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March 17, 2011 Volume 32, No. 24

Lucy’s arches could change views of human evolution

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EVOLUTIONARY FINDING Carol Ward, professor of integrative anatomy, recently discovered that a 3.2 million-year-old predecessor to humans, known as "Lucy," had arches in its feet, proving that the animal walked upright all the time. The discovery could change scientists’ views of how humans have evolved.


3.2 million-year-old clues

Researchers at the University of Missouri and Arizona State University have found proof that foot arches existed in a predecessor to the human species that lived more than 3 million years ago. This discovery could change scientists’ views of human evolution.

Carol Ward, a researcher in the Department of Pathology and Anatomical Sciences at the MU School of Medicine, and William Kimbel and Donald Johanson, director and founding director of the Institute of Human Origins at Arizona State University, studied a 3.2 million-year-old fourth metatarsal of Australopithecus afarensis. A team from the Institute of Human Origins and National Museum of Ethiopia led by Kimbel discovered the fossil in Hadar, Ethiopia. The species is often referred to as “Lucy,” the nickname of the most complete fossil skeleton of the species to be discovered.

The foot bone suggests that these hominids had stiff, arched feet, similar to humans. Australopithecus afarensis had smaller brains and stronger jaws than humans, and scientists have known the animals walked upright on two feet. However, researchers have not known whether Lucy and her kin were more versatile creatures than humans and spent time climbing through the trees.  

“This affects much of what we know about them, from where they lived to what they ate and how they avoided predators,” said Ward, professor of integrative anatomy. “The development of arched feet was a fundamental shift toward the human condition, because it meant giving up the ability to use the big toe for grasping branches, signaling that our ancestors had finally abandoned life in the trees in favor of life on the ground.”

With human-like arches in its feet, Australopithecus afarensis was able to roam the countryside and leave the forest to forage for food when necessary. With its strong jaws, Australopithecus also could eat several types of food, including fruit, seeds, nuts and roots. Combining their strong jaws and their new skill of walking, Lucy and her relatives were able to live in open areas as well as wooded ones.

Australopithecus was a new kind of hominin, fundamentally different from an earlier species that was not committed to walking upright. That species, Ardipithecus ramidus, moved on all four feet or upright depending on the situation, and had powerful grasping feet.  

“Arches in the feet are a key component of human-like walking because they absorb shock and also provide a stiff platform so that we can push off from our feet and move forward,” Ward said. “Understanding that the arch appeared very early in our evolution shows that the unique structure of our feet is fundamental to human locomotion. If we can understand what we were designed to do and the natural selection that shaped the human skeleton, we can gain insight into how our skeletons work today.”

Kimbel said the ongoing work at Hadar is “producing rare parts of the skeleton that are absolutely critical for understanding how our species evolved.”

The study was recently published in Science, the journal of the American Association for the Advancement of Science.