The Beginning

"One fossil discovery above all has transformed views of how we became human. But who was Lucy, and why is she so important to human evolution?

Lucy was discovered in 1974 by anthropologist Professor Donald Johanson and his student Tom Gray in a maze of ravines at Hadar in northern Ethiopia.

Johanson and Gray were out searching the scorched terrain for animal bones in the sand, ash and silt when they spotted a tiny fragment of arm bone.

Johanson and Gray named their fossil skeleton Lucy, after the Beatles song 'Lucy in the Sky with Diamonds'. Lucy may have looked something like this.

Discovery of a lifetime

Johanson immediately recognised it as belonging to a hominid. As they looked up the slope, they saw more bone fragments: ribs, vertebrae, thighbones and a partial jawbone.

They eventually unearthed 47 bones of a skeleton - nearly 40% of a hominid, or humanlike creature, that lived around 3.2 million years ago. Based on its small size, and pelvic shape, they concluded it was female and named it 'Lucy' after 'Lucy in the Sky with Diamonds', the Beatles song playing on the radio when Johanson and his team were celebrating the discovery back at camp.

An upright chimp

Like a chimpanzee, Lucy had a small brain, long, dangly arms, short legs and a cone-shaped thorax with a large belly. But the structure of her knee and pelvis show that she routinely walked upright on two legs, like us.

This form of locomotion, known as 'bipedalism', is the single most important difference between humans and apes, placing Lucy firmly within the human family.

"Bipedalism is the most distinctive, apparently earliest, defining characteristic of humans," says Johanson, now director of the Institute of Human Origins at Arizona State University.

Admired from Afar

Johanson named Lucy's species Australopithecus afarensis, which means 'southern ape of Afar', after the Ethiopian region where Hadar is located.

3.5 million years ago, Australopithecus afarensis foraged for fruit, nuts and seeds in a mixture of savannah and woodland. It may also have obtained animal protein from termites or birds' eggs.

In 1975, Michael Bush, one of Johanson's students, found the remains of more than 13 afarensis individuals buried together following a natural disaster - possibly a flash flood. The find yielded vital information about afarensis' social organisation.

"It is clearly a mixed sample of young and old, large and small - meaning several females and several males. It looks very much like the composition of afarensis groups was like what we see in chimpanzees," Johanson explains.