The world’s most famous early human ancestor could walk upright like a modern-day human thanks to fully bendable knee joints, research suggests.

‘Lucy’ was from an extinct ape-like species that lived in Africa more than three million years ago.

She was dug up in Ethiopia in 1974, and at the time was the most complete known early human ancestor.

But only now have her lower limb muscles been fully digitally reconstructed, by researchers hoping to put an end to a decades-old debate among scientists regarding how she walked.

The results from a team at the University of Cambridge, published in the Royal Society Open Science journal, show Lucy could straighten her knee joints, stand upright, and walk on two legs like we do today.

But her legs were also found to be far bigger and more powerful than ours, allowing her to live in trees like apes, meaning she was equally well-equipped to adapt to life in open grasslands and dense forests alike.

The Cambridge scientists said the findings may help shed light on how physical movement has evolved in humans, “including those capabilities we have lost”.

How Lucy’s legs were reconstructed

A team led by Dr Ashleigh Wiseman made a 3D model of Lucy’s legs and pelvis muscles, with 36 in each leg.

The major muscles in her calves and thighs were more than twice as large as those in modern humans – the only remaining animal that can stand upright with straight knees.

Dr Wiseman, of Cambridge’s McDonald Institute for Archaeological Research, said: “Lucy’s ability to walk upright can only be known by reconstructing the path and space that a muscle occupies within the body.”

She added: “Lucy’s muscles suggest that she was as proficient at bipedalism as we are, while possibly also being at home in the trees.”

The history of Lucy

Lucy’s discovery in the 1970s was monumental because her skeleton was 40% complete, with 47 out of 207 bones intact.

It included parts of her arms, legs, spine, ribs, pelvis, lower jaw, and skull.

She was found to belong to the Australopithecus afarensis species, and given her name as the archaeologists who found her were listening to Lucy In The Sky With Diamonds by The Beatles at the time.

Researchers said she would have been a young adult when she died, just over one metre tall and under 30kg.

Since then, some experts have suggested she would have crouched and waddled like chimpanzees, while others believed she would have moved more like a human.