"99% of viruses are beneficial"

“99% of viruses are beneficial”, Philip Yancey just said, in the podcast I’m listening to (“Unbelievable”).

Could someone elaborate on this?

One of my great regrets is avoiding biology at school and university!

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Beneficial for what? From the viewpoint of animals and plants facing extinction a virus that wipes out 99% of humans would be highly beneficial. Most viruses are probably beneficial for themselves; they reproduce so the variety continues to exist. Most are probably neutral to humans (probably far more than 99%) because they don’t infect humans though since we humans have a direct interest in the viruses that do infect us we probably know more of them. Another percentage infect animals or plants we depend upon. I can imagine a very small percentage (perhaps 1%?) of the known viruses negatively affect humans directly or indirectly. That does not mean that the other 99% are beneficial; it could just mean most are neutral. A few viruses may be beneficial because they attack things that attack us.

The following may be of interest
Pride, David. 2020, “Viruses Can Help Us as Well as Harm Us.” Scientific American. Accessed March 18, 2022. https://www.scientificamerican.com/article/viruses-can-help-us-as-well-as-harm-us/

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Good article! Thanks. I enjoyed it

I often wish people kept bibliographies of factoids like that. Maybe it’s true, butI so wish Yancey had given a source the rest of us could follow upon.

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I was surprised to hear that viruses might play a useful role to ourselves or life in general. I assumed it was mistaken and the art it was bacteria that fit that description. I’m still doubtful about viruses but will take a look at the article.

The coolest part of it is gene therapy and research into DNA, as you can use viruses as vectors to insert DNA into other genomes, which the cells then use to make proteins, etc… You can also find tobacco plants with firefly genes with viral insertions that glow in certain conditions


And endogenous human retroviruses compose about 1% of the human genome


Good article! Thanks. I think I remember (way back in the '90s) when my genetics prof said HERVs caused an increased susceptibility to cold sores (HSV1), which is certainly prevalent in my family, for example. This article really helps explain some even more fascinating aspects of evolution and genetic makeup

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I recall from somewhere that they play a role in keeping our microbiome balanced out. The enemy of my enemy is my friend. That does not, of course, make them purposeful anymore than their targeted pathological microbes would be purposeful.


In a larger sense, viruses are vital components of balanced ecosystems. This reference is outdated, but indicates this is a topic of study.


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Ah we have talked about this before but i don’t remember where. Maybe Praveen’s pod? or the Coronavirus pod with him in it?

let me see if i can find them

Praveen: You know, we tend to talk about the viruses when a pandemic like this hits us or when the flu is particularly bad one season and the vaccine isn’t working well. Those are the times that we tend to talk about viruses in the lay community. And that’s understandable because, hopefully, we don’t have to interact too often with viruses that are pathogenic to us. But the reality is, as you alluded to in the beginning, Jim, there are 10 to the 31, or at least that’s one estimate out there, of viruses. And again, as you said, 10 million times more than the number of you know, estimated stars in the universe. This is an unfathomable number, and I think should immediately lead us to ask, why? Why in the world do we have 10 to the 31 viruses? I mean, what does that mean?

And, pretty quickly, when you start studying this, you realize that the vast majority of the viruses out there, vast, vast, vast majority, are not infecting humans or even other animals, but they’re infecting bacteria. And bacteria are also extraordinarily prevalent in the world, more so than we tend to appreciate, right? On the same order of magnitude as viruses and bacteria are absolutely critical for life as we know it. They are, as we say, primary producers, right? They take in-organic material and kind of help make organic material so that life as we know it can exist and humanity can exist in the way that we do. But bacteria are such prolific multipliers. If there was no check on bacteria, they would overtake the world. We wouldn’t exist. And, so, the vast majority of viruses actually seem to be present in order to keep the bacteria in check.


Thanks! That is quite a microscopic ecology. I’ll have to review this one!

I don’t buy that. I would be absolutely stunned if bacteriophages played any significant role in limiting bacterial populations. To my knowledge, the primary limitation for bacterial populations is limited resources.

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What kills or limits bacteria.

  • limited resources
  • unsuitable environment (e.g., too much heat, adverse chemicals)
  • bacteriophage (viruses that infect bacteria)
  • predatory bacteria (some bacteria eat bacteria)
  • some protozoans
  • some larger animals that specialize in eating bacteria such as c. elegans
  • probably some others

Mu, Da-Shuai, Shuo Wang, Qi-Yun Liang, Zhao-Zhong Du, Renmao Tian, Yang Ouyang, Xin-Peng Wang, et al. 2020. “Bradymonabacteria, a Novel Bacterial Predator Group with Versatile Survival Strategies in Saline Environments.” Microbiome 8 (1): 126. Bradymonabacteria, a novel bacterial predator group with versatile survival strategies in saline environments | Microbiome | Full Text.

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I would put autolysis just after limited resources, especially for spore formers. Autolysis is somewhat analogous to apoptosis/autophagy in complex eukaryotes. One of the spore forming bacteria I have worked with has >90% die off of vegetative organisms just hours after reaching maximum density, and this is all a result of genetics.


I recall that most of the marine viruses are bacteriophages of some sort or another. Another challenge in interpreting such factoids is whether that’s 99% of individuals or of kinds.

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I went off Yancy, and Unbelievable years ago.

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