What Percent Virus Are You?

The more scientists look for viruses, the clearer it becomes that they exist nearly everywhere — a drop1 of surface seawater typically contains about 10 million of them. Viruses are found across the globe — on land, in oceans, and in a variety of host organisms, from bacteria to plants and animals. And that includes humans, down to our genetic building blocks.

Since viruses cannot replicate on their own, they use the cells of the organisms they infect to make new copies of themselves. One type of virus, retroviruses, inserts a DNA copy of its RNA sequence into the host cell’s genome upon infection. If the virus inserts into a reproductive cell and that cell goes on to produce an offspring, the viral DNA gets passed on from parent to child as part of the genome.2 At this point, the virus is locked in and is passed on from generation to generation. These are called endogenous retroviruses, or ERVs, and this can happen in any type of organism that viruses infect, including humans.

So yes, that means your genome is part virus. More than 100,000 sequences in the human genome3 originated this way. Scientists have recognized the presence of viral DNA in the human genome for decades, but it wasn’t until after the human genome was sequenced, or mapped, in 2003 that they could study just how much of our DNA comes from viruses. While the viral sequences in the human genome today originated from about 50 infection events in the distant past that were passed on as described above, the viral sequences were copied and reinserted hundreds, sometimes thousands, of times.

With advances in genome sequencing and computational tools to analyze genomic information, researchers are able to estimate that about 8 percent of the human genome is made of sequences that originated as invasive retroviruses. To put that number in perspective, genes4 make up about 1 percent to 1.5 percent of your genome.