However, though both sets of data indicate a period of relatively constant population size followed by a rapid increase, a closer look reveals that while human populations started to expand considerably about 50,000 years back, the viral population expanded only in the last few hundred years.
"Besides, there are several instances of one population group harboring a subtype typically associated with another group," she said. "For example one finds viruses from the Japanese and Korean subtype in the European subtype group--another incongruency."
If the virus had been strictly passed down from parent to child and had kept step with human migration, one would expect the various subtypes to group together geographically, she explains.
Shackelton added that if the co-evolution of the virus and human populations were as strict as previously thought one would not find so many differences in the family trees of the virus and humans.
Researchers also said that this study and others by the group suggest that DNA viruses may not have a slow rate of evolution as previously thought, and that the viruses like JCV might in fact be evolving twice as fast.
'"/>
Source:Penn State