Viruses selected by evolution?

Question

First let me apologize in advance for I know almost nothing about biology. I had a conversation today with a family member who is a bio-computer-scientist and he talked to me about what his colleagues (biologist) are doing and I feel a bit confused about what he explained (for my defense I feel he was a bit confused too). For background : they work in Chile and are studying plants that live in the desert (Atacama). If I understand correctly his team is trying to explore the idea (is it a new idea ?) that some viruses might actually be good for the plants they are infecting and might have been "selected" and are now "part" of the species. The way I understand it is that they collect samples of plants and somehow by analyzing their DNA notice that these plants are all infected by some kind of virus and they tell themselves that maybe if all the plants have the virus it's because it's good for the plants. I guess my questions would be : 1) Does any of this make sense ? 2) If it does how would the selection process happen ? Combining my (old) high-school knowledge and wikipedia I see a virus as a piece of DNA that goes into a cell and then uses the cell's tools for it's own purpose, but it is not part of DNA. So how can it be treated as part of the plant ? 3) Do you know any good references (preferably for an enthusiast layman) about this subject (i.e. the potential good of some viruses and maybe potential applications in bio-engineering) ? I find especially fascinating the idea that maybe evolution isn't just the result of mutations but also of "contamination".

Answer 1

This makes complete sense! Your family member is talking about a fascinating and rapidly growing field of biology called viral mutualism or symbiosis.

Here are the answers step-by-step to your questions :

1. Does any of this make sense?

Yes, absolutely. While we usually think of viruses as bad guys that cause disease, many viruses actually form beneficial (mutualistic) relationships with their hosts.

In harsh environments like the Atacama Desert, survival is incredibly difficult. If scientists are finding that every single plant of a certain species carries a specific virus, it is highly likely that the virus is giving the plant a superpower—such as drought tolerance, heat resistance, or a better ability to absorb scarce nutrients. Plants without the virus simply die off, leaving only the "infected" (and thus protected) plants to reproduce.

2. How does the selection process happen?

You have a great memory from high school! You are right that a typical virus enters a cell, uses its machinery, and floats around as a separate entity. However, there are two main ways a virus becomes a permanent "part" of a species through evolution:

1. 1 Vertical Transmission: Some viruses don't kill the host cell; they just live inside it quietly. When the plant produces seeds, the virus is packed right along inside the seed. The offspring are born with the virus already inside them. Because it's passed down from parent to child generation after generation, it effectively acts like a permanent part of the plant's biology.
2. 2 Genetic Integration (Endogenous Viruses): Sometimes, a virus literally stitches its own genetic code directly into the plant's DNA. If this happens in the plant's reproductive cells (like pollen or ovules), that viral DNA becomes a permanent gene in the plant’s genome. Over millions of years, this happens so often that a massive chunk of the DNA of modern plants and animals (including humans!) is actually made of ancient, tamed viruses.

So, evolution isn't just about a single organism mutating; it's also about symbiogenesis—two entirely different organisms fusing together to create something new.

3. Good References for an Enthusiast Layman

If you want to dive deeper into this mind-bending concept, here are some great, accessible starting points:

1. Books:
2. Virolution by Frank Ryan. This is the ultimate layman's book on this exact topic. It explains how viruses are a driving force in evolution and how we wouldn't even be human without them.
3. A Planet of Viruses by Carl Zimmer. A very short, beautifully written, and easy-to-read book that changes how you view viruses.
4. Famous Real-World Examples to Google:
5. The Yellowstone Panic Grass: Look up the Dicanthelium lanuginosum grass in Yellowstone. It can only survive in scalding geothermal soils if it is infected by a fungus, which itself must be infected by a specific virus. If you cure the fungus of the virus, the plant dies from the heat!
6. The Mammalian Placenta: If you want a human example, look up Syncytin-1. Humans can only grow a placenta during pregnancy because of an ancient viral gene we "stole" millions of years ago. Without that virus, humans couldn't give birth to live young.