why aren’t viruses “alive”?

Question

Hi everyone,

I’m not very knowledgeable about science, so I’m struggling to understand the notion that viruses aren’t “alive”, and the robot analogies people use. I understand that they don’t have some of the characteristics (cells, ability to reproduce), but my mind can’t wrap itself around the notion that they’re like objects. Can you please give some examples that could explain this in a way that is accessible to someone who isn’t very advanced in the subject?

Thanks

EDIT: wow thanks so much guys for so many amazing replies!!!

In: 29

Answer 1

The question is embarrassing for biologists, because it really is a matter of definition.

A very thorough definition of “being alive” (at least on Earth) would be composed of the following (simplified) points:

– being a cell, or being composed of cells
– being able to “use” outside source of energy to grow and maintain yourself
– being able to reproduce in way that your “species” will subjected to Darwinian evolution

Now, viruses do not check the two first points. However, the first point is often considered to be an arbitrary addition to the definition that just happens to be true to everything consensually called “alive” on Earth.

The second point really is the crux of the issue for viruses: by themselves, they are not able to “use energy” (they do not have a metabolism), and many people consider this to be a fundamental point of “being alive”.

But saying that they do not belong to the realm of life isn’t really true either, because not only do they check the third point, they also very often and strongly interact, at the genetic and evolutionary level, with entities we consensually call “alive” (bacteria, animals, plants, etc…).

So, they are a kind of middle-point in the definition of live, and depending on what you choose to include in “life”, you might include them or not. Fully including or excluding them is very difficult, hence the embarrassement for biologists…

Personally, I consider this question to be rather moot, once you’ve realised which part of the definition above they check or not. Then it “just” (it’s a bit more complicated really) becomes a matter of arbitrary threshold.