Viruses are one of the most persistent and potent forces of evolution, writes Pranay Lal in his new book, Invisible Empire: The Natural History of Viruses. As SARS-CoV-2 has shown, a virus is a force to be feared. “Everything about viruses is extreme, including perhaps, the reactions they evoke,” says Lal as he profiles this abundant life form with the help of photographs, illustrations, anecdotes and paintings. An excerpt from the book:
Much as we baulk at the idea, we are not unique. The human species, like all other living things, is an amalgam of creatures pieced together, gene by gene, and passed down by different life forms over deep time. Our genes were handed down to us from our ancestral ape, monkey, pig, shrew, gecko, fish, worm, grass, moss and bacterium, with several other creatures in between. Without genetic mutations, there would be no humans or, for that matter, any other life form that we see around us. These mutations — tiny errors in replicating the genetic code — occur randomly each time a cell (or virus) makes copies of itself, thereby becoming the starting point for an unexpected evolutionary journey. A very tiny number of mutations successfully create variation in a population. Natural selection then amplifies traits and creates variants which eventually can evolve into distinct species. These changes could be anything that confers an ability to thrive better in an evolving environment — blending a chameleon more effectively into a forest that is drying up; extending the necks of okapis and gerenuks so they can more easily nibble on the overhanging foliage of tall trees; or simply helping microbes evade a strong immune response and allowing them to attach themselves to a cell.
Viruses together with other microbes speed up the gene exchange between similar and often unrelated life forms. From a virus’s perspective, all living creatures are genetic Frankenstein’s monsters that they have stitched together. Nearly 8% of our genes, for instance, are uniquely viral in origin, and despite thousands and millions of years of adding, editing and deleting genes, we remain genetically similar in many ways. A virus is capable of crossing over into us to cause infection because some of our shared genes, proteins and common cellular components enable it to establish itself.
Take SARS-CoV-2, one of our most recent chance encounters. A few generations ago, a population of viruses acquired changes in their genes (and proteins) from an animal host which provided them with the ability to infect humans. The virus binds to a protein receptor, ACE2 (or Angiotensin-converting enzyme 2; angiotensin is a protein hormone that causes blood vessels to become narrower and is vital for maintaining blood pressure and fluid balance in the body), which it recognises in us. ACE2 is found in several mammals, and in us they are primarily present in our lungs and guts. When virologists teased open the RNA of SARS-CoV-2, they found that it carried genes that are found in a variety of animals – in other viruses, bacteria, slugs, small mammals, and perhaps unsurprisingly, therefore, nearly 94% of its genes are found in humans too. But a handful of its genes are completely unique to it and their functions are yet unknown. This makes it difficult to predict how SARS-CoV-2 will behave once it enters our bodies.
Our technological progress, our ability to acquire instant (albeit often ephemeral) gratification, has lulled us into believing that we possess enough power to subdue and manipulate nature. We choose which relationships we want to foster and which we will cull and sever, and try to make nature serve us selectively and indefinitely. This kind of brinkmanship makes us feel that we can control nature, but as we have been slow to realise, this control is delusional. It is time we stopped looking at nature as a pliable variable or as an entity that impedes ‘progress’, or a tool of one-upmanship. I say this now because there are controversies about the origin of SARS-CoV-2 – did the virus jump from an animal to unsuspecting buyers in a wet market or did it leak from a lab? Was it designed as a bioweapon? For me, these questions are relevant only if we have the courage to take corrective action and hold institutions or governments accountable. Otherwise this is a futile blame game best left to politicians and diplomats. The origin of the virus could be significant for science if it helps us determine the virus’s lineage and identify its potential hosts which will help us plan future strategies.
Regardless of how it originated, SARS-CoV-2 reminds us that provoking nature beyond a point can lead to unimagined and irreversible consequences. Anyone who understands nature’s processes knows that soils, mud, detritus, mulch, sand, gravel, grit and rock are crucial pieces in the climate change story, as are the ocean currents, wind circulation, the shapes and size of land masses and, of course, life forms – especially microbes, the principal primary energy producers on Earth that regulate the bulk of Earth’s carbon-oxygen cycle. When all these small pieces come together, they power Earth’s engines. This engine is an enormous, planetary scale, biogeochemical reactor – but it starts from small things. Viruses cause a billion infections a second. They tinker and shuffle genes at great speed, creating possibilities of making new varieties of life. Like geological processes which create and shape diverse landscapes, viruses and microbes enable speciation and find ways to fit new entities within ecosystems that their predecessors have shaped. Each ecosystem — a tropical forest, a vast grassland, a small pool or even microbiomes within every individual creature — has been thousands and even millions of years in the making, and is constantly evolving.
Here to stay
Like any other pathogen that established itself as a persistent disease, SARS-CoV-2, too, was a chance occurrence. We enabled its crossover through destruction of habitats and trade in wildlife. And once the outbreak occurred, mass movements of people, weak and bigoted science, the fragmented response by agencies, a blunderbuss of regulations and distrust between states sustained the spread and evolution of the novel virus. For SARS-CoV-2, the pandemic is not just a one-off chance but an evolutionary moment. The effects of the pandemic will not wear off any time soon. The virus has triggered massive changes starting with our bodies and embracing the body politic and these will probably stay with us for a very long time. Perhaps forever.
Excerpted with permission from Penguin Random House India