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Are viruses living, once living, or never living?
Question Date: 2014-07-30
Answer 1:

Our definition of the word "living" doesn't really account for viruses. They tend to blur the lines.

Viruses don't contain within themselves all of the information they need to replicate, unlike living cells, which do. For this reason, we do not consider viruses to be organisms in the sense that you and I are.

However, viruses can reproduce with help, and their ability to reproduce and the information that distinguishes one virus from another behaves in a very life-like way. Viruses can evolve by natural selection, for example; this is why disease-causing viruses eventually become resistant to the drugs we use to fight them.

In reality, nature does not make such neat and tidy distinctions between living and nonliving that we like to identify, and viruses are an example of something that makes our human-made distinctions somewhat blurry. There are other examples that I can think of, too: the cells in a tree that make up its wood are not living cells, but the tree itself certainly is alive, and without the wood it would die, because it couldn't get water up from the ground into the leaves where it gets used. So is wood living or is it dead? I could ask the same question about the crystals of mineral that make up your bones and teeth, and so on.

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