It turns out that we may be less human than we thought. Scientists have found that non-human DNA lurks within us, left by viruses that first infected our ancestors hundreds of thousands of years ago.
In this latest study, the researchers looked at the entire genomes of people from around the world. This included people from Africa, where the ancestors of modern humans originated before traveling around the world. The scientists used sophisticated techniques in order to compare key areas of each person's genome to a "reference" human genome.
In this case, the researchers found 19 new pieces of non-human DNA that were left by viruses that infected our ancestors. In addition, one piece of newfound DNA contained an intact, full genetic code for an entire virus.
But how did this foreign DNA end up in humans in the first place? These viruses are called human endogenous retroviruses (HERVs). These ancient infectious viruses inserted a DNA-based copy of their RNA genetic material into our ancestors' genomes. They're actually part of the same type of virus that includes modern human immunodeficiency virus, which cause AIDS.
Over time, this virus-generated DNA was copied and handed down from generation to generation of humans. Eventually, it wound up in our DNA today. In fact, about 8 percent of our "human" DNA actually belongs to viruses.
The newly discovered, intact virus is only found on the X chromosome and is known as Xq21. It's only the second intact provirus to be found in human DNA.
"This one looks like it is capable of making infectious virus, which would be very exciting if true, as it would allow us to study a viral epidemic that took place long ago," John Coffin, one of the researchers, said. "This research provides important information necessary for understanding how retroviruses and humans have evolved together in relatively recent times."
The findings reveal a bit more about these viruses, and possibly show researchers a bit more about human evolution.
"This is a thrilling discovery," Julia Wildschutte, co-first author of the new study, said. "It will open up many doors to research."
The findings are published in the March 2016 journal Proceedings of the National Academy of Sciences.
