Is the coronavirus a living thing?

The question of whether viruses are living things has generated huge interest following the global impact of covid-19. An evolutionary perspective may provide the answer.

In textbooks, viruses are inert creatures. They do not meet the criteria that define a living being. Coronavirus among them is not a cellular organism, with metabolism, growth and development, homeostasis, response to stimuli and the environment. In the definition, it meets only two main characteristics: it develops and reproduces, although, since it does not have its own ribosomes, it requires the mechanism of a host cell, such as a person, to reproduce.

With such signs, viruses, especially coronavirus, are they not living beings?

Despite what the textbooks say, there is no scientific consensus when it comes to including them in the tree of life. A recent publication by researchers Hugh Harris and Colin Hillen in frontiers of microbiology makes it obvious.

They are extremely simple.

Since the description of the first tobacco virus by scientist Dmitry Ivanovsky in 1892, more than 9,000 types of viruses have been described in detail, although it is estimated that there are millions of types in the environment. And they are all extremely simple. They consist of genetic material (RNA or DNA), a protein capsid, and, in some cases, a lipid envelope.

Unlike cells, viruses do not have all genes common to them, so it is not possible to find out their global phylogenetic tree, that is, the relationships between them and their common ancestor, at least exclusively on the basis of genetic material.

Although there is no consensus in the scientific community about the living or inert nature of viruses, there is a consensus that they are polyphyletic, that is, they have multiple evolutionary origins, and this suggests the additional problem of discovering this global phylogeny, as well as giving them a place on the tree of life. .

When did they appear on Earth? Where are they from?

Viruses could have appeared even before cells; they may be the result of reduction or degeneration of cells that have simplified adaptation to parasitism.

If so, they would be after the first cellular organism and before LUCA, the most recent common ancestor of cellular organisms, that is, the most recent common ancestor of the three domains that exist today: bacteria, archaea, and eukaryotes.

There is also the escape or wandering hypothesis, which postulates the origin of viruses as a consequence of the evolution of genes that have disrupted their role inside cells in order to lead a parasitic existence on their own.

Whatever its origin, it is closely related to the evolution of life on Earth, and in particular to the evolution of cellular life. None of the three hypotheses alone can fully explain its appearance.

Philosophical question: to be or not to be

In fact, the inclusion or non-inclusion of viruses in the number of living organisms is a question, at least in part, philosophical, since it depends on the definition of a living being that we want to consider.

For NASA, life is a self-sustaining chemical system capable of Darwinian evolution. This definition, including self-sufficiency, excludes viruses because they are not capable of replicating on their own, they need a host technique.

Evolutionary biologist Richard Dawkins defined life as the non-random outcome of survival through the reproduction of random variables. This definition by Dawkins explicitly includes viruses among living beings.

Patrick Forter, a researcher at the Pasteur Institute in Paris (France), is an outspoken advocate for the wildlife of viruses. He proposed to define a living organism as a set of integrated organs (molecular or cellular) that produce individuals that evolve as a result of natural selection.

Evolutionary point of view gives them life

From an evolutionary and ecological point of view, viruses are living beings, or at least mimic them very well.

Viruses, as we see in the example of the coronavirus, are subject to evolution and natural selection in the same way as any other living being. Viruses (hosts) and cells (hosts) co-evolve as a result of their antagonistic relationship.

Various viruses can be grouped into species or types of viruses (or at least individual evolutionary units), which are further subject to taxonomic and systematic classification into higher categories (genus, family, etc.). And they all contain genetic material with which we can derive phylogenies, or trees of life. Like all living things, viruses store their genetic information in these nucleic acids and share the same (or very similar) genetic code.

They reproduce, although not on their own, as is the case with other parasitic organisms such as endoparasitic bacteria.

Percentage of human genetic material is of viral origin.

Viruses developed and evolved along with cellular life, participating in regular horizontal transfers of genetic material with their cellular hosts, probably playing a key role in cellular evolution.

Without going too far, it has been estimated that a very significant percentage of human genetic material is of viral origin.

If the origin (or origin) of viruses is inseparable from the evolution of cellular life, then how can we exclude them from the tree of life?

All this leads to the conclusion that the coronavirus, at least from an evolutionary point of view, is as alive as we are.

Martial Escudero, Professor of the Department of Plant Biology and Ecology, Seville University

This article was originally published on The Conversation. Read the original.