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The "out-of-Africa" theory states that all Homo sapiens once originated from the continent of Africa. Even though this theory is supported by many studies examining the human genome, not everyone is sold on the idea that humans migrated out of Africa around 150,000 to 200,000 years ago. However, a new study out of the University of Wisconsin, Madison found more evidence that support this theory. The researchers of this study examined strains of Herpes simplex virus type-1 (HSV-1) and found similar migratory patterns.

For this study, senior author, Curtis Brandt, professor of medical microbiology and Ophthalmology worked with Aaron Kolb and Cécile Ané. Together, the team decided to compare 31 strains of HSV-1 that were collected from North America, Europe, Africa and Asia. They decided to study HSV-1 because the virus is easy to collect, relatively mild and much easier to study when compared to the human genome. When the researchers compared the strains, they found that the strains were similar relative to the continent.

"The viral strains sort exactly as you would predict based on sequencing of human genomes. We found that all of the African isolates cluster together, all the virus from the Far East, Korea, Japan, China clustered together, all the viruses in Europe and America, with one exception, clustered together," Brandt said according to a news release from UW-Madison.

Despite the fact that the strains appeared to cluster in their respective regions, the researchers found evidence that the strains had migrated throughout the world. The team used high-capacity genetic sequencing and advanced bioinformatics to study the virus's genome. They were able to break down the genome into 26 parts. The parts were then organized into family trees so that the researchers could more accurately determine where they originated. The team found that certain strains from different parts of the world were connected. For example, they isolated one strain from Texas and found that it was very similar to the strains from Asia. Furthermore, the researchers found that the strains from Africa appeared to have the oldest roots, which suggest that the other strains might have migrated from Africa.

"What we found follows exactly what the anthropologists have told us, and the molecular geneticists who have analyzed the human genome have told us, about where humans originated and how they spread across the planet," Brandt said. He added that what they found "was clear support for the out-of-Africa hypothesis. Our results clearly support the anthropological data, and other genetic data, that explain how humans came from Africa into the Middle East and started to spread from there."

The study was published in PLOS ONE.