When one thinks of the similarities between modern and ancient humans, one will probably think of the basic genetic material that determines our physical structure. However, what is not so obvious are the viruses that infected them yet remain in our genes. It is known that DNA containing these ancient viruses make up about eight percent of the human genome (Ancient Viruses). These viruses have previously been believed to be insignificant, however, recent research has disproved this theory.
The viruses that have been genetically passed down are known as retroviruses. Retroviruses spread by making copies of themselves through the production of RNA which contains instructions for its DNA and replication. This reproduction process, called transcription, is similar to that which is done in the nucleus of eukaryotic cells. However, in this case, the synthesized DNA is then placed in the DNA of the cell it occupies. With that in mind, For the genes containing these viruses (or any gene) to be activated, they must contain specialized RNA with the information for its reproduction and it must be revealed by a protein called the transcription factor.
Using data from the Genotype-Tissue and Expression project, scientists Aidan Burn, Farrah Roy, Michael Freeman, and John M. Coffin searched for these active virus genomes in healthy tissue. They specifically sought out HML-2 which is a relatively new virus. They also looked for the RNA which would indicate its activation. This virus was found in all of the tissue they examined and they found the highest activity of it in the cerebellum.
Though they were once harmful to humans, these viruses found within healthy cells and tissues no longer serve as functioning viruses. They are now known as Endogenous Retroviruses (ERV). They cannot infect, but rather they serve us in our immune system. Their activation has been shown to have a vital role in embryonic development and aid in the detection of cancer.
I found the origination of ERV in human genomes to be similar to that of mitochondria and chloroplasts’ origin in eukaryotic cells. It is likely that mitochondria and Chloroplasts were engulfed by bacteria cells and are now able to carry out their functions (reproduction) within them while also benefiting the cell (providing it with ATP). Similarly, at some point during human evolution, the virus entered humans and was then able to utilize its environment (the host cell) to reproduce. I would also describe the relationship between ERV and modern-day humans as symbiotic due to the recent research which has revealed their benefits.