They're not alive, but they're more alive than dead*
A few days ago a dear friend told me that after reading the entry “What is life?”, from this blog, he wondered if, based on the characteristics of the living beings discussed in that entry, viruses would be alive. I haven't stopped thinking about it for days.
So in today's run I started thinking about how viruses fit into each of the characteristics that I used to define living beings, let's see.
1. It is self-contained. It has a structure that separates it from its surroundings and environment.
Well…YES, viruses have a structure that separates them from their environment, but unlike the cell membrane of living beings, which is mainly composed of phospholipids, of viruses is primarily made of proteins. Furthermore, inside these, there are only ribonucleic acids, unlike living beings that have several organelles.
2. It has an exchange of materials and energy between its internal structure and what is outside (metabolism) in such a way that its internal structure remains as variable as possible (homeostasis).
Well, this feature has two parts, let's look at the first. Do viruses exchange materials or energy between their internal and external environment? NO, they have no metabolism. Second, do they have homeostasis? NO, their internal structure does not have any type of variations, they are completely inert.
3. It is capable of obtaining or generating the energy necessary to maintain homeostasis.
NO, as long as they do not interact with any living being, they are, I repeat, completely inert, they do not use or generate any type of energy or anything.
4. It can self-replicate almost perfectly, almost.
Definitely, NO, viruses are not AUTO-replicate, they require living beings, which they parasitize, to reproduce. But to make their copies they use nucleic acids, which is the material that living beings use to store their genetic information. Viral nucleic acids “hack” the system of living beings so that copies of the viruses are made. These copies are almost perfect.
5. That small imperfection in making copies of itself allows variants to exist sufficiently for there to be natural selection.
Are the variants of the copies of the viruses enough for there to be natural selection? YES, in viruses there is natural selection, therefore they evolve.
So, to be strict, viruses only meet two of the five characteristics, so they cannot be considered living beings. But, without a doubt, they are closely related to living beings.
The fact that they use nucleic acids for their reproduction tells us that their relationship with living beings is very close. All living beings use them for their functioning, not just reproduction, since these compounds are where all the genetic information of the cells, the genes, is stored. With this information, proteins are formed, not only the structural ones but also the operational ones, those that fulfill, or regulate, the functions related to characteristics two and three of the commented list.
The fact that living beings and viruses are so related can be explained in two ways:
First, among the first proto-organisms, which began to appear at the beginning of life, were viruses. Specializing, later, in parasitizing those that finally gave rise to living beings. It sounds interesting, but the fact that they have a protein coating makes me doubt that this is the case, the only known source of proteins, not amino acids, are living beings.
Second, they have originally been living beings and have subsequently over-specialized in leading a parasitic life. Their only function is to leave a copy of their genes, which they do very successfully. This is very much in line with Richard Dawkins' “selfish gene” theory.
That also has to do with what was said about viruses and category four on the list. Viruses use their nucleic acids to take over the machinery of the living being they parasitize, turning it into a machine for making copies of the virus. There are several interesting things here, two in particular.
The first is, is there a probability that genetic material from viruses will be integrated into the genome of their hosts? If this is possible, does it affect the evolution of the hosts?
If virus genes can integrate into host genes, this is called horizontal gene transfer (HGT) and, yes, it has implications for evolution. For example, we know that about 30% of the protein divergence that has occurred in us humans since we diverged from bonobos and chimpanzees is due to HGT. But this transfer can also help hosts generate more effective immune responses. Do you want to be more surprised? According to some studies, HGT with viruses may have affected the development of the placenta in placental mammals.
But this happens in both directions, genes from the hosts can pass to the Viruses. There are examples where this is seen to allow viruses to become more effective in the process of hijacking the host's cellular machinery.
So living beings and viruses co-evolve, affecting each other.
Second, how fast do viruses evolve? Well, that varies a lot, some evolve very quickly and others that evolve more slowly. In general, we can divide viruses into two groups, depending on the type of nucleic acid they use. RNA viruses and DNA viruses. The former evolve faster for three reasons. First, its replication is more prone to errors, mutations. Second, they do not have error correction mechanisms. Third, their reproduction is faster, generating more mutants faster. That is why the most difficult viral diseases to eradicate, such as AIDS, influenza, and colds (caused by coronaviruses) are RNA viruses.
In conclusion, I do not fail to get the flu vaccine every year since they're not alive, but they're more alive than dead. *Originally posted as: "But I don't miss getting the flu shot"
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