In Paris, France in 2006, Thierry Heidmann reconstructed an ancient virus in a microscopic, real-life version of Jurassic Park. Yet, his goal was not to recreate a movie in his lab for his own curiosity. He found that his virus, which he dubbed Phoenix, incorporated itself into the genome of its animal cell host. After the completion of the Human Genome Project in 2003, DNA sequencing revealed that an astonishing 8% of our genome is comprised of viral DNA fragments – repressed in today’s humans – a glimpse into generations upon generations of evolutionary history.
Darwin had likely noticed the evolutionary relationship between human and chimpanzees for much of his life. Yet, how could he have foreseen a relationship so intricately woven into the human genome as to completely go against the stigma of “infection”? How could he have predicted such an important symbiosis between host and parasite DNA?
Darwin’s own theory, in a sense, is evolving. Modern equipment and scientific advances have brought with them a coalescence of health science, genetics, and ancient history. Admittedly, even though I live in the 21st century and recognize the potential of DNA, I could never have imagined that viruses positively shaped our history. Although mutations in the human genome must have already been present, as viruses evolved and posed new threats to humans, a change in the environment, that is, a component of natural selection, would favor serendipitous mutations in a fortunate cell, and with it, our genome could change dramatically. Immunity is just one of many possible mutations that can be selected for in the presence of a virus in the environment. Thus, in the words of Indian evolutionary geneticist Harmit Malik, “We have been in an evolutionary arms race with viruses for at least one hundred million years…..One party is winning, the other losing, all the time. That’s Evolution. It’s the world’s definitive game of cat and mouse. Viruses evolve, the host adapts, proteins change, viruses evade them. It never ends.”
Despite this cyclic progression in which evolution is followed by counter-evolution (hence the “arms race”), by resurrecting of extinct viruses and causing interactions between these viruses and modern cells, biologists have recognized the big picture of millions of years of cell-virus interaction at the molecular level. This knowledge, made possible with scientific and technological advances, has formed the foundation for the next generations of scientists to apply biological reasoning to develop cures for some of the world’s most rapacious viruses, such as HIV. In Kinshasa, Democratic Republic of the Congo, in 1959, the virus was discovered in the blood of a man who, after some contact with a chimpanzee (Pan troglodytes), likely received the virus, which had previously been the simian immunodeficiency virus (SIV) prior to a mutation that altered its receptor proteins. The virus has ravaged much of Africa and the United States, and has developed into a pandemic.
Around five million years ago, the lineages of humans and chimpanzees diverged. Prior to this division, the virus Pan troglodytes endogenous retrovirus (PtERV) spread across the chimpanzee population. The human version of the gene TRIM5α coded for a protein that resisted PtERV, whereas chimps remained susceptible. After recreating PtERV, biologists discovered this surprising idea: they deduced that once the human lineage diverged from apes, the human population was susceptible to another virus (HIV), to which the rhesus monkey, for example, had a resistance. Thus, evolution perpetuated molecular differences among newly diverged species.
I had always thought of viruses as an exclusively negative force. Viruses certainly have detrimental impacts on populations, as is seen in the spread of HIV/AIDS across the human population. Yet, these viruses have both spurred our evolution and provided us, with scientific innovation, valuable knowledge about the molecular biology of viral illnesses, marking the first steps towards developing potential cures and other therapies for even the most aggressive illnesses. Of course, it is imperative that viruses, ancient or modern, be controlled after their resurrection. However, within ethical principles, further research in virology and molecular biology could drive generation after generation of ambitious endeavors in combatting disease, making differences in the future that are already foreseeable now.