Fifty Years Later, How Lucy, the Mother of Humanity, Changed Our Understanding of Evolution

On November 24, 1974, American anthropologist Donald Johanson and his research student Tom Gray were rummaging through a ravine near Hadar in the Afar region of Ethiopia. The pair were searching for fossilized animal bones in the surrounding silt and ash when Johanson spotted a small fragment of an arm bone—and realized it belonged to a human-like creature.

“We looked up the slope,” Johanson later recalled. “There, unbelievably, lay a multitude of bone fragments – an almost complete lower jaw, a femur, ribs, vertebrae and more! Tom and I were screaming, hugging and dancing, as mad as any Englishman in the midday sun!”

Johanson and Gray drove jubilantly back to their camp, their Land Rover’s horn blaring. Beer was chilled in the Awash River and grilled goat was served to celebrate their discovery – which was a sensational discovery anyway. A total of 47 bones from a single, ancient hominin (the term used to define humans and all our extinct bipedal relatives) were eventually discovered at the site by Johanson and Gray.

The fragments they collected represented about 40% of a complete skeleton, and later dating has shown that these remains are about 3.2 million years old. At the time, it was the oldest hominid creature ever unearthed by fossil hunters, and she was named Lucy.

Fifty years later, Johanson and Gray’s discovery remains one of the most remarkable breakthroughs ever made in human paleontology. The pelvis led scientists to conclude that it belonged to a woman, while her short legs suggested she was only about four feet tall. This discovery was followed by other similar finds, some in Ethiopia and some in Tanzania, and in 1978 Johanson—working with a colleague, Tim White—announced that these bones, including Lucy’s, all came from a single, previously unknown hominin species that they called Australopithecus afarensis: the southern monkey from afar.

Johanson and White placed afarensis at the base of a family tree that led to more recent species, such as Homo erectus and later Neanderthals and Homo sapiens. From this perspective, Lucy was the mother of humanity.

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

“Humans have three important characteristics: our ability to walk upright, our ability to make tools and our large brains,” says Stringer. “But a crucial question is: which of these traits came first in our evolution? What was the first step that led our ancestors to take a path that ultimately led to the appearance of… Homo sapiens?”

In The Descent of man, Darwin argued that the three human traits – bipedalism, tool making and large brains – evolved simultaneously, with development in one stimulating the other to evolve further. On that basis, brain enlargement would have been part of human evolution from the beginning. Then came Lucy’s discovery.

“Lucy showed that this idea was simply not true,” says Stringer. “Her skeleton showed that our ancestors walked on two feet long before their brains grew big.”

This point is supported by Zeresenay Alemseged, a paleoanthropologist at the University of Chicago. “Lucy showed that a big brain was not the sine qua non of being a member of the human lineage,” he says.

It’s an intriguing observation, and it raises important questions. Why did our ancestors walk on two legs in the first place? What evolutionary advantages did bipedalism provide?

Many answers have been suggested over the years. Ape-men would have walked on two legs and had free arms to pick fruit from low branches and could also carry food and babies. Standing upright, they would have appeared larger and more intimidating, while reducing the amount of bright African sunlight that beat down on their backs.

These are all thought-provoking suggestions, although the most likely reason was more prosaic, Alemseged argues. “If you walk on two legs instead of four, you save energy. It’s that simple. You burn fewer calories—and remember, our early ancestors didn’t have as much trouble losing weight as we do now. They had to get all the energy they could get and use it with maximum efficiency. Walking on two legs helped them do that.”

People today are paying for that transition to an upright gait – in terms of back pain and other skeletal problems that arise later in life. On the other hand, we reaped the rewards in terms of the expansion of our brains that eventually followed, in the wake of our adoption of bipedalism.

Lucy’s discovery posted afarensis the core of the story of human evolution. However, since its presence was first revealed at Hadar, many fossils of other, even older hominids have been found. These include Australopithecus anamensiswho – four million years ago – strolled through the terrain that is now in Kenya and Ethiopia, and Ardipithecus ramiduswho lived about 4.5 million years ago in a similar part of Africa. Importantly, these early ape-men also have anatomies that suggest they were bipedal.

So could it be possible that one of these species – and not afarensis – was the true origin of the lineage that led to Homo sapiens? Lucy’s relatives could have been just a branch of that family tree, and not a direct link to modern humans. In other words, was Lucy just humanity’s great aunt, not its mother? Some scientists believe that could be the case. Alemseged, however, has his doubts.

“These early hominins probably walked upright for a while, but many probably spent most of their lives in trees. Lucy and her afarensis relatives, on the other hand, spent a lot of time walking upright. They were crucial in the transformation of our genus into one that focused on upright posture.”

With Lucy our lineage reached the stage where upright walking became normal. We became obligatory bipeds, the defining characteristic of the lineage that eventually Homo sapiens.

Alemseged’s own contribution to this field was his discovery, on December 10, 2000, of Selam, the nearly complete fossil skull and parts of the skeleton of a child of Australopithecus afarensis. It is sometimes referred to as “Dikika child” or “Lucy’s child”, although the latter attribution is a misnomer, as the skull has been dated at 3.3 million years old and is therefore over 100,000 years older than Lucy.

“We have now found afarensis in Tanzania, Chad, Kenya and Ethiopia, and we know that Lucy and her relatives must have lived in these parts of Africa for almost a million years,” Alemseged added. “That antiquity and extensive geographic distribution convince me that this is the most likely candidate that gave rise to the many species of the genus Homo and ultimately to our own species. Homo sapiens.”

Lucy’s remains are now housed at the National Museum of Ethiopia in Addis Ababa, where Alemseged – who was born in Ethiopia – made headlines in 2015 when he was present to show Lucy to Barack Obama during the president’s state visit . She is the forerunner of all people today, he told Obama. “Everyone, even Donald Trump.”

Other scientists are more cautious about Lucy’s exact relationship to humans today. “The problem is that we only have 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 points out.

“In the former area there are lakes, rivers and sediments in which it is relatively easy to find fossils, while in South Africa there are many caves where early hominins became fossilized. That gives you a very biased view of hominin evolution in Africa. We don’t know what happened elsewhere on the continent,” Stringer added. “It’s a bit like the drunk man who looks at night for keys he’s dropped and only looks where there are street lights – because those are the only places he can see. Currently there is a shortage of places to find [fossil remains in Africa] and from places where people have actually looked, and that limits the evidence we can gather about exactly how the human lineage evolved millions of years ago.’

Nevertheless, it is clear that Lucy could have played an important role in developing our understanding of our own species – although her naming was rather haphazard, as Johanson admitted in recollections of the heady days that followed her discovery in Hadar. “Surely such a noble little fossil lady deserved a name, we all thought, and one evening as we were listening to Beatles songs, someone said, ‘Why don’t we name her after Lucy? You know, after Lucy in the sky with diamonds.” So she became Lucy.”

However, it could very easily have been a completely different name, as Caitlin Schrein has noted NatureThe Beatles song had been recorded seven years earlier. And if Johanson and his colleagues had been more up-to-date in their choice of pop music, or had had better access to records, they probably would have played more contemporary songs. Songs might even include some hits from 1974—like John Denver’s Annie’s Song or Elton John’s Bennie and the Jets. If they had been listening to these songs, the world’s most famous fossil skeleton would have had a different name.

However, the name may not be relevant. “The crucial point is that she was a great pioneer in highlighting early human evolution,” says Stringer.