The body's DNA isn't exactly human, at least for 19 new pieces of DNA left by prehistoric viruses. The human DNA contains remnants of infectious viruses that first infected our ancestors hundreds of thousands of years ago, scientists found.

The body's DNA contains traces of infectious viruses that have lurked in ancient humans. These pathogens, called endogenous retroviruses (ERVs), were passed down from one generation to another. Good thing, they mutated in a way that disabled their ability to cause infection, until they eventually became part of the human DNA.

A team of scientists and geneticists from Tufts University and the University of Michigan Medical School, however, found 19 new pieces of DNA left by viruses, resting dormant between our own genes. Published in the journal Proceedings of the National Academy of Sciences, the scientists described their discovery of one stretch of newfound DNA in about 50 of the 2,500 people examined. This contains an intact and full genetic make-up of an entire virus.

It is still unclear if the virus can replicate but previous studies have shown that ancient viruses in the DNA can affect human carriers. In recent years, there are 17 other pieces of virus DNA found in the human genome and the study wants to focus on searching for the entire human genome.

They looked at the genome or entire span of DNA from people across the globe focusing more on those living in Africa, where ancient people came from before spreading throughout the world.

"Many studies have tried to link these endogenous viral elements to cancer and other diseases, but a major difficulty has been that we haven't actually found all of them yet," said Zachary Williams, a doctoral student at the Sackler School of Graduate Biomedical Sciences at Tufts University.

The discovery sheds light on human endogenous retroviruses, or HERVs. The human DNA contains all characteristics humans have, including the color of the eyes or hair and some medical conditions. Somehow, viruses made it to the human DNA and through the years, it has been replicated and passed down and that has led to what human DNAs are today.

Having these viruses in the human DNA isn't all that bad because somehow, the body has adopted HERV sequences to impose beneficial effects like helping pregnant women build a cell layer around a developing baby to protect it from the toxins and antibodies in the mother's blood.

The new discovered HERVs, is part of a family called HERV-K while the entire viral genome is now called Xq21 since it was on the X chromosome.

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