Humans and their oral bacteria evolved from a common African ancestor
From the press release:
Researchers have found the first oral bacterial evidence supporting the dispersal of modern Homo sapiens out of Africa to Asia.
The team discovered that Streptoccocus mutans, a bacterium associated with dental caries, has evolved along with its human hosts in a clear line that can be traced back to a single common ancestor who lived in Africa between 100,000 and 200,000 years ago.
S. mutans is transmitted from mothers to infants, and first appears in an infant’s mouth at about two years of age. Caufield’s findings are reported in an article in the February issue of the Journal of Bacteriology.
In his analysis of the bacterium, Caufield used DNA fingerprints and other biomarkers that scientists have also employed to trace human evolution back to a single common African ancestor, known as "ancestral Eve."