We exist because of Viruses — Almost half of the Human Genome is derived from Viruses.

Humans evolving from Apes made Charles Darwin the joke of the 19th century, but how about Humans existing because of Viruses.

Photo by National Cancer Institute on Unsplash

In one of my articles, I talked about the ‘gene’ as the indivisible component of being, meaning all organisms act like vehicles or careers of different genes. This makes the gene an immortal component of life because it is always calculating how to pass its copies to the next generation, especially when the current vehicle (organism) is reaching senescence.

In this article, I’ll delve into one of the mechanisms where the gene finds a way to survive by applying for permanent residence in the host organism it was supposed to bio-terrorize resulting in symbiosis. Symbiosis, in this case, is a kind of agreement where the invading gene is integrated into the organism’s genome, and in return, it performs a function in the organism or at least repents from killing its host. So it’s more of a win-win; no one dies.

The non-human living within us.

Only 1% of the Human genome has been known to code for all the proteins in the human body. However, about 40% of our genome contains repetitive sequences, and 8% contains retroviral relics. These repetitive and retroviral-derived sequences have viral origins.

What could be the reason why the human body burdens itself with such an immense genomic size when it is considerably an energy-consuming process to replicate and maintain such a genome?

1. Non-coding sites could act as sacrificial lambs that protect the coding sites. Mutations on the protein-coding sites can cause non-functional proteins, which might result in disadvantageous phenotypes, so the genome has to keep these sites intact like they mean it. DNA can react with very reactive molecules (mutagens) like radicals or reactive oxygen species. This disrupts the structure of nucleotides making up the nucleic acid (DNA), resulting in errors when replicating or transcribing these genes. So my thinking is that instead of having a genome made up of just 1% of coding genes exposed to mutagens, it is better to have the +99% of non-coding genes that can react with most of the mutagens. It is a game of numbers here, the attack of an essential gene is like hitting a needle in a haystack.
2. With reference to studies in non-human organisms like mice and chickens, it has been shown that when the host organism integrates viral elements into its genome, it garners immunity against ‘like’ viruses. Perhaps these viral elements can be used by the host cells to learn about the virus's strengths and weaknesses. Take it as humans capturing an alien to study it to learn their weaknesses (‘Independence Day’ movies come in handy here).
3. Another interesting phenomenon is ‘gene birth’. This used to be an ongoing debate in evolutionary biology and related fields, whether genes are born ‘de novo’ or from a change in function of other genes. When studying evolutionary dynamics of genes, some genes seem to undergo faster evolutionary rates than other genes. In conclusion with support from other studies, it was observed that some genes are born from the start (de novo). These new genes are the ones that undergo faster evolutionary rates than older genes because they are still moulding themselves to produce best-fit proteins for the newly-found function. This birth of genes comes from the vast reservoir of non-coding sites, which includes approximately half of the genome originating from viral elements. Nature is clever, huh. A well-studied example of de novo gene birth is the anti-freeze glycoproteins found in codfish.
4. Specifically, Endogenous Retroviruses have been found to produce functional proteins, which prove to be very important in the pregnancy of humans and other mammals. These ERV-derived genes play special roles in the placenta where they mediate foeto-maternal tolerance (minimising rejection of the foetal tissue by the mother’s tissue ), and some are responsible for attachment of placental cell lines. Without these proteins, humans and other animals, which require the placenta for gestation, would not exist. Or would Nature find another way? I do not know. I saved this for last because it fits the title of my article best.

As much as I want to go deeper about ERVs, I think I would end up defeating the focus of this article, so it's best saved for my next article. However, Viruses are not always enemies as such it's just a matter of natural selection, if you take it as genes trying to survive, we would note that whether I am a virus or bacteria or human being, we are serving our Gene masters’ purpose.

So no reason to take life too seriously, we are here to make copies of our masters’ signatures and pass them to the next generation. If you choose not to propagate, perhaps your siblings with the same set of genes will pass it for you. That is why we are always protective of people with similar genes to us (relatives) because they have all or some of our Master’s signatures in need of protection. Nature is wily 😈.