The viral DNA in our genomes comes from HERVs, which stands for human endogenous retroviruses. At some point in our history, these viruses inserted DNA copies of their genetic material into a sperm or an egg cell, causing humans to be born with the viral DNA in their genes. Many generations later, humans now have several times more viral genes than they do human protein-coding genes. (Only a fraction of our genes actually code for proteins, remember.) Recently, scientists found 19 new pieces of viral DNA in human genomes, including a complete viral genome as opposed to just a piece of one. As we continue to examine our genetic makeup, we may learn that we're less and less human.