Viruses have been long thought of as only detrimental to humans, due to the diseases they cause. But what would happen if viruses have beneficial, and even crucial effects on humans and the general theory of evolution? This question was applied to retroviruses, as they are the only viruses capable of inserting their genetic material into our germ cells, thus affecting our offspring. After having mapped out the human genome, scientists discovered that retrovirus DNA composes 8 percent of our genome, and thus became interested in discovering how viruses could have affected our genome so profoundly. To answer this, scientists had to piece together viruses from genetic information in our DNA, to great success. Thierry Heidmann was responsible for “reviving” such a virus, and this led to him saying that “What is remarkable here is that endogenous retroviruses are two things at once: genes and viruses.” Surprising, to be sure, and Heidmann and other scientists suggest that without the contribution of retroviruses to our genomes, we perhaps could not have existed.
Such a discovery is remarkable, and so, scientists were determined to see if this information could be used to further prove Darwin’s theory of evolution. This meant that if scientists could find traces of the same viruses in different species of organisms, then this would imply common ancestry between unrelated species of organisms. This would have certainly surprised Darwin, since scientists could conclude that humans evolved from both apes and viruses. To be more specific, since the same retroviral DNA could be found in both apes and humans, the only way that this could happen is by inheriting it from a common ancestor.
Once this theory was accepted, then came the task to find out how retroviruses could help shape us as a species. Since retroviruses were still a threat when they were active, those individuals with ways to cope with them passed their coping mechanism to their offspring, and thus, as time passed by, individuals inherited better coping mechanisms and made the species as a whole more fit. One application of retrovirus DNA affecting the way that humans to evolve is that there is genetic information that in retroviruses would help them to attach to their hosts. When this genetic information was incorporated into an ancestor’s genome, it could have possibly allowed mammals to move from egg-laying to live births, due to the ability of cells to fuse together to create placentas, a characteristic found in most mammals nowadays.
Due to further genetic work, scientists were able to determine that when we evolved resistances to some viruses, we opened the door to others, such as in the example between HIV and PtERV.
Eventually, scientists then thought that certain retroviruses have certainly shaped our evolutionary history, but then again, could all retroviruses do the same? It was initially inferenced that this was not possible, as lentiviruses like HIV work slowly and would not infect germ cells. However, scientists then discovered a lentivirus, dubbed RELIK, had incorporated its genetic material in a species of rabbit, shattering the preconception that lentiviruses could never become endogenous. Because of this, scientists were hopeful that this information could be used to hasten the destruction of HIV worldwide.
In the end, seeing as retroviruses forced species to adapt to it, and that such adaptations inadvertently led to different ways in which the species interacted with the environment, one could conclude that the retroviruses have certainly been a driving force in evolution. Such a conclusion is amazing since it could mean that so as long as we continue to adapt to viruses, the viruses then become an agent of change, thus leading to further evolution.