10 things you need to know about viruses

From global pandemics to drivers of evolution – how viruses shape the journey of life on Earth

With the coronavirus pandemic causing misery around the world, it’s more important than ever to stay positive and remember the fact that humanity has survived greater challenges throughout the course of its 200,000-year journey. And what better place to look than the realm of science? In today’s post, we’ll be exploring the wider role of viruses in the Earth’s ecosystem and the evolution of life.

#1. Life as we know it couldn’t exist without them

Emerman M, Malik HS

Viruses have been around for as long as life itself. They may even be the origins of life.

Most of us think of viruses as being exclusively bad things that make us sick. Indeed, many of them do, which is why we also know them as pathogens. At the same time, evolution couldn’t exist without them. In fact, viruses are incredibly ancient, and while most don’t leave behind fossils due to their tiny nanometre-scale size, the evidence of their role in evolution is abundant. They may even be the origins of life itself. After all, they’re very simple organic structures compared to living organisms, and may have contributed to the rise of bacteria and archaea which, billions of years later, gave rise to plants and animals.

#2. We can strategically eradicate harmful viruses

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Vaccines and globally-coordinated eradication programmes can help us fight harmful viruses.

As the coronavirus sweeps across the world, it’s important to maintain hope in the wonders of modern medicine, which has allowed us to regain control over the future of our species. In 1798, English physician Edwin Jenner, created the first vaccination in an effort to fight the scourge of smallpox. In 1980, after globally coordinated efforts spearheaded by organisations like the WHO, the variola virus which caused it, was declared eradicated. Numerous other harmful viruses no longer pose a threat thanks to vaccinations and antiviral drugs, similarly to how other vaccinations and antibiotics have eradicated many bacterial diseases.

#3. Viruses affect all the domains of life on Earth

Annina Breen

Viruses can infect every living organism from the tiniest microbes to plants and animals.

We tend to think of viruses as a problem affecting humans and animals, but they’re also found in all other forms of life. The first pathogen to be definitively determined to be viral in nature was in fact the tobacco mosaic virus which, as the name suggests, targets the tobacco plant (along with many other species of nightshade). Eukaryotes, such as plants, animals, and fungi, aren’t the only ones affected by viral pathogens. Other viruses target microorganisms. For example, in just one millilitre of seawater, there are around a billion bacteriophages, which play a vital role in regulating bacterial evolution.

#4. Certain viruses help make us healthier

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Some viruses, such as bacteriophages, can fight harmful infections and boost our immune systems.

Most of us know that, to become immune to a certain ailment, sometimes you have to contract it first, which is the basis of how vaccines work. But some viral proteins help us build up our immune systems before we’re even born. Others destroy harmful bacteria in the digestive, respiratory, and reproductive systems. By their very nature, all viruses are infectious, but that’s not always a bad thing. In another example, herpes viruses, when they’re latent, can help natural killer cells identify cancerous cells infected by other pathogens resulting in an immune system response. In fact, garnering a better understanding of the therapeutic nature of some viruses is an active area of study in modern medicine.

#5. Are viruses a form of life?

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Viruses do not belong to any of the three domains of life, but they do share some things in common with living organisms.

One of the most common questions about viruses is whether they’re alive or not. The general consensus among biologists is that they’re not, because they don’t meet the seven characteristics of life. Most importantly, they have no cellular structure, and neither can they reproduce on their own. They can only replicate and mutate when infecting a host cell. However, the definition of life itself carries some flexibility, since certain species of bacteria can’t reproduce outside of a host cell either. As such, viruses are sometimes considered to be ‘organisms on the edge of life’. The truth is, that no one really knows for sure.

#6. Dormant viruses may lie dormant under the ice

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Many dormant viruses and bacteria may lie beneath the glaciers and ice sheets of the Arctic

When it comes to climate change, the first things that usually come to mind are rising sea levels, deforestation, and pollution. Yet there’s a lesser known and perhaps even more deadly threat if we don’t start getting our impact on the environment in check. It lives under the permafrost in places like Greenland, which are under constant threat of melting. This could result in releasing ancient viruses which have been dormant beneath the ice sheets for thousands or even millions of years. Viruses, along with some strains of bacteria, will be reanimated after being preserved in frigid conditions, unleashing a Pandora’s box of pathogens.

#7. Retroviruses are often used in gene therapy

Mrdavis21

Illustration of the life cycle of a retrovirus (see description for more)

Although still an experimental area of medicine, gene therapy is a technique which involves inserting modified genes into a patient’s cells to treat or prevent diseases. It’s especially promising in the treatment of hereditary conditions, various cancers, and certain viral infections. It’s currently being tested on diseases that have no other cures. It works by deliberately infecting cells with viruses containing genetic material that compensates for missing or abnormal genes. This helps restore the functions of specific proteins. Viruses are crucial, since they’re the delivery method for replacing or adding the necessary genes.

#8. Viruses play a vital role in genetic diversity

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Viruses are primary delivery vectors for genetic material between species

Life and evolution could not exist without the movement of genetic material between species. While reproduction transfers genetic information within the same species, horizontal gene transfer transfers it between different organisms across all domains of life. For example, pollinating insects like bees enabled the rise of flowering plants during the Cretaceous Period. Similarly, viruses have played a central role in forming new species of eukaryotic organisms by spreading genetic material. It’s now widely believed that viruses were especially important in early evolution before the last universal common ancestor diversified into the three domains of life we know today.

#9. Most of the viruses embedded in our DNA are long extinct

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Most of the viral genetic code making up the human genome has been extinct for millions of years.

Viruses exist everywhere to the extent they’re an inseparable part of the planet’s biosphere. The total number of viruses in the ocean, for example, may be as high as 10³¹ – that’s 10 followed by 31 zeros. In fact, around 8% of the human genome is composed from viruses which infected our ancestors long ago. That’s about four times higher than the amount of genetic material provided by our genes. Even more amazingly, most of this DNA belongs to viruses which have been extinct for millions of years. Consider, for example, the fact that viral infections in ancient sea life played an integral role in the migration of life from the oceans to the land.

#10. Viral evolution helps us better understand human prehistory

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A map of human migration patterns over the past 200,000 years

Viruses can also help us trace ancient human and animal migration patterns. For example, the HLTV-2 virus, thought to have originated in Africa and, ultimately, from old-world monkeys, has been found among indigenous peoples in the Brazilian Amazon region. The wider distribution of the virus across the Americas and Eurasia indicates that humans first crossed the Bering Strait up to 13,000 years ago. Because the native Amazonian populations are among the most secluded in the world, they’re among the most reliable markers for ancient migrations to South America. Similarly, the evolution of the JC virus, which is as old as humans themselves, indicates two distinct migrations from Africa starting around 50,000 years ago.

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Viruses are undeniably the most successful inhabitants of Earth’s biosphere. On one hand, this makes infectious viral diseases among the greatest threat to humanity but, on the other, biodiversity and evolution cannot live without them. Fortunately, human intellect and modern medicine have endowed us with the opportunity to change the course of our own evolution. Whether we use this knowledge for good or for bad isn’t up to nature – it’s up to us.

Further Reading