A Neanderthal rib fragment provides conclusive evidence that the ancient hominins were susceptible to a benign bone tumor of modern humans.

In the mid-1980s, University of Pennsylvania graduate student Janet Monge and Penn colleague Morrie Kricun undertook a project to X-ray the 900 or so bones of the Krapina collection—Neanderthal remains originally unearthed at the turn of the 20th century a few dozen kilometers north of Zagreb in the former Yugoslavia (now Croatia). For two weeks, the team loaded dozens of specimens at a time into individual, form-fitting Styrofoam holders and shuttled them from the Croatian Natural History Museum to the veterinary school in Zagreb, which had made its X-ray equipment available to the researchers. Their goal was to publish a radiographic atlas of the entire collection.

For the most part, the process went smoothly, but there was one X-ray—of an unusually thin and light rib fragment—that appeared “burned out” in the radiographic image, Monge says. Despite using the same amount of radiation as they had for similar specimens, “all of the radiation [went] through the object, rather than being absorbed or reflected by the object, so rather than looking like a bone with white or gray and black sections, it appeared completely black,” she explains. “Immediately we knew something was up with the little fragment.”

The researchers were hopeful that they might be able to lighten the image or increase the contrast to make out some of the bone’s detail, but upon returning to Penn and digitizing the X-rays, Monge had no luck. “I realized that basically there was no detail on it at all, no matter how you manipulated it,” she recalls.

NEANDERTUMOR: The diseased Neanderthal rib (a) shows clear deterioration of the lattice-like structure inside the bone, while in a modern, healthy bone (b) that structure is intact. Image courtesy of PLOS ONE, DOI:10.1371/journal.pone.0064539.g001

Unfortunately, other research projects—as well as ongoing political turmoil in the region—kept the team from returning to Zagreb for more than a decade. Finally, in the late 1990s, with the atlas still unpublished, another Penn collaborator, Alan Mann, now at Princeton University, drove to Croatia from France, where he ran a field school for students excavating Neanderthal sites, to get a better X-ray of the rib fragment. He brought the film back to Monge—by that time a curator at the Penn Museum of Archaeology and Anthropology—who digitized it as she had the rest of the collection. The quality still wasn’t great, but it was good enough, they decided, and they published The Krapina Hominids: A Radiographic Atlas of the Skeletal Collection in 1999.

But Kricun, a bone radiologist, couldn’t get that rib fragment out of his mind. Studying the image they had just published, Kricun noted that the normally hard exterior, called the cortex, was very thin, and that the bone lacked almost all of the spongy interior—which explained why the radiation levels used for similar specimens turned out to be way too high for this hollowed-out fragment. He suspected the malformed bone was evidence of a fibrous dysplasia, a rare type of benign tumor occasionally found in the ribs and other bones of modern humans.

To confirm his suspicions, however, the team needed more information. So last year, the researchers asked colleagues at the University Hospital in Zagreb to take more X-rays, and persuaded the Croatian Natural History Museum’s Davorka Radov?i? to conduct micro-CT scans. “We wanted to have good color photos of it,” says collaborator David Frayer, a paleoanthropologist at the University of Kansas. The CT scans involved “more than 1,000 cuts in the imaging, so that it’s a very accurate, detailed account of what the cavity looks like [that] you can’t really get from a 2-D X-ray.”

Sure enough, the results confirmed that the individual, likely an older teen or young adult, had the oldest documented case of fibrous dysplasia by more than 100,000 years. “I’ve never seen anything like this and I’ve looked at lots of skeletons,” says Frayer, who has worked with the Krapina collection for more than 2 decades.

Human paleontologist Fred Smith of Illinois State University in Normal says that, while he is not surprised by the existence of a Neanderthal tumor of this sort, the finding “underscores in some ways the fact that these Neanderthals basically [had] the same kind of biology that we have and they [were] subject to the same kind of growth and developmental processes, even abnormal.”

“It is important to know that the very same kind of change associated with this tumor is something that we share with Neanderthals,” agrees Monge. “That has a very, very deep history within the human lineage and very much ties us—in terms of disease pathological processes—to Neanderthals.”

- This article was originally published in our sister publication, The Scientist, on Sept. 1