Oldest Human TB Case Found in 500,000-Year-Old Fossil
for National Geographic News
|December 7, 2007|
Tuberculosis may have infected human ancestors much earlier than previously thought, according to scientists who have discovered traces of the disease in a hominin fossil about 500,000 years old.
Researchers say the findings could provide a better understanding of the roles of climate, health, and evolution in ancient human migration.
The fossilized Homo erectus, an extinct branch of early human ancestors, was discovered in a block of travertine rock mined from a quarry near Kocabas in western Turkey.
Based on the shape of the skull and large ridges of the brow, scientists think the remains belong to a male between 15 and 40 years of age. But they also found something else.
"There were widespread little lesions on the inside of the skull," said John Kappelman, an anthropologist at the University of Texas, Austin.
"Those lesions are distinctive of a specific kind of tuberculosis that infects the meninges, or membranes that surround the brain," he added.
During such an infection, inflamed nodules within the membranes create pressure on the bone surface, leaving the lesions.
Kappelman's findings appear in today's issue of the American Journal of Physical Anthropology.
Vitamins and Skin Color
The findings offer insight into how vitamin D might have played a crucial role in early human migration.
Vitamin D is synthesized in the skin by exposure to sunlight. Since ultraviolet radiation penetrates only the top layers of skin, people with darker complexions produce less of the vitamin, as the pigment in their skin filters out the light.
Previous studies have suggested that humans migrating north developed a lighter skin complexion as an adaptive response to maintain their vitamin D levels when exposed to less sunlight.
Last year scientists found how vitamin D produced in the skin regulates the immune system and triggers certain reactions that kill the germs that cause tuberculosis.
Kappelman thinks that theory could not only explain how the Kocabas male contracted tuberculosis but may also shed light on human migration.
"We found from medical literature that [modern] people who have migrated from southern latitudes—and are more likely to have a darker skin color—to more northern latitudes show a higher incidence of tuberculosis, and that appears to be linked to a vitamin D deficiency," Kappelman said.
After a presumably dark-skinned population of Homo erectus had migrated north, his team's theory holds, the young male in Kocabas was unable to generate enough vitamin D from the reduced sunlight, and a tuberculosis infection proved fatal.
Spencer Wells is a National Geographic Explorer-in-Residence who was not involved in the current study. (National Geographic News is a division of the National Geographic Society.)
Wells said the findings suggest that tuberculosis "might have been the scourge of the hominid lineage for much longer than we suspected."
But he added that he is not convinced darker skin predisposes people to tuberculosis.
Present-day immigrant communities have higher rates of infection due to their lower socioeconomic status and more cramped housing, he said.
Moreover, Homo erectus fossils as old as 1.8 million years have been excavated from Dmanisi, Georgia, he added.
(Read related story: "Odd Fossil Skeletons Show Both Apelike and Human Traits" [September 19, 2007].)
"Compared to this [Turkish] specimen, which is about 500,000 years old, [the Georgian specimens] had 1.3 million years to evolve lighter skin.
"Certainly they would have done it if it was a major selective pressure," said Wells, who also heads National Geographic's Genographic Project.
Kappelman said such an adaptation may well have occurred if the population had stayed north. But the migrants were likely unable to remain due to the severity of cold glacial stages at the time, he said.
"We think there were probably multiple population migrations from southern latitudes to the north, but those early populations were pushed back south during times of extreme climate," he said.
Colin Groves, an anthropologist at Australian National University in Canberra, agreed.
"They were not permanent residents, and their range contracted back into Africa when the ice sheets swept south into Europe," he said.
Each time the climate improved, a fresh population would migrate north, readapting to the conditions, he added.
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