Ancient virus maps migration of our ancestors
WASHINGTON When humans arrived in North America about 30,000 years ago, they brought language, fire, flint tools and skin tents. They also brought something they didn't know they had a tiny microbe called the JC virus sequestered in their kidneys.
Their descendants have shucked off Stone Age technology. But the JC virus is still with them.
Researchers are using the virus to bolster the hypothesis that American Indians came from Eastern Asia on a bridge of land or ice across the Bering Strait.
The strain of the JC carried by Navajos is nearly identical to that borne by residents of Tokyo. It's somewhat different from the virus carried by the Chamorro, the aboriginal inhabitants of Guam, but different from the virus carried by West Africans, East Africans and Europeans.
The evidence suggests the Navajo and the Japanese are closely related, and are more distantly related to the Chamorro. All are descended from the same prehistoric population of East Asians.
None of these insights is especially new. Anthropologists reached them years ago from studies of genetics and the archaeological record. What's new is to have them confirmed by a virus.
The JC virus is something that seems unimaginable a microbe that travels so intimately, and so ubiquitously, with human beings that it's essentially indistinguishable from the people themselves.
Nearly everyone on Earth acquires the virus as a child, usually from a parent. It rarely causes disease. Most important, its genes are astoundingly resistant to mutation, a distinctly uncommon trait for a virus.
The virus was first isolated from a human being in 1971. (The name comes from the person's initials.) Only in the last few years, however, have scientists realized they can differentiate human populations from one another by examining the strains of virus they carry, and from that deduce their movement over thousands of years.
"One would have thought that the distinctions (between viruses) would have been hopelessly homogenized," said Gerald Stoner, a neurotoxicologist at the National Institutes of Health in Bethesda, Md., and a leading expert on the "ethnicity" of the JC viral strains. "The surprising thing is that they have not. No one would have ever predicted that they would characterize populations like they do."
Anthropologists have studied biological "markers" for ethnic groups for a long time. Blood types and enzyme variants were the first to be used, but they provided only crude information about the biological underpinnings of ethnicity. With the advent of new technologies, researchers turned to human DNA for determining the relatedness of human populations. The JC virus joins human DNA as a tool for tracing communities through the genetic variations that crop up both in migrant groups and in their "ancestral" populations.
Stoner and a former postdoctoral fellow at the National Institute of Neurological Disorders and Stroke, Hansjurgen Agostini, believe the JC virus may have been carried by humans since the dawn of the species. They have identified seven major types, and nearly 25 subtypes, distributed around the world.