Lucy, an early human ancestor who walked upright on two legs—a milestone in human evolution—had speed and energy efficiency ...

Lucy lived in a wide range of habitats from northern Ethiopia to northern Kenya. Researchers now believe she wasn't the only australopithecine species there.

Australopithecus afarensis, an ancient human ancestor who lived around 3 million years ago, spent most of its time walking, instead of climbing trees like chimps.

3D polygonal model, guided by imaging scan data and muscle scarring, reconstructing the lower limb muscles of the Australopithecus afarensis fossil AL 288-1, aka "Lucy." Credit: Ashleigh Wiseman ...

More than three million years after her death, the early human ancestor known as Lucy is still divulging her secrets. In 2016, an autopsy indicated that the female Australopithecus afarensis ...

A. afarensis existed at an important period in hominin history, when our earliest relatives were adapting to a life centered on walking, rather than climbing trees.

A sculptor's rendering shows what Australopithecus afarensis looked like 3.2 million years ago. Dave Einsel/Getty Images. Editor’s Note: Sign up for CNN’s Wonder Theory science newsletter.

A sculptor's rendering of "Lucy," Australopithecus afarensis, at the Houston Museum of Natural Science on August 28, 2007. Dave Einsel / Getty Images About 3.2 million years ago, among the ...

When Au. afarensis was named as a new species in 1978, it was the earliest human ancestor ever documented, with an age range of 3.8 million to 3.0 million years ago.

A sculptor's rendering of the hominid Australopithecus afarensis in an exhibition that included the 3.2 million-year-old fossilized remains of "Lucy." (Image credit: Dave Einsel via Getty Images) ...

A 3D polygonal model, guided by imaging scan data and muscle scarring, reconstructing the lower limb muscles of the Australopithecus afarensis fossil AL 288-1, known as ‘Lucy’.

The rare fossil, representing 40% of a skeleton belonging to a female Australopithecus afarensis, was named “Lucy,” for the Beatles song “Lucy in the Sky With Diamonds.” ...