The 3.2-million-year-old fossilized remains of Lucy, the most intact human ancestor ever discovered, began a six-year tour of U.S. museums last Friday. The scientific community has expressed concern about shipping and exhibiting such a precious and delicate specimen, and several prominent American museums have refused to display her. Given that many museums around the world have nearly identical plaster casts of Lucy, how important is the original fossil?
Very important. Although fossil replicas can be so similar to the original that even paleontologists have trouble telling them apart, such copies are of limited use for research. That’s because casts replicate only the outside structure of a fossil. Other information lies within the fossilized bones, and can be accessed via high-resolution CT (computed tomography). These scans can examine the inside of a fossil to determine, for example, how stress was imposed on the spongy internal structure of Lucy’s femur during her lifetime. Such information could help settle a debate about whether Lucy spent more time in trees or on the ground.
Although Lucy is too old and heavily mineralized to have any preserved DNA, traces of other chemicals in her fossilized bones may contain clues about what she ate and where she lived. Stable isotope analysis, which compares the ratios of different naturally occurring forms of chemical elements, could tell us about Lucy’s diet by looking for elements that are characteristic of certain plants. This would require cutting out and grinding up a tiny piece of the original fossil, and has not yet been attempted with Lucy.
Scientists can also directly measure the age of fossils that have retained enough of their original chemistry. Unfortunately, Lucy’s remains have almost entirely turned to stone, so this kind of analysis would not be possible for her. There’s always the chance that future technological advances could allow researchers to glean more information, such as direct dates, from Lucy’s existing chemistry, assuming that she’s still around and in good condition.
You can’t rely on bone-length measurements taken from a cast, either, since the replicas tend to deteriorate or deform faster than original fossil material. Casts made from plaster or plastic—such as most casts of Lucy—often become misshapen in unpredictable ways, especially when they are repeatedly handled or moved. The problem becomes worse when new casts are made from old casts, since a copy of a copy is less likely to be accurate.
History also reminds us of the value of access to original fossils. In 1912, Charles Dawson and Arthur Smith Woodward presented the remains of a human ancestor they called Eoanthropus dawsoni, or “Piltdown Man.” The find altered paleontologists’ view of human evolution for 40 years, until it was revealed that the “fossil” was actually a fake—a human skull had been combined with the jaw of an orangutan. The forgery was not exposed until 1953, in part because many paleontologists were allowed to carefully examine only casts but not the original “fossils,” which contained clues about the subterfuge.
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Explainer thanks Mark Goodwin of the University of California Museum of Paleontology, Donald Johanson of the Institute of Human Origins, John Kappelman of the University of Texas at Austin, and Anne Molineux of the Texas Memorial Museum.