Workers at a travertine factory near Denizli, Turkey, were startled recently when they sawed a block of the limestone for tiles and discovered part of a human skull. Now, it appears they unwittingly exposed fossilized remains of a long-sought species of human that lived 500,000 years ago, researchers say. Although only four skull fragments were found, the fossil also reveals the earliest case of tuberculosis.
The Middle East has long been an important crossroads for human travelers. "It's been clear for some time that earlier hominids must have dispersed into Europe from western Asia and/or Africa, and Turkey sits squarely on the likely route," says paleoanthropologist Philip Rightmire of Harvard University, who was not a member of the team. Paleontologists have spent decades prospecting in Turkey for remains of a direct human ancestor, Homo erectus, which was the first hominid to migrate out of Africa. Although scientists have uncovered fossils of H. erectus that lived 1.7 million years ago in nearby Georgia, they have found few fossils of humans in this region that are between 1.7 million and 120,000 years old.
After the factory manager contacted a researcher at the local university, he alerted the rest of the team, which included researchers in France, Germany, and the United States. They report in the current issue of the American Journal of Physical Anthropology that the find most closely resembles H. erectus. However, Rightmire says it could also be a member of H. heidelbergensis, a species found in Europe that is thought to be the direct ancestor of Neandertals.
Regardless of its identity, lead author John Kappelman of the University of Texas, Austin, says the skull bears scars that are a "dead ringer" for those created by the Leptomeningitis tuberculosa bacterium, which causes a form of tuberculosis (TB) that attacks the brain's membranes. The scars represent the earliest signs of the disease in humans, says Kappelman. Previously, the oldest evidence of TB came from Egyptian and Peruvian mummies that were several thousand years old.
TB's presence might also provide clues about what this early human looked like and how it adapted to new habitats. If the hominid was dark-skinned, for example, it might have had trouble getting enough vitamin D as it migrated north, because dark-skinned people absorb less of the sunlight needed to make vitamin D than do light-skinned people. And when humans have vitamin D deficiency, their immune systems can be less vigilant, perhaps making dark-skinned migrants out of Africa more vulnerable to diseases such as TB as they headed to less sunny climates, says Kappelman.
"This is a hugely important discovery," says paleoanthropologist Clark Larsen of Ohio State University, Columbus, because infectious disease may reveal new challenges facing early humans as they moved into temperate regions. Kappelman hopes that the rest of the skull will be located eventually. "There was bone in the other slab we don't have," he says. "Someone may find the lottery prize of H. erectus preserved in their tile countertop."