The question of whether viruses are living beings has gained immense interest following the global impact of COVID-19. An evolutionary perspective may provide the answer.
In textbooks, viruses are inactive creatures. They do not meet the criteria that define a living being. Corona virus among them, is not a unicellular organism, which has metabolism, growth and development, homeostasis, response to stimuli and environment. It fulfills only two basic characteristics by definition: it grows and reproduces, however, since it does not contain ribosomes of its own, it requires the machinery of the cell host to reproduce, for example a Human.
With these signs, viruses, especially the coronavirus, aren’t they 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 Hylan Frontiers in Microbiology clarifies.
they are very simple
Since the first tobacco virus was described by scientist Dmitri Ivanovsky in 1892, more than 9,000 virus species have been described in detail, although it is estimated that there are millions of types in the environment. And they are all very simple. They are composed of genetic material (RNA or DNA), a protein capsid and in some cases a lipid coat.
Unlike cells, viruses do not have genes common to all of them, so it is not possible to trace their global phylogenetic tree, that is, the family relationships between them and their common lineage, at least based exclusively on genetic material. Huh.
Although there is no consensus in the scientific community on the living or dormant nature of viruses, there is a consensus to say that they are polyphyletic, that is, they have multiple evolutionary origins, and this presupposes an additional problem of finding this global phylogeny. as well as to place them on the tree of life.
When did they appear on earth? where do they come from?
Viruses could have appeared even before cells; They may be the result of depletion or degeneration of cells, which have become simpler to adapt to parasitism.
If so, they would be after the first unicellular organism and before LUCA, the most recent common ancestor of unicellular 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 result of the evolution of genes that automatically adopted a parasitic existence by breaking their role inside cells.
Whatever its origin, it is closely related to the development of life on Earth, and in particular to the development of cellular life. None of the three hypotheses alone can fully explain its appearance.
A Philosophical Question: To Be or Not to Be
Indeed, whether or not viruses are included among living organisms is a question, at least partly, philosophical, as it depends on the definition of living organism we wish to consider.
For NASA, life is a self-sustaining chemical system capable of Darwinian evolution. This definition excludes viruses, including self-sufficiency, because they are not capable of replicating on their own, requiring the host’s machinery.
Evolutionary biologist Richard Dawkins defined life as the non-random survival result of replication of random variables. This definition of Dawkins would obviously include viruses among living things.
Patrick Fortere, a researcher at the Pasteur Institute in Paris (France), is an ardent defender of the living nature of the virus. He proposed to define a living organism as a set of integrated organs (molecular or cellular) that produce individuals that evolve through natural selection.
evolutionary perspective gives them life
From an evolutionary and ecological perspective, viruses are living beings, or at least they mimic them very well.
Viruses, as we see with the coronavirus, are subject to evolution and natural selection, remarkably similar to any other living thing. Viruses (hosts) and cells (hosts) unite as a result of their antagonistic relationship.
Different viruses can be classified into virus species or types (or at least discrete evolutionary units) which are further classified into higher categories (genus, family, etc.) and subject to systematic classification. And they all contain genetic material with which we can infer the phylogeny or tree of life. Like the rest of living organisms, viruses store their genetic information in these nucleic acids and share the same (or very similar) genetic code.
They reproduce, though not by themselves, as is the case with other parasitic organisms such as endoparasitic bacteria.
One percent of human genetic material is of viral origin
Viruses have evolved and co-evolved with cellular life by participating in regular horizontal transfer events of genetic material with their cellular hosts, possibly playing an important role in cellular evolution.
Without going too far, it is 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, how do we exclude them from the tree of life?
All this leads to the conclusion that the coronavirus is as alive as you and I, at least from an evolutionary perspective.