Viruses may be nonliving, but they're about as close to living as you can get without crossing the line.
I'd suggest "The selfish gene" as an interesting read to help put the concept of replicative genes in perspective.
Simply put, stable things survive. You can be stable in a durability, or stable in a temporal sense, you replicate and make more of yourself.
Prions would be a good example of this phenomenon.
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