Lucy, the world's most famous fossil human ancestor, has gone digital in 3-D. A new high-resolution CT scan of the 3.2 million-year-old skeleton will provide scientists around the globe with information that may help settle debates about human evolution.

The virtual Lucy could prove invaluable to scientists by giving them their first glimpse inside her fossilized bones. The scans reveal microscopic details of the internal structure of Lucy’s bones and teeth that give clues to how she moved and ate.

“These scans will ensure that future generations are familiar with Lucy,” said Jara Mariam, director general of Ethiopia’s Authority for Research and Conservation of Cultural Heritage, “and will know of Ethiopia’s central contribution to the study of human evolution. A virtual Lucy will be able to visit every classroom on the planet.”

Several versions of the virtual Lucy will eventually be available to the public, according to paleoanthropologist John Kappelman of the University of Texas. A website with a basic version will allow students to look at Lucy and compare her skeleton with those of modern humans and apes, while researchers will be able to access high-resolution files. Lucy's bones, discovered in Ethiopia in 1974, represent the most complete remains of any adult human ancestor that walked on two feet. The prized fossil—currently on display at the Pacific Science Center in Seattle, Washington—sparked a controversy in 2007 when it was shipped to the United States from Ethiopia, because of concerns that it could be damaged. Now that Lucy has been digitally archived, scientists and students will be able to harmlessly examine the bones using tools available on the web.

Medical CAT scans like those done in hospitals show a cross-section of a patient’s body with 1-2 mm resolution. But because Lucy isn't a living patient, much higher-energy X-rays can be used. The computed tomography, or CT, scans done on Lucy reveal internal details on the order of 5-50 microns — less than the width of a human hair. That level of detail could yield unprecedented insight into our ancestors.

Pre-digital Lucy has already clarified key issues in the study of human evolution. Previous examinations revealed that our ancestors started walking on two feet before they developed large brains. The shape of her pelvis, feet, knees, and hip joints are all indicators that Lucy walked upright despite having a brain about the size of a chimpanzee. But many questions remain.

Although there is little doubt that Lucy’s species, Australopithecus afarensis, walked on two feet, it is less clear whether she and her kin also spent much time in the trees. Certain features of her skeleton — curved fingers and toes, the orientation of the shoulder joint, and relatively long arms — suggest at least a partially arboreal lifestyle. However, other experts contend that these features are evolutionary holdovers from tree-dwelling ancestors.

The question of whether Lucy’s species actually climbed trees or just inherited traits associated with tree-climbers is a long-standing debate among paleoanthropologists that the CT scans may help resolve.

“If we can compare the cross-sectional structural features of the limb bones we should be able to answer this question definitively,” said anthropologist Christopher Ruff of Johns Hopkins University.

Because bones get reinforced when they are extensively used (a right-handed tennis player will have thicker bones in the right arm than the left) researchers can compare Lucy’s upper versus lower limbs to see which she used more often.

“Your bones respond to how you use them,” explained paleobiologist Brian Richmond of George Washington University. “We know that spongy bone is especially sensitive to changes in activity and exercise.”

By comparing the thickness and the distribution of spongy bone in Lucy’s arms versus her legs, the researchers hope to finally determine if she spent much time in trees. Because Lucy’s skeleton is so complete — nearly 40 percent of her remains were discovered — she is the only fossil of her species where such a test is possible, because comparing the arm bone of one individual with the leg bone of another could be misleading.

The scans were conducted at the University of Texas at Austin’s High Resolution X-Ray CT Facility, which has extensive experience with unique and valuable specimens including the brain case of Archaeopteryx and a Martian meteorite. Yet, because of her high profile status, having Lucy at the facility provided a new challenge.

“It’s the first national treasure we’ve ever scanned,” said geologist Richard Ketcham, director of the facility.

Only Alemu Admassu, the curator of Ethiopia’s National Museum, was allowed to actually touch the fossils during the scanning process. Careful inspections before and after the scans verified that Lucy was not damaged during the procedure.

Now that the delicate work of conducting the CT scans is complete, the tedious job of analyzing the vast amount of data will begin. The team of researchers will spend the next few months trying to extract as much information as possible from the virtual Lucy.

“In some ways,” Ketcham said, “scanning Lucy was the easy part."

– Scott Solomon for Wired.com

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Images: 1) Lucy element in scanner. Marsha Miller/UT Austin; 2) Frank White/Houston Museum of Natural Science. Video: Jessie Maisano/UTexas Austin.