Late in the year 1859, a man by the name of Charles Darwin published a work of scientific literature titled On the Origin of Species by Means of Natural Selection. In it, Darwin proposed a radical — at least for the 19th century — mechanism for evolution: natural selection. Darwin argued that based on selective pressures found in the environment, a population would evolve so that the traits of individuals best suited to withstand those selective pressures, and thus individuals capable of reproducing most successfully, would become more common. Evolution as Darwin understood it was entirely a result of selective pressures that encouraged an increase in the frequency of advantageous traits in a population, thereby altering it.
Darwin would have been surprised, however, to learn that evolution does not always occur as a result of environmental pressures acting upon organisms on a macro level. Viruses, which are generally considered to be among the selective pressures that mold human populations have played a role in shaping the human experience with much more intimacy: some of them have become a part of our DNA. For all intents and purposes, endogenous retroviruses — viruses that embedded themselves into our ancestors millions of years ago — play a huge role in making us who we are today. With the utmost certainty we can say that in line with Darwin’s proposal, viruses acted as Mother Nature’s henchmen, carving away at the human family tree to increase the frequency of some traits in our populations and decrease the frequency of others, but what Darwin could have never predicted is that they also changed humanity much more directly by embedding themselves into our genome.
The most shocking thing about reading Michael Specter’s Darwin’s Surprise was learning certain scientists believe that without pathogens, humans might have never developed a placenta. Without placentas, live births would likely not have been possible, and as live births hold great significance in determining mammalian success over other classes of animals, the importance of viruses in the evolution of modern humans was hammered home through this revelation. Generally, simply reading the word virus is sufficient to bring to mind horror stories of projectile vomiting, lesions, endless, bloody coughing, and a plethora of other unpleasant images. Thus it is surprising to consider that viruses may actually have had a significant contribution to the evolution of modern homo sapiens. Without viruses, placentas may not have existed and without placentas, the large brains central to human complexity may never have developed.
Darwin’s Surprise forced me to completely reevaluate my attitude toward viruses. From a humane perspective, viruses and the center-stage roles they play in devastating epidemics such as the recent ebola crisis and the ongoing battle against AIDS are entirely tragic and humanity would be better off without them. After reading Darwin’s Surprise, however, it is clear that despite the suffering they have caused, humanity may not have had the same level of evolutionary success without viruses, and it might be fair to say that I have even come to appreciate them for contributing positively to the human genome, even if they did so by inserting their own DNA into ours.
The question of whether or not science should revive dead viruses has no simple answer. On one hand, paleovirology can unlock answers to many of our evolutionary history’s mysteries. On the other hand, bringing back viruses that our species fought for generations to overcome does not seem like a particularly responsible idea, even if scientists can ensure that the virus can only reproduce once. As Michael Specter mentions in Darwin’s Surprise, retroviruses have infamously high rates of genetic mutations which make them particularly challenging adversaries for those trying to develop vaccines against them, so the possibility that retroviruses may be able to sidestep whatever mechanism scientists use to ensure singular reproduction will always remain. However, in the face of the threat humanity faces from antibiotic resistant bacteria, the value of knowledge to be gained from studying evolution through revived viruses may outweigh the risks of doing such experiments. I believe that only research facilities that are properly equipped to immediately quarantine themselves in the event of a mishap that might lead to public exposure to the viruses should be allowed to revive dead viruses.
Darwin’s Surprise is certainly a thought-provoking read that presents an entirely new perspective on viruses. I now acknowledge the importance of viruses in adding to our genome and shaping what it means to be human in a way that Charles Darwin could not have expected. Nevertheless, you won’t find me seeking exposure to any little viruses anytime soon.