A recent study published in Proceedings of the National Academy of Sciences shows that we are less human than we originally thought. In total, 19 new pieces of ancient viral DNA have been discovered in the human genome. And even more surprising, 2% of people contain the DNA of entire virus.
Retroviruses are what implant these extra DNA parts into our genome. Retroviruses infect the host cells, inserting a DNA-based replica of their own RNA in the genome of their host. The most common example of a retrovirus is HIV.
Known as HERVs or human endogenous retroviruses, these fragments of DNA have been copied and passed down, generation to generation for hundreds of thousands of years.
This new study was seeking previously unknown HERVs. They examined the genome of 2,500 people from all over the world and compared it to a “reference” type; or a digitized genetic sequence that was assembled by scientists to act as a representative sample of the human genome.
They found 19 new HERVs to add to the 17 already identified by other studies. One of these HERVs was found completely intact in 50 of the study subjects. A completely intact virus DNA is known as “provirus” and is only the second known to exist in humans. Proviruses could potentially replicate and start working like a virus, where the fragments pieces can not.
“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,” said the study’s coordinating author John Coffin, a virologist at the Tufts University School of Medicine, in a statement.
HERVs have served a useful evolutionary purpose. One HERV in particular has created a protective layer during pregnancy that stops toxins from the mother’s blood from entering the fetus. Since these HERVs have been an integral part of our human biology, finding them could result in medical breakthroughs.
This study has added another bunch to the pack – as well as revealing how “alien” we truly are. Eight percent of your DNA is alien, in that it’s made up of non-human, viral fragments. In fact, viral fragments are often hiding within the genome of anything on Earth that has a jaw and a spinal cord, which is a remarkable reminder of how they’ve shaped evolution for hundreds of millions of years.