson and Gray returned to their camp, jubilant, with the hum of their Land Rover. Beer was chilled in the Awash River and roast goat meat was served to celebrate the discovery, which by all accounts was sensational. In total, Johanson and Gray discovered 47 bones from a single ancient hominin (a term used to define humans and all our extinct bipedal relatives).

The fragments they collected amounted to about 40% of the complete skeleton, and subsequent dating showed the remains to be about 3.2 million years old. At the time, it was the oldest humanoid creature ever discovered by fossil hunters, and she was given the name Lucy.

Fifty years later, Johanson and Gray's discovery remains one of the most notable breakthroughs in human paleontology. Judging from the pelvis, the scientists concluded that it was a woman, and the short legs indicated that it was only 1.2 meters tall. This discovery was followed by other similar finds, some in Ethiopia and some in Tanzania, and in 1978 Johanson and his colleague Tim White announced that all of these bones, including Lucy's, belonged to a single, previously unknown hominin species, which they named Australopithecus afarensis - "Southern Ape of Afar."

Johansoni White placed Australopithecus afarensis at the base of an ancestral tree that led to later species such as Homo erectus and then Neanderthals and Homo sapiens. From this perspective, Lucy was the mother of humankind.

And while subsequent research and other fossil finds have led to some reconsideration of Lucy's exalted status, the very fact that she walked upright despite her small brain was - in and of itself - a discovery of great importance, says paleoanthropologist Chris Stringer of the Natural History Museum in London.

"Human beings have three key features: the ability to walk upright, the ability to make tools, and a large brain," Stringer says. "But the crucial question is, which of these features came first in our evolution? What was the first step that set our ancestors on the path that eventually led to Homo sapiens?""

In The Origin of Man, Charles Darwin argued that three human traits - bipedality, tool-making, and large brains - evolved in concert, with the development of one stimulating the further evolution of the others. On this basis, an enlarged brain must have been part of human evolution from the beginning.

Then Lucy was discovered. "Lucy showed that this idea is simply not true," Stringer says. "Her skeleton showed that our ancestors walked on two legs long before their brains got big."

This view is supported by Zeresenay Alemseged, a paleoanthropologist at the University of Chicago. "Lucy has shown that a large brain was not a prerequisite for belonging to the human species," he says.

It's an intriguing observation that raises key questions. Why did our ancestors stand on two legs in the first place? What evolutionary advantages did they gain by standing on two legs?

Many answers have been proposed over the years. Walking on two legs, the monkeys would have been free to pick fruit from low-lying branches and carry food and children. Standing upright would have made them look larger and more intimidating, while reducing the rays of the harsh African sun falling on their backs.

All of these speculations are suggestive, although the most likely cause was more prosaic, Alemseged argues. "When you walk on two legs rather than four, you save energy. It's very simple. You expend fewer calories - and don't forget that our early ancestors didn't struggle to gain weight like we do today. They needed to get all the energy they could get and use it to the best of their ability. Walking on two legs helped them do that."

On the other hand, humans reap the benefits in the form of brain enlargement that eventually followed the transition to bipedalism.

Lucy's discovery allowed Australopithecus afarensis to take center stage in the history of human evolution. However, since its presence was first discovered at Hadar, numerous fossils of other, even older hominin species have been found.

These include Australopithecus anamensis, which four million years ago roamed the terrain of what is now Kenya and Ethiopia, and Ardipithecus ramidus, which lived about 4.5 million years ago in a similar area of Africa. Importantly, anatomical features of these early apes indicate that they walked on two legs.

So could one of these species - and not Australopithecus afarensis - have been the true ancestor of the lineage that led to Homo sapiens? Lucy's lineage could have simply been a side branch of that family tree, rather than a direct link to modern humans. In other words, was Lucy merely humanity's great aunt, not its mother? Some scientists believe she was.

Alemseged, however, doubts this. "These early hominins probably walked upright for some time, but many of them probably lived most of their lives in trees. In contrast, Lucy and her afarensis relatives spent a lot of time walking upright. They played a crucial role in transforming our genus into one that has become committed to upright posture."

With the advent of Lucy, the human species reached the stage where walking upright became commonplace. Humans became bipedal animals, a defining feature of the species that eventually gave rise to Homo sapiens.

Alemseged's own contribution to the field is that on December 10, 2000, he discovered Selam, a nearly complete fossil skull and skeletal parts of a child Australopithecus afarensis. It is sometimes referred to as "Dikika's baby" or "Lucy's baby," although the latter claim is erroneous, as the skull is 3.3 million years old, which means it is more than 100,000 years older than Lucy.

"We have found afarensis in Tanzania, Chad, Kenya and Ethiopia and know that Lucy and her relatives have lived in these parts of Africa for about a million years," Alemseged adds. "Such antiquity and wide geographic distribution convince me that this is the most likely candidate to give rise to multiple species of the genus Homo and eventually our own species, Homo sapiens."

Lucy's remains are now housed at the National Museum of Ethiopia in Addis Ababa, where Ethiopian-born Alemseged made headlines in 2015 when he showed Lucy to Barack Obama during the president's state visit. "She is the predecessor of all modern humans," he told Obama. "Every human being, even Donald Trump."

Other scientists are more cautious about Lucy's exact relationship to modern humans. "The problem is that we have only two areas where we have good fossil evidence of hominin evolution: in the rift valley regions of Kenya, Tanzania and Ethiopia, and in South Africa," Stringer notes.

"In the former case, there are lakes, rivers and sediments where it is relatively easy to find fossils, and in South Africa there are many caves where early hominins were fossilized. This gives a very biased picture of hominin evolution in Africa. We don't know what happened in other parts of the continent," Stringer adds. "It's like a drunk man looking for his keys at night, and only looks where there are street lights - because those are the only places he can see."

There is currently a lack of places to find fossilized remains in Africa, and places where people actually searched, and this limits the amount of evidence researchers can gather about exactly how human evolution occurred millions of years ago.

Nevertheless, it is clear that Lucy was able to play an important role in developing an understanding of her own species - although her naming was rather haphazard, as Johanson admits in her recollection of the exciting days that followed her discovery at Hadar.

"Surely such a noble little fossil lady deserves a name, we thought, and one evening as we sat listening to Beatles songs, someone said: "Why don't we name her after Lucy? You know, after Lucy from the song " Lucy in the Sky with Diamonds"." So she became Lucy," Johanson says.

However, as Caitlin Schrein points out in Nature, there may well have been a very different title. The Beatles song was recorded seven years earlier. And if Johanson and his colleagues had chosen pop music in a more modern way, or had more accessible recordings, they probably would have listened to more contemporary compositions.

The songs could even include hits from 1974 - like John Denver's "Annie's Song" or "Benny and the Supersonic Jets" Elton John. If they had listened to these songs, the world's most famous fossil skeleton might have a different name.